Science

101 Best Science Experiments You Can Do at Home

101 safe science experiments with household items, covering kitchen chemistry, crystals, plants, microbes, the human body, Earth, weather and the night sky.

By BlogAI Editors · · 52 min read

A kitchen is a surprisingly good laboratory. Red cabbage makes a pH indicator, a strawberry gives up its DNA to dish soap and rubbing alcohol, and a packet of yeast blows up a balloon. This list gives you 101 science experiments you can do at home with everyday materials, grouped by subject. Each one lists what you need, what to do, and why it works.

The list concentrates on chemistry, biology, Earth science, weather and astronomy. If you are after forces, sound, light, electricity and magnetism, we cover those separately in 101 physics experiments you can do at home, so they are not repeated here.

About this list. These are well-known classroom and science-centre activities adapted for home materials. The explanations follow the OpenStax chemistry and biology textbooks and activity collections from the American Chemical Society, the Exploratorium and Science Buddies (see References). We did not run each one for this article. Results depend on your materials, temperature and timing, so if something does not work the first time, change one thing and try again.

Safety first

Read these rules before you start, and make sure children do too:

  • An adult should be present for anything marked Adult. That includes every experiment with heat, boiling water, flames, rubbing alcohol, iodine, borax or sharp tools.
  • Wear eye protection (safety glasses or swimming goggles) for anything that fizzes, foams or splashes.
  • Never mix cleaning products. Bleach mixed with vinegar or other acids releases chlorine gas, and bleach mixed with ammonia releases toxic chloramine vapours. None of the experiments below uses bleach.
  • Do not taste anything unless the experiment says it is food and is prepared with clean kitchen equipment. Do not eat experiments afterwards.
  • Label every container and keep chemicals away from young children and pets.
  • Keep mould and microbe experiments sealed. Never open a bag or jar of mould; throw it away unopened. Anyone with allergies or asthma should skip those experiments.
  • Rubbing alcohol is flammable. Keep it away from flames and heat, and use it in a ventilated room.
  • Wash your hands after every experiment.

How to turn an activity into an experiment

Watching something happen is a demonstration. It becomes an experiment when you ask a question, change one thing on purpose and measure the result:

  1. Ask a question you can test, such as "Does warm water make yeast produce gas faster?"
  2. Predict what will happen and write down why.
  3. Change one variable (temperature, amount, time, type of liquid) and keep everything else the same.
  4. Include a control, an identical setup where you do not make the change, so you can compare.
  5. Measure and repeat. Use a ruler, thermometer, kitchen scale or timer, and do each trial at least three times.
  6. Record everything, including results that surprise you.

When you are ready for a longer investigation, our list of 101 science projects for students builds many of these activities into full projects.

Acids, bases and indicators

Acids and bases are everywhere in a kitchen. Indicators change colour to show which is which (OpenStax Chemistry 2e, chapter 14).

1. Red cabbage pH indicator

You need: Half a red cabbage, a knife, hot water from a kettle, a jug, a sieve. Adult for chopping and hot water.

Do it: Chop the cabbage, cover it with hot water and leave it for 20 minutes. Strain off the purple liquid and let it cool. This is your indicator.

Why it works: Red cabbage contains pigments called anthocyanins, which change shape, and therefore colour, depending on how acidic the solution is. They turn red or pink in acids, stay purple near neutral, and turn blue, green and then yellow as the solution becomes more alkaline.

2. A rainbow of household liquids

You need: Red cabbage indicator, clear cups, and liquids to test: lemon juice, vinegar, water, milk, baking soda solution, washing soda solution, soapy water.

Do it: Put a little indicator in each cup and add a different liquid to each. Arrange the cups from red to yellow-green.

Why it works: You have made a rough pH scale. Lemon juice and vinegar turn the indicator red (acidic), baking soda turns it blue-green (mildly alkaline), and washing soda pushes it towards green or yellow (more alkaline). Write down each colour to build your own pH chart.

3. Turmeric indicator paper

You need: Ground turmeric, rubbing alcohol or water, paper towel or coffee filter, baking soda solution, vinegar. Adult if using rubbing alcohol.

Do it: Mix a teaspoon of turmeric with a little rubbing alcohol (or water), paint it onto paper and let it dry. Dab on baking soda solution, then vinegar.

Why it works: Turmeric's yellow pigment, curcumin, turns reddish-brown in alkaline conditions and back to yellow in acid. That is why a curry stain can turn red when you wash it with alkaline soap.

4. Turn an indicator with your breath

You need: Red cabbage indicator diluted with water until it is blue-purple, a tiny pinch of baking soda, a clear glass, a drinking straw.

Do it: Add the baking soda so the indicator turns slightly blue. Then blow gently through the straw into the liquid for a minute or two. Do not suck.

Why it works: The carbon dioxide in your breath dissolves in water to form carbonic acid, which slowly lowers the pH and shifts the colour towards purple or pink. The same chemistry is making the oceans more acidic as they absorb carbon dioxide from the air (NOAA).

5. Chalk, shells and acid

You need: Blackboard chalk (calcium carbonate type) or a seashell, vinegar, a glass, a second glass of water as a control.

Do it: Drop a piece of chalk or shell into vinegar and an identical piece into water. Watch for bubbles and check the pieces each day.

Why it works: Calcium carbonate reacts with acid to produce carbon dioxide gas, water and a dissolved calcium salt, so the chalk slowly disappears. Acid rain erodes limestone and marble statues the same way, and more acidic seawater makes it harder for shellfish and corals to build their shells.

6. Naked egg

You need: A raw egg, a glass, white vinegar.

Do it: Put the egg in the glass, cover it with vinegar and leave it in the fridge for 24 to 48 hours, changing the vinegar once. Gently rinse it.

Why it works: The shell is calcium carbonate, which the vinegar dissolves, releasing bubbles of carbon dioxide. What is left is the egg held together by its thin, flexible membranes. Keep it for the osmosis experiments later in this list, but do not eat it.

7. Rubbery chicken bone

You need: A clean chicken bone from a cooked meal, a jar of vinegar, a lid.

Do it: Leave the bone in vinegar for three to seven days, changing the vinegar every couple of days. Rinse it and try to bend it.

Why it works: Bone gets its hardness from calcium phosphate minerals and its flexibility from the protein collagen. The acid dissolves the minerals and leaves the collagen behind, so the bone bends like rubber. This is why calcium matters for strong bones.

8. Shine dull copper coins

You need: Dull copper or copper-plated coins, vinegar, salt, a bowl, paper towels.

Do it: Mix a quarter cup of vinegar with a teaspoon of salt. Dip half of a coin in for 10 seconds, then rinse it.

Why it works: Copper slowly reacts with oxygen in the air to form a dull layer of copper oxide. The acid and salt together dissolve that layer, revealing shiny copper underneath. Rinse well, or the coin will soon change colour again (see the next experiment).

9. Coins that turn green

You need: Coins cleaned in the previous experiment, left unrinsed, a paper towel.

Do it: Put the vinegar-and-salt coins on a paper towel without rinsing them and check them after an hour and again the next day.

Why it works: With oxygen, acid and salt present, the copper reacts to form green copper compounds. A similar but much slower reaction with air and rain gives copper roofs, and the Statue of Liberty, their green coating, called patina.

10. Copper-plated nail

You need: The salty vinegar used to clean coins (it now contains dissolved copper), a clean steel nail or paperclip, a glass.

Do it: Put the nail into the vinegar solution and leave it for 10 to 30 minutes.

Why it works: Iron is more reactive than copper. Iron atoms on the nail give electrons to the copper ions in the solution, so a thin layer of copper metal forms on the nail while iron dissolves. This is a displacement reaction, and it shows that some metals give up electrons more easily than others.

Chemical reactions and energy

Reactions can release or absorb energy, and they can be fast or slow. These experiments let you see what controls them.

11. A balloon blown up by a reaction

You need: A small plastic bottle, vinegar, baking soda, a balloon, a funnel or spoon.

Do it: Pour a few centimetres of vinegar into the bottle. Use the funnel to put two teaspoons of baking soda inside the balloon. Stretch the balloon over the bottle neck, then lift it so the powder falls in.

Why it works: Baking soda (sodium bicarbonate) reacts with the acetic acid in vinegar to produce carbon dioxide gas, which fills the balloon. Try different amounts of baking soda to see how much gas you can make before the vinegar runs out.

12. Which acid fizzes fastest?

You need: Vinegar, lemon juice, and a solution of citric acid if you have it; baking soda; identical cups; a timer.

Do it: Put the same volume of each acid in separate cups and add the same amount of baking soda to each. Time how long each fizzes and compare the height of the foam.

Why it works: Different acids at different concentrations release hydrogen ions at different rates, so the reaction speed changes. This is a fair test only if you use the same volume of liquid and the same amount of powder each time.

13. Baking soda vs baking powder

You need: Baking soda, baking powder, two cups of plain water, two cups of vinegar.

Do it: Add a spoonful of each powder to water, then to vinegar, and compare.

Why it works: Baking soda only fizzes when you add an acid. Baking powder is baking soda already mixed with a dry acid, so it fizzes in plain water too. That is why recipes with acidic ingredients such as yoghurt or buttermilk often use baking soda, and others use baking powder.

14. A reaction that gets colder

You need: Vinegar, baking soda, a cup, a kitchen or aquarium thermometer.

Do it: Measure the temperature of the vinegar. Stir in two spoonfuls of baking soda and measure again as it fizzes.

Why it works: The temperature drops by a few degrees because this reaction is endothermic: it takes in heat energy from its surroundings. Instant cold packs use a similar idea, dissolving a salt in water in a way that absorbs heat.

15. Steel wool that warms up

You need: A pad of plain steel wool (without soap), vinegar, a jar, a thermometer.

Do it: Soak the steel wool in vinegar for a minute, squeeze it out, wrap it around the bulb of the thermometer and put both in the jar. Watch the temperature over five minutes.

Why it works: The vinegar removes the protective coating on the steel, so the iron starts to rust quickly. Rusting is exothermic, so the temperature rises. Disposable hand warmers use iron powder rusting in a controlled way.

16. Elephant toothpaste

You need: 3 percent hydrogen peroxide (from a pharmacy), a packet of dried yeast, warm water, washing-up liquid, food colouring, a plastic bottle, a tray. Adult; wear eye protection.

Do it: Stand the bottle on the tray. Add half a cup of hydrogen peroxide, a squirt of washing-up liquid and a few drops of colouring. Mix the yeast with three tablespoons of warm water, pour it into the bottle and step back.

Why it works: Yeast contains the enzyme catalase, which rapidly breaks hydrogen peroxide into water and oxygen gas. The soap traps the oxygen in a stream of foam. Feel the bottle afterwards: the reaction gives off heat.

17. Potato catalase

You need: Raw potato, cooked potato, 3 percent hydrogen peroxide, two saucers. Adult.

Do it: Put a slice of raw potato and a slice of cooked potato on separate saucers and add a few drops of hydrogen peroxide to each.

Why it works: The raw potato bubbles because its cells contain catalase, the same enzyme as in yeast. Cooking destroys the enzyme's shape, so the cooked slice barely reacts. Your own cells use catalase to break down hydrogen peroxide, a by-product of normal metabolism.

18. Tablet race: temperature

You need: Effervescent tablets (such as vitamin C or antacid tablets), three glasses, cold, room-temperature and warm water, a timer.

Do it: Fill the glasses with the same amount of water at different temperatures. Drop a tablet in each and time how long each takes to stop fizzing.

Why it works: At higher temperatures, molecules move faster and collide more often and with more energy, so the reaction goes faster. This is one of the most important ideas in chemistry, and it is why we refrigerate food to slow spoilage.

19. Tablet race: surface area

You need: Two effervescent tablets, two glasses of water at the same temperature, a spoon, a timer.

Do it: Crush one tablet into powder and leave the other whole. Drop them into separate glasses at the same moment and time them.

Why it works: The powder reacts much faster because more of its surface is exposed to the water at once. Flour dust and sawdust can be dangerously flammable for the same reason, which is why factories control dust.

20. Pour an invisible gas onto a candle

You need: A tea light, a jug, baking soda, vinegar, a match or lighter. Adult only.

Do it: Light the tea light. In the jug, mix a tablespoon of baking soda with a little vinegar and wait for the fizzing to slow, without letting the foam escape. Gently tip the jug over the candle as if pouring water, without letting any liquid come out.

Why it works: The reaction fills the jug with carbon dioxide, which is denser than air. When you tip the jug, the invisible gas pours down onto the flame and pushes away the oxygen it needs, putting it out. Some fire extinguishers use carbon dioxide.

21. The candle in a jar myth

You need: A tea light, a shallow dish of coloured water, a tall glass jar. Adult only.

Do it: Stand the lit candle in the water and lower the jar over it. Watch the flame go out and the water rise inside the jar.

Why it works: Many books say the water rises because the flame "uses up" oxygen, but burning replaces oxygen with carbon dioxide and water vapour, so that cannot explain much of the rise. Most of it happens after the flame goes out, as the hot gas inside cools and contracts, and water vapour condenses. It is a good lesson in testing popular explanations.

22. What makes iron rust?

You need: Four steel nails, four jars or cups: one with tap water, one with salt water, one with cooking oil, and one empty and dry with a lid.

Do it: Put a nail in each jar and check them every day for a week. Photograph each one.

Why it works: Iron rusts when it reacts with both oxygen and water. The nail in salt water usually rusts fastest, because the dissolved salt helps electric charge move and speeds the reaction. The oil keeps water and air away, and the dry nail barely changes, which is why bridges and cars are painted and oiled.

23. Stop apples going brown

You need: An apple, a knife, plates, lemon juice, salt water, plain water, cling film. Adult for cutting.

Do it: Cut the apple into equal slices. Treat each slice differently (nothing, lemon juice, salt water, plain water, wrapped in cling film) and compare them every 15 minutes.

Why it works: Cutting breaks cells, letting an enzyme called polyphenol oxidase react compounds in the apple with oxygen to form brown pigments. Lemon juice works because its acid slows the enzyme and its vitamin C reacts with oxygen first. Cling film works by keeping oxygen away.

24. Lemon juice invisible ink

You need: Lemon juice, a cotton bud, white paper, a hairdryer or an oven. Adult for heat.

Do it: Write a message in lemon juice and let it dry. Heat the paper with a hairdryer, or have an adult warm it in a low oven, until the writing appears.

Why it works: Heat makes the sugars and acids in the lemon juice break down and darken before the paper does, so the writing turns brown. Never use a candle or a gas flame for this.

25. Grape juice invisible ink

You need: Baking soda, water, a cotton bud, white paper, dark grape juice and a paintbrush.

Do it: Write with a solution of baking soda in water and let it dry. Paint over the paper with grape juice.

Why it works: Dark grape juice contains anthocyanin pigments, like red cabbage. Where the alkaline baking soda is, the pigment changes colour, so your message appears in a different shade from the rest of the page.

Food chemistry

Cooking is a chain of chemical reactions. These experiments use food, but treat them as experiments, not snacks, unless the instructions say otherwise.

26. Make plastic from milk

You need: A cup of milk, four teaspoons of white vinegar, a saucepan or microwave, a sieve, paper towels. Adult for heating.

Do it: Warm the milk until it is hot but not boiling. Stir in the vinegar and watch lumps form. Strain them, press out the liquid with paper towels and mould the curds into a shape. Leave it to dry for two days.

Why it works: Milk contains a protein called casein. Acid makes the casein molecules clump together into a rubbery solid. Before modern plastics, casein plastic was used to make buttons and jewellery.

27. Shake cream into butter

You need: Cold double or whipping cream, a clean jar with a tight lid, a pinch of salt (optional).

Do it: Fill the jar a third full of cream, close it and shake hard. After 5 to 15 minutes the cream thickens, then suddenly separates into a lump of butter and liquid buttermilk.

Why it works: Cream is an emulsion of fat droplets in water, each droplet coated with a thin membrane. Shaking breaks those membranes, letting the fat droplets stick together into butter. Made with clean equipment and cold cream, the butter is safe to eat.

28. Make an emulsion

You need: A jar with a lid, cooking oil, vinegar, a teaspoon of mustard.

Do it: Shake oil and vinegar together and time how long they take to separate. Then add the mustard, shake again and time it.

Why it works: Oil and water do not mix, so they separate quickly. Mustard contains substances that act as emulsifiers, which sit at the boundary between oil and water and keep tiny droplets from joining up. Mayonnaise uses egg yolk, which contains the emulsifier lecithin.

29. Fresh pineapple vs jelly

You need: A packet of gelatin jelly, fresh pineapple, tinned pineapple, small cups. Adult for hot water.

Do it: Make up the jelly. Before it sets, add fresh pineapple to one cup, tinned pineapple to another, and nothing to a third. Put them in the fridge.

Why it works: Fresh pineapple contains bromelain, an enzyme that cuts proteins such as gelatin into pieces, so that jelly does not set. Tinned pineapple has been heated, which destroys the enzyme. That is why jelly packets warn against fresh pineapple and kiwi fruit.

30. Find starch with iodine

You need: Iodine solution (such as povidone-iodine antiseptic, diluted with water), a dropper, a saucer, small samples of foods: bread, potato, rice, apple, cheese, sugar. Adult; iodine stains and must not be swallowed.

Do it: Put a drop of diluted iodine on each food and note the colour.

Why it works: Iodine turns blue-black when it meets starch, because iodine fits inside the coiled starch molecules. Bread, potato and rice turn dark; sugar and cheese stay orange-brown. Throw the samples away afterwards.

31. Compare vitamin C in juices

You need: Iodine solution, cornflour, water, a dropper, clear cups, several fruit juices. Adult.

Do it: Mix a pinch of cornflour into a cup of water, then add iodine drop by drop until it turns dark blue. Pour equal amounts into cups and add one juice to each, a drop at a time, counting the drops needed to make the blue disappear.

Why it works: Vitamin C (ascorbic acid) reacts with iodine and turns it into colourless iodide, so the blue starch colour fades. The fewer drops a juice needs, the more vitamin C it contains. Try fresh juice against juice left open for a few days, because vitamin C breaks down in air.

32. Saliva turns starch sweet

You need: A plain, unsalted cracker.

Do it: Chew the cracker without swallowing for about a minute and notice how the taste changes.

Why it works: Saliva contains amylase, an enzyme that starts breaking starch into smaller sugar molecules, which taste sweet. Digestion begins in the mouth before food reaches your stomach.

33. Make yoghurt

You need: A litre of milk, two tablespoons of live plain yoghurt, a saucepan, a thermometer, a clean jar, a warm place. Adult for heating.

Do it: Heat the milk to about 80 °C, then cool it to about 43 °C. Stir in the yoghurt, pour it into the jar, cover it and keep it warm for 6 to 12 hours.

Why it works: The live yoghurt contains bacteria that turn lactose, the sugar in milk, into lactic acid. The acid makes milk proteins tangle and set into a gel, and gives yoghurt its tangy taste. Use very clean equipment; if it smells off or has coloured patches, throw it away.

34. Hard water and soap suds

You need: Three identical bottles with lids, distilled or rainwater, tap water, Epsom salts (magnesium sulphate), liquid soap (not detergent), a ruler.

Do it: Fill each bottle a third full: one with distilled water, one with tap water, and one with distilled water plus a teaspoon of Epsom salts. Add three drops of soap to each, shake for 10 seconds and measure the height of the suds.

Why it works: Hard water contains dissolved calcium and magnesium ions, which react with soap to form insoluble scum instead of lather. The Epsom salt water makes the fewest suds. Repeat with washing-up liquid: modern detergents are designed not to react this way.

Crystals, mixtures and separations

Crystals grow when dissolved substances come out of solution in an orderly pattern, and mixtures can be separated using differences in their properties (OpenStax Chemistry 2e, chapters 10–11).

35. Rock candy

You need: Two cups of water, four to six cups of sugar, a saucepan, a clean jar, a wooden skewer, a clothes peg. Adult only: boiling sugar causes serious burns.

Do it: Heat the water and stir in sugar until no more dissolves. Let it cool for 20 minutes and pour it into the jar. Wet the skewer, roll it in sugar to seed it, and hang it in the jar from the peg. Leave it undisturbed for a week.

Why it works: Hot water can dissolve far more sugar than cold water. As the solution cools, it holds more sugar than it normally could (it is supersaturated), so sugar molecules come out of solution and build crystals on the seed grains.

36. Salt crystals

You need: Table salt, hot water, a dark plate or saucer, a magnifying glass.

Do it: Dissolve as much salt as you can in a little hot water and pour a thin layer onto the plate. Leave it in a warm place for a few days and examine the crystals.

Why it works: As the water evaporates, the salt can no longer stay dissolved and forms crystals. Sodium chloride crystals are cubes because of the way sodium and chloride ions stack in a regular grid. Compare them with sugar crystals under the magnifier.

37. Epsom salt needles

You need: Epsom salts, hot tap water, a cup, a fridge.

Do it: Stir half a cup of Epsom salts into half a cup of very hot tap water until most of it dissolves. Put the cup in the fridge and check after a few hours.

Why it works: Cooling the solution quickly makes many long, thin crystals grow at once. The shape of a crystal depends on how its particles stack and on how fast it grows. Slow cooling usually gives fewer, larger crystals.

38. Borax crystal snowflakes

You need: Borax (sodium borate), boiling water, a wide jar, pipe cleaners, string, a pencil. Adult only: borax is harmful if swallowed and irritates eyes.

Do it: Twist pipe cleaners into a snowflake shape and tie it to the pencil with string. Dissolve about three tablespoons of borax per cup of boiling water, pour it into the jar and hang the snowflake in it overnight.

Why it works: Borax is much more soluble in hot water than cold. As the solution cools, borax crystallises onto the rough pipe cleaner, which gives the crystals plenty of places to start. Wash your hands afterwards and keep the snowflake away from young children.

39. Grow a stalactite

You need: Two jars, Epsom salts or washing soda, warm water, a length of wool string, two paperclips, a saucer.

Do it: Fill both jars with a strong solution of the salt. Put the jars a hand's width apart with the saucer between them. Weight each end of the string with a paperclip and put one end in each jar so the string sags over the saucer. Leave it for a week.

Why it works: The solution soaks along the string and drips from the lowest point. Each drip leaves a little crystallised salt as water evaporates, slowly building a stalactite, and sometimes a stalagmite below it. Cave formations grow the same way from dissolved calcium carbonate, but over thousands of years.

40. Marker pen chromatography

You need: Coffee filters or kitchen paper, water-based felt-tip pens (especially black and brown), a glass, water, a pencil.

Do it: Cut a strip of paper, draw a thick dot of ink 2 cm from the bottom and hang it so the bottom just touches water in the glass, without the dot going under. Watch for 10 minutes.

Why it works: As water climbs the paper, it carries the dyes in the ink with it. Dyes that dissolve well and stick weakly to the paper travel further, so a single black ink separates into several colours. Chemists use more advanced chromatography to identify substances, including in forensic and drug testing.

41. Leaf pigment chromatography

You need: Fresh spinach or other dark green leaves, a coin, coffee filter strips, rubbing alcohol (isopropyl alcohol), a glass, cling film. Adult: rubbing alcohol is flammable.

Do it: Press a leaf onto a filter strip and roll a coin over it repeatedly to make a dark green line 2 cm from the bottom. Stand the strip in a centimetre of rubbing alcohol, cover the glass and wait 30 to 60 minutes.

Why it works: Leaves contain several pigments: green chlorophylls and yellow-orange carotenoids. They separate as the alcohol carries them up the paper at different speeds. The carotenoids are hidden by chlorophyll in summer and become visible in autumn when the chlorophyll breaks down.

42. Separate salt from sand

You need: A mixture of salt and sand, water, a jug, a coffee filter or kitchen paper in a funnel, a saucepan or shallow dish. Adult if heating.

Do it: Stir the mixture into warm water. Pour it through the filter: the sand stays behind. Leave the salty water in a shallow dish to evaporate in the sun, or have an adult gently boil it off.

Why it works: Salt dissolves in water but sand does not, so filtering separates them. Evaporating the water leaves the salt behind. This is the same principle as traditional sea-salt pans.

43. Oobleck

You need: Two cups of cornflour, about one cup of water, food colouring, a large bowl.

Do it: Mix the cornflour and water slowly until the mixture flows like a liquid when you tilt the bowl. Punch it, then rest your hand gently on it. Squeeze a handful, then open your hand.

Why it works: Oobleck is a shear-thickening fluid: it behaves like a solid when you hit or squeeze it and flows like a liquid when you move gently. Under sudden force, the starch grains jam together and cannot slide past each other. Do not pour it down the sink; throw it in the bin.

44. Slime chemistry

You need: PVA school glue, baking soda, contact lens saline that lists boric acid and sodium borate as ingredients, a bowl. Adult supervision; not for young children.

Do it: Mix half a cup of glue with half a teaspoon of baking soda. Add a tablespoon of contact lens solution and stir, then knead. Add a little more solution if it is too sticky.

Why it works: PVA glue is made of long, flexible polymer chains. Borate ions in the solution link the chains together, turning the runny glue into a stretchy, rubbery material. Wash your hands after playing with it and do not use pure borax powder on skin.

Plants

Plants move water, make food and respond to light and gravity, all of which you can see at home (OpenStax Biology 2e, chapters 8 and 30).

45. Coloured celery

You need: Celery stalks with leaves, or white flowers such as carnations, glasses of water, food colouring, a knife. Adult for cutting.

Do it: Trim the bottom of each stem and stand it in strongly coloured water. Check after a few hours and the next day. Cut across a stem to look at the coloured dots.

Why it works: The dye travels up through xylem, the plant's water-carrying tubes, and colours the leaves or petals. Water is pulled upwards mainly because it evaporates from the leaves, a process called transpiration.

46. Catch a plant's water

You need: A potted plant or a leafy tree branch outdoors, a clear plastic bag, string.

Do it: Tie the bag around a leafy stem on a sunny day and check it after a few hours. Compare with a bag tied around a bare twig.

Why it works: Water droplets collect inside the bag because leaves release water vapour through tiny pores called stomata. A large tree can move hundreds of litres of water from the soil into the air on a hot day.

47. See leaf pores with nail polish

You need: A leaf, clear nail polish, clear sticky tape, a microscope slide, a microscope or a strong phone macro lens.

Do it: Paint a small patch on the underside of a leaf with nail polish and let it dry. Press tape onto it, peel it off and stick it to the slide. Look at it under the microscope.

Why it works: The polish makes a cast of the leaf surface, showing stomata as tiny mouth-shaped openings between pairs of guard cells. Compare the top and bottom of the same leaf: in many plants, most stomata are on the underside, where they lose less water.

48. Bean in a jar

You need: A clear jar, paper towels, water, dried beans (such as broad beans or runner beans).

Do it: Line the jar with damp paper towel and push the beans between the towel and the glass. Keep the towel moist and watch every day.

Why it works: You can watch germination: the seed coat splits, the root grows downwards first, and then the shoot grows upwards. The seed's stored food powers this growth until the leaves can start photosynthesising.

49. What do seeds need to grow?

You need: Cress or mustard seeds, five saucers, cotton wool, water.

Do it: Set up five saucers: one watered in light, one dry, one watered in a dark cupboard, one watered in the fridge, and one in water that completely covers the seeds. Check after a week.

Why it works: Seeds need water, a suitable temperature and oxygen to germinate. Many sprout in the dark, but the seedlings come out pale and leggy because they cannot make chlorophyll without light. Seeds under deep water often struggle because they cannot get enough oxygen.

50. Shoebox plant maze

You need: A shoebox with a lid, card, tape, a sprouting potato or a bean seedling in a small pot, scissors.

Do it: Cut a hole in one end of the box. Tape two or three card partitions inside to make a maze. Put the plant at the far end, close the lid and stand the box with the hole facing a window. Water the plant every few days.

Why it works: The shoot grows around the partitions towards the light. This is phototropism: a plant hormone called auxin builds up on the shaded side of the stem, making those cells grow longer so the stem bends towards the light.

51. Roots that always turn down

You need: The bean-in-a-jar setup with seedlings that have short roots.

Do it: Once the roots are 2 to 3 cm long, turn the jar on its side. Check after a day or two.

Why it works: The roots bend to grow downwards again and the shoots bend upwards. This response to gravity is gravitropism. Special cells in the root tip contain dense starch grains that settle to the bottom of the cell, telling the plant which way is down.

52. Floating leaf discs

You need: Fresh spinach leaves, a drinking straw or hole punch, a 10 ml plastic syringe without a needle, water, baking soda, a drop of washing-up liquid, a clear cup, a bright lamp.

Do it: Dissolve a pinch of baking soda and the drop of washing-up liquid in a cup of water. Punch 10 leaf discs, put them in the syringe with some of the solution, push out the air, cover the tip with your finger and pull the plunger to draw the air out of the leaves. Repeat until the discs sink. Tip them into the cup under the lamp and count how many float every minute.

Why it works: The baking soda supplies carbon dioxide. In the light, the leaf discs photosynthesise, filling their air spaces with oxygen, so they float back up. Move the lamp further away and the discs float more slowly, showing that light drives photosynthesis.

53. Regrow vegetables from scraps

You need: The base of a lettuce, celery or spring onion, a shallow dish of water, a sunny windowsill.

Do it: Stand the base in a few millimetres of water and change the water every day or two. Measure the new growth each day.

Why it works: The base contains meristems, regions of cells that can divide and grow into new leaves. Plants can regrow from pieces in ways most animals cannot, which is why gardeners grow new plants from cuttings.

54. Potato osmosis

You need: A potato, a knife, a ruler or kitchen scale, two cups: one with plain water and one with very salty water. Adult for cutting.

Do it: Cut equal chips of potato and measure their length or mass. Put some in each cup for an hour, then measure them again and feel them.

Why it works: Water moves through cell membranes from where it is more concentrated to where it is less concentrated, a process called osmosis. Chips in plain water absorb water and become firm; chips in salt water lose water and go floppy. This is why salting vegetables draws water out of them.

55. Gummy bear osmosis

You need: Gelatin gummy sweets, three cups: plain water, salt water, sugar water; a ruler.

Do it: Measure the sweets, put one in each cup overnight, and measure them again.

Why it works: The sweet in plain water swells because water moves into the sugary gelatin, where water is less concentrated. In very salty or sugary water it changes much less. Unlike a cell, the gelatin has no membrane, but the idea of water moving from high to low concentration is the same.

56. Shrinking and swelling egg

You need: A "naked egg" from earlier in this list, golden syrup or corn syrup, water, a jar, a kitchen scale.

Do it: Weigh the egg, then leave it in syrup overnight. Weigh it again, then put it in water overnight and weigh it once more.

Why it works: The egg's membrane lets water through but not large sugar molecules. In syrup, water moves out of the egg and it shrivels. In plain water, water moves back in and it swells. Your cells face the same problem, which is why medical drips use saline with the right concentration.

57. Pine cones that open and close

You need: Dry, open pine cones, a bowl of water.

Do it: Soak a pine cone in water for an hour, then leave it to dry in a warm room. Photograph it at each stage.

Why it works: The scales close when wet and open when dry. Each scale has two layers that absorb water differently, so they bend like a bimetallic strip. The tree benefits because seeds are released in dry weather, when the wind can carry them further. No living cells are needed; the movement is purely physical.

Microbes, yeast and decomposition

Microorganisms are too small to see, but you can see what they do (OpenStax Microbiology).

58. Yeast balloons

You need: Three small bottles, three balloons, dried yeast, warm water, sugar, salt.

Do it: Put a teaspoon of yeast and half a cup of warm water in each bottle. Add two teaspoons of sugar to one, sugar and salt to another, and nothing to the third. Cover each with a balloon and compare them after 30 to 60 minutes.

Why it works: Yeast is a living fungus. When it feeds on sugar without enough oxygen, it ferments it and releases carbon dioxide, which inflates the balloon. The bottle with no sugar makes little gas, and a lot of salt slows the yeast down. This gas is what makes bread rise.

59. Find yeast's favourite temperature

You need: Four bottles, four balloons, dried yeast, sugar, water at about 5, 20, 40 and 70 °C, a thermometer. Adult for hot water.

Do it: Set up the bottles as in the previous experiment, with the same amount of yeast and sugar but water at different temperatures. Measure the balloons' circumference every 15 minutes.

Why it works: Yeast works fastest at warm temperatures, around body temperature, and slowly in the cold. Very hot water kills the yeast, so that balloon stays flat. Enzymes in all living things have a temperature range where they work best.

60. Bread mould in sealed bags

You need: Slices of bread, zip-lock bags, sticky tape, a marker, a little water.

Do it: Put slices in separate bags under different conditions: dry, damp, in the fridge, in a warm cupboard, wiped on a kitchen surface. Seal every bag, tape it shut and observe it through the plastic for a week or two.

Why it works: Mould spores are everywhere in the air. Mould grows fastest when it is warm and damp and slowest when it is cold or dry, which is why refrigeration and drying preserve food. Never open the bags. Throw them away sealed, and skip this experiment if anyone in your home has allergies or asthma.

61. Glitter germs

You need: Hand lotion or cooking oil, fine glitter, soap, water, paper towels.

Do it: Rub a little lotion on your hands and sprinkle on glitter, the "germs". Shake hands with someone or touch objects and see where the glitter ends up. Then try rinsing with water only, and then washing properly with soap for 20 seconds.

Why it works: The glitter shows how easily germs spread by touch. Water alone removes little of it; soap and scrubbing work much better because soap lifts oils, and the germs stuck in them, off the skin (CDC).

62. Start a sourdough starter

You need: Wholemeal or rye flour, water, a clean jar, a loose lid or cloth, a rubber band to mark the level.

Do it: Mix equal weights of flour and water, cover loosely and leave at room temperature. Each day, discard half and feed it with fresh flour and water. Mark the level after each feed and see how high it rises.

Why it works: Flour carries wild yeasts and lactic acid bacteria. Feeding them selects for the microbes that thrive in this environment, and after one to two weeks the starter rises reliably, producing carbon dioxide and acids that give sourdough its flavour. Discard it if you see pink, orange or furry mould.

63. Compost in a bottle

You need: A large clear plastic bottle with the top cut off, soil, vegetable peelings, dry leaves, shredded newspaper, water, a spray bottle. Adult for cutting.

Do it: Layer soil, peelings, leaves and paper, spray each layer lightly with water and cover the top loosely. Keep it damp, mix it once a week and record changes over six weeks.

Why it works: Bacteria, fungi and small animals break dead material down into simpler substances, releasing nutrients that plants can use. Decomposition recycles matter through ecosystems. Green, nitrogen-rich peelings and brown, carbon-rich leaves both help.

64. What breaks down in soil?

You need: A patch of garden or a large pot of soil, items to test (an apple core, a paper towel, a cotton rag, a plastic bag, a crisp packet, a "compostable" bag), labels.

Do it: Bury each item about 10 cm deep and mark the spot. Dig them up after four and eight weeks and compare them with photos taken at the start.

Why it works: Microbes can digest natural materials such as fruit, paper and cotton, so these break down. Most plastics are not food for microbes, so they barely change. Many "compostable" plastics are designed for the heat of industrial composting and may change little in a cool garden.

The human body

Your body is the most convenient specimen you have. These experiments explore its cells, senses and systems (OpenStax Anatomy and Physiology 2e).

65. Extract DNA from strawberries

You need: Two or three strawberries, a zip-lock bag, a teaspoon of washing-up liquid, half a teaspoon of salt, half a cup of water, a coffee filter, a glass, ice-cold rubbing alcohol (isopropyl, 70 percent or stronger), a wooden skewer. Adult: rubbing alcohol is flammable.

Do it: Mash the strawberries in the bag with the water, salt and washing-up liquid for two minutes. Filter the mixture into the glass. Slowly pour an equal amount of cold rubbing alcohol down the side so it floats on top. Wait a few minutes and lift out the white strands with the skewer.

Why it works: The soap breaks open cell and nuclear membranes, and the salt helps DNA strands clump together. DNA does not dissolve in alcohol, so it comes out of solution as visible white threads. Strawberries work well because each cell has eight copies of each chromosome.

66. Extract DNA from your cheek cells

You need: Salty water or a sports drink, a small clear glass, washing-up liquid, ice-cold rubbing alcohol, a pinch of meat tenderiser powder (optional). Adult.

Do it: Swish a tablespoon of salty water around your mouth for 30 seconds and spit it into the glass. Add a drop of washing-up liquid and the tenderiser, swirl gently, then slowly add the same volume of cold alcohol on top. Wait a few minutes.

Why it works: Swishing collects loose cheek cells. The soap breaks them open, and the tenderiser contains enzymes that break down proteins wrapped around the DNA. Your DNA gathers as white wisps at the boundary with the alcohol. You are looking at many millions of copies of your own genome clumped together.

67. Measure your lung capacity

You need: A large plastic bottle (at least 3 litres), a measuring jug, a washing-up bowl, flexible tubing, a marker pen.

Do it: Mark the bottle in 250 ml steps using the jug. Fill it with water, put your hand over the top and turn it upside down in the half-full bowl. Push the tube inside, take a deep breath and blow out as much as you can through the tube. Read how much water you displaced.

Why it works: The air you breathe out pushes out the same volume of water. This measures roughly your vital capacity: the largest volume of air you can exhale after the deepest breath. It depends on height, age, sex and fitness. Use a fresh mouthpiece for each person.

68. Model lung with balloons

You need: A small plastic bottle with the bottom cut off, two balloons, a straw, modelling clay, tape. Adult for cutting.

Do it: Put a balloon on the end of the straw and push it through the bottle neck, sealing the gap with clay. Cut the second balloon in half and stretch it over the open bottom of the bottle. Pull the bottom balloon down, then push it up.

Why it works: Pulling the "diaphragm" down increases the space inside the bottle, lowering the air pressure, so air rushes into the "lung" balloon. Your diaphragm muscle does the same thing every time you breathe in.

69. Pulse and exercise

You need: A timer, a notebook.

Do it: Find your pulse on your wrist or neck and count the beats for 30 seconds while resting; double it to get beats per minute. Do one minute of jumping jacks and measure again, then every minute afterwards until it returns to normal.

Why it works: During exercise your muscles need more oxygen and produce more carbon dioxide, so your heart beats faster to move blood more quickly. Fitter people usually recover to their resting rate faster. If you feel unwell during exercise, stop.

70. Find your blind spot

You need: A white card, a pen.

Do it: Draw a cross and, about 8 cm to its right, a dot. Hold the card at arm's length, close your left eye and stare at the cross with your right eye. Slowly bring the card closer until the dot vanishes.

Why it works: Where the optic nerve leaves the back of your eye there are no light-sensitive cells, so part of the image falls on a spot that cannot see. Your brain normally fills in the gap so smoothly that you never notice.

71. Taste needs smell

You need: Jelly beans or fruit sweets in different flavours, a blindfold.

Do it: Blindfolded and holding your nose, eat a sweet and try to name its flavour. Then let go of your nose while it is still in your mouth.

Why it works: Your tongue can detect only sweet, salty, sour, bitter and umami. Most of what we call flavour comes from smell, as aroma molecules travel from the back of your mouth into your nose. When you let go, the flavour suddenly appears. This is also why food tastes bland when you have a cold.

72. Two-point touch test

You need: Two cocktail sticks or a paperclip bent into a U shape, a ruler, a partner.

Do it: With your partner's eyes closed, touch their skin gently with either one or two points. Find the smallest gap at which they can tell there are two points, on the fingertip, palm, forearm and back.

Why it works: Your fingertips are packed with touch receptors, and a large area of your brain processes signals from them, so you can tell two points apart only a few millimetres apart. On your back, receptors are much more spread out, so the points need to be several centimetres apart.

73. Classify your fingerprints

You need: A soft pencil, clear sticky tape, white paper, a magnifying glass.

Do it: Rub pencil onto a patch of paper, roll your fingertip in it, then press sticky tape onto your finger and stick it onto white paper. Compare all ten fingers and those of family members.

Why it works: Fingerprints are usually classified as loops, whorls or arches. Loops are the most common pattern. The pattern forms before birth and is influenced by both genes and conditions in the womb, so even identical twins have different prints.

74. Find your dominant eye

You need: Your hands and a distant object.

Do it: Make a small triangle with your hands at arm's length and look through it at a distant object with both eyes open. Close your left eye, then your right. Whichever eye keeps the object in the triangle is your dominant eye.

Why it works: The brain combines images from both eyes but tends to rely more on one of them for aiming and judging position. Eye dominance is not always on the same side as your dominant hand, which matters in sports such as archery and shooting.

75. Afterimages

You need: A brightly coloured image (such as a red, green or blue shape) on white paper, a plain white sheet.

Do it: Stare at the centre of the coloured shape for 30 seconds without moving your eyes, then quickly look at the white paper.

Why it works: You see a ghost of the shape in the opposite colour. The cells in your retina that respond to the original colour become temporarily less sensitive, so when you look at white, the other colour signals dominate for a few seconds.

76. Colour at the edge of your vision

You need: Coloured pens, a partner.

Do it: Stare straight ahead at a fixed point. Have your partner slowly move a pen from behind your head into the side of your vision. Note when you can see something moving, and when you can tell what colour it is.

Why it works: You notice movement long before you can name the colour. Colour-detecting cells (cones) are concentrated in the centre of the retina, while rods, which are sensitive to dim light and movement, dominate at the edges.

77. Pupil reflex

You need: A mirror, a room you can darken, a torch.

Do it: Sit in a dim room for a minute, then look at your eyes in the mirror and switch on a light. Never shine a bright light directly into anyone's eyes.

Why it works: Your pupils shrink in bright light and widen in the dark, automatically and within a second. This reflex controls how much light reaches the retina. Doctors check it to test whether nerves and parts of the brain are working properly.

78. Knee-jerk reflex

You need: A chair high enough to let your legs dangle, a partner, the side of a hand.

Do it: Sit with your legs dangling. Your partner taps gently just below your kneecap with the side of their hand.

Why it works: Tapping the tendon stretches the thigh muscle, and a signal travels to your spinal cord and straight back to the muscle, which contracts and kicks your leg. The message does not have to go through your brain first, which is why reflexes are so fast.

Earth science

Soil, rock and water shape the land over timescales from minutes to millions of years (USGS; OpenStax Biology 2e, chapter 46).

79. Soil shake test

You need: A tall clear jar with a lid, garden soil, water, a drop of washing-up liquid, a ruler.

Do it: Fill the jar a third full with soil, add water almost to the top and the washing-up liquid. Shake hard for a few minutes and leave it to settle. Measure the layers after one minute, one hour and one day.

Why it works: Particles settle by size: sand drops within a minute, silt within hours, and fine clay can take a day or more. The thickness of each layer tells you your soil's texture, which affects how well it drains and holds nutrients.

80. Erosion trays

You need: Two baking trays or shallow boxes, soil, a patch of turf or grass seedlings, a watering can, books to tilt the trays, two bowls.

Do it: Fill one tray with bare soil and one with soil covered by grass. Tilt both and pour the same amount of water onto each from the same height, catching the runoff in bowls.

Why it works: The runoff from bare soil is muddy because raindrops and flowing water carry soil away. Roots hold soil in place and leaves soften the impact of the rain. This is why farmers plant cover crops and why deforested hillsides are prone to landslides.

81. Model volcano

You need: A small bottle, modelling clay or papier-mâché, baking soda, vinegar, washing-up liquid, red food colouring, a tray.

Do it: Build a cone around the bottle. Put two tablespoons of baking soda, a squirt of washing-up liquid and some colouring inside, then pour in vinegar.

Why it works: The foam comes from carbon dioxide made by the reaction. It is a fun model, but be honest about its limits: real eruptions are driven by gases such as water vapour and carbon dioxide that were dissolved in molten rock under pressure and expand as magma rises. Shaking a fizzy drink and opening it is a better model of that.

82. Cracker plate tectonics

You need: Two biscuits or crackers, a plate of thick icing or peanut butter, water.

Do it: Lay the crackers side by side on the icing. Push them together, slide them past each other and pull them apart. Then dip the edges of one cracker in water and push the pair together again.

Why it works: The crackers are tectonic plates floating on the soft, slowly flowing mantle. Pulling apart makes a gap like a mid-ocean ridge, sliding shows a transform fault, and pushing a wet, softened edge into a dry one crumples it into a "mountain range", as when India pushed into Asia.

83. Crayon rock cycle

You need: Old crayons, a pencil sharpener or grater, foil, a heavy book, warm water, an oven or hot plate. Adult for heat.

Do it: Shave crayons into layers on foil (sediment). Fold the foil and press it with the book to make "sedimentary rock". Warm the parcel in hot water and press again ("metamorphic rock"). Finally have an adult melt some shavings completely and let them cool ("igneous rock").

Why it works: Real rocks change form in the same three ways: sediments are compacted and cemented, heat and pressure transform existing rocks without melting them, and melted rock cools into new crystals. The rock cycle takes millions of years.

84. Make fossil imprints

You need: Modelling clay or salt dough, shells, leaves or small plastic animals, plaster of Paris, a paper cup. Adult for mixing plaster.

Do it: Press an object into flattened clay and remove it. Pour plaster into the imprint and let it set, then peel away the clay.

Why it works: The imprint is a mould and the plaster is a cast, the two main ways fossils preserve shape. Many fossils form when a buried shell dissolves and leaves a hollow mould that minerals later fill.

85. Mineral hardness test

You need: Rock and mineral samples (from a garden, beach or kit), your fingernail, a copper coin, a steel nail.

Do it: Try to scratch each sample with your fingernail, then the coin, then the nail. Note which ones scratch and which do not.

Why it works: The Mohs scale ranks minerals by which can scratch which, from talc (1) to diamond (10). A fingernail is about 2.5, a copper coin about 3 to 3.5 and a steel nail about 5.5. Quartz, at 7, will scratch steel. Geologists use this quick test to help identify minerals in the field.

86. Aquifer in a cup

You need: A clear cup, gravel, sand, clay or modelling clay, water, food colouring, a straw.

Do it: Layer gravel at the bottom, a layer of clay over half of it, and sand on top. Pour in water and watch where it collects. Put the straw into the gravel and suck gently to "pump" groundwater. Then drip colouring onto the surface as "pollution".

Why it works: Water soaks through sand and gravel and is stored in the gaps between grains, an aquifer. Clay slows it down. The colouring shows how pollutants on the surface can seep into groundwater that people drink (USGS).

Weather and climate

Simple instruments let you measure the weather, and models help explain the climate (NOAA).

87. Rain gauge

You need: A straight-sided clear plastic bottle, scissors, a ruler, tape, pebbles. Adult for cutting.

Do it: Cut off the top of the bottle and turn it upside down into the base as a funnel. Put pebbles in the bottom, add water to just above them and tape a ruler to the side, with zero at the water level. Put it outside in the open and read it every day at the same time.

Why it works: A straight-sided gauge collects the same depth of rain as falls on flat ground, whatever its width. Comparing your readings with your local weather service is a good test of your gauge. Volunteer networks such as CoCoRaHS collect readings like this for scientists (CoCoRaHS).

88. Balloon barometer

You need: A glass jar, a balloon, a rubber band, a straw, tape, a card marked with a scale.

Do it: Cut the neck off the balloon, stretch it tightly over the jar and secure it with the rubber band. Tape the straw on top so it sticks out sideways like a pointer. Stand the card behind the straw and mark where it points each day. Keep the jar indoors, away from sunlight and heaters.

Why it works: When outside air pressure rises, it pushes the balloon down and the straw tip rises; when it falls, the balloon bulges and the pointer drops. Falling pressure often means unsettled weather is coming. Temperature changes also affect the jar, which is why it must stay in one place.

89. Cup anemometer

You need: Five paper cups, two straws, a pin, a pencil with an eraser, tape, a marker. Adult for the pin.

Do it: Tape four cups to the ends of two crossed straws, all facing the same way round. Pin the centre to the pencil eraser and stand the pencil in the fifth cup weighted with sand. Mark one cup and count its turns per minute outside.

Why it works: Wind pushes harder on the open side of each cup than on the rounded back, so the anemometer spins faster in stronger wind. Count the turns on different days to compare wind speeds.

90. Water cycle in a bag

You need: A zip-lock bag, water, blue food colouring, a marker, tape, a sunny window.

Do it: Draw clouds, sun and sea on the bag, add a quarter cup of coloured water, seal it and tape it to the window. Check it several times a day.

Why it works: Sunlight warms the water, which evaporates. The vapour cools at the top of the bag, condenses into droplets ("clouds") and trickles back down ("rain"). The colouring stays in the water below, just as salt stays in the sea when seawater evaporates.

91. Tornado in a bottle

You need: Two identical plastic bottles, water, strong tape or a tornado tube connector, glitter.

Do it: Fill one bottle two-thirds full with water and glitter, tape the second bottle upside down on top, and turn them over. Swirl the top bottle quickly in a circle and watch.

Why it works: Swirling sets the water spinning, and it forms a vortex as it drains, with a funnel of air in the middle. Spinning water moves faster as it moves inward, just as an ice skater spins faster when pulling in their arms. Real tornadoes form in a very different way, from rotating thunderstorms, but share the vortex shape.

92. Why a closed jar warms up

You need: Two identical jars, two thermometers, a lid or cling film, a sunny spot or a lamp.

Do it: Put a thermometer in each jar, cover only one, and stand both in sunlight. Record the temperatures every five minutes for half an hour.

Why it works: The covered jar gets warmer. This is often called a greenhouse-effect model, but it mainly works because the lid stops warm air from escaping and mixing with cooler air. The real greenhouse effect is different: gases such as carbon dioxide absorb heat radiated by Earth and send some back down (NASA). Spotting the difference is part of the experiment.

93. Sea ice vs land ice

You need: Two identical clear containers, ice cubes, modelling clay or stones, water, a marker.

Do it: In one container, float ice cubes in water. In the other, build a "continent" of clay and put the same number of ice cubes on it, then add water to the same level as the first. Mark both water levels and wait for the ice to melt.

Why it works: Floating ice already displaces its own weight of water, so when it melts the level barely changes. Ice resting on land adds new water to the sea when it melts, so the level rises. That is why melting ice sheets on Greenland and Antarctica raise sea levels, while melting Arctic sea ice does not directly.

Environmental science

These experiments show how pollution spreads and how we can clean it up.

94. Oil spill clean-up

You need: A tray of water, cooking oil, a feather, and clean-up tools: cotton wool, a sponge, paper towel, a spoon, washing-up liquid.

Do it: Pour a spoonful of oil onto the water. Try each tool and time how long it takes to remove the oil. Dip the feather in the oily water and try to clean it.

Why it works: Oil floats and spreads into a thin film that is hard to collect. Absorbent materials soak up some of it, and detergent breaks it into droplets, which removes it from the surface but spreads it through the water. The oily feather shows why spills are so harmful to seabirds: oil destroys the waterproofing and insulation of their feathers.

95. Build a water filter

You need: A plastic bottle cut in half, cotton wool or a coffee filter, fine sand, coarse sand, gravel, muddy water. Adult for cutting.

Do it: Turn the top half upside down into the bottom half. Layer cotton wool, fine sand, coarse sand and gravel. Pour muddy water in and compare what comes out with what went in.

Why it works: The layers trap particles of decreasing size. Water treatment plants use sand filters as one step. Do not drink the water: filtering removes dirt but not dissolved chemicals or germs, which is why treatment works also disinfect water.

96. Air pollution catcher

You need: White cards, petroleum jelly, string, a magnifying glass.

Do it: Smear jelly on several cards and hang them in different places: by a road, in a garden, indoors, near a kitchen. Collect them after a week and compare the specks under the magnifier.

Why it works: Particles in the air stick to the jelly. Cards near traffic or cooking usually collect more. The finest particles, which affect health most, are too small to see, so this shows only larger particles. Air-quality monitors measure fine particles directly.

The sky

You do not need a telescope to do real astronomy. These experiments use your eyes, a notebook and patience (OpenStax Astronomy 2e).

97. Shadow clock

You need: A stick, a sunny patch of flat ground or a sheet of card, small stones, a watch.

Do it: Stand the stick upright. Every hour, mark the tip of its shadow with a stone and note the time. Try it again a month later.

Why it works: The shadow moves as Earth rotates, and it is shortest around midday, when the Sun is highest. The line of shortest shadow points roughly north-south. Over the year the midday shadow gets longer and shorter as the Sun's height changes with the seasons.

98. Track the sunset

You need: A fixed spot with a view of the western horizon, a notebook or camera.

Do it: Once a week at sunset, note or photograph where the Sun goes down relative to buildings or trees. Keep it up for a few months.

Why it works: The sunset point moves along the horizon: furthest north around the June solstice and furthest south around the December solstice. This is because Earth's axis is tilted. Ancient monuments such as Stonehenge are aligned with these solstice positions.

99. Moon diary

You need: A notebook, clear evenings over a month.

Do it: Each evening, draw the Moon's shape and note the time and its direction in the sky.

Why it works: You will see the Moon go through its phases in about 29.5 days and rise about 50 minutes later each night on average. The phases happen because we see different amounts of the Moon's sunlit half as it orbits Earth. It is not caused by Earth's shadow.

100. Count stars to measure light pollution

You need: A clear, moonless night, a star chart for the constellation Orion or another bright constellation.

Do it: After your eyes adjust to the dark for 15 minutes, compare how many stars you can see with the reference charts on the Globe at Night website, then submit your result (Globe at Night).

Why it works: Artificial light scatters in the atmosphere and brightens the sky, hiding fainter stars. Counting stars is a simple measure of sky brightness, and data from thousands of volunteers helps scientists track how light pollution changes over time.

101. Spot the International Space Station

You need: NASA's Spot the Station website to find sighting times for your location (NASA).

Do it: Go outside a few minutes before a listed pass and look in the given direction. Time how long it takes to cross the sky.

Why it works: The station has no lights you can see from the ground; it shines because it reflects sunlight. Passes happen just after sunset or before sunrise, when you are in darkness but the station, about 400 kilometres up, is still in sunlight. It circles Earth roughly every 90 minutes.

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References

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