101 Best Physics Experiments You Can Do at Home

You do not need a laboratory to see physics in action. A glass of water, a balloon, a torch and a few coins can demonstrate inertia, air pressure, refraction and static electricity. This list gives you 101 physics experiments you can do at home, grouped by topic. Each one lists what you need, what to do, and why it works.

Most take under 30 minutes and use things already in a typical kitchen or drawer. They suit curious students, parents, home educators and teachers looking for demonstrations. Where an experiment needs heat, sharp tools, a microwave or strong magnets, it is marked for adult supervision.

About this list. These are well-established classroom and science-museum demonstrations, adapted for home materials. We describe what normally happens and why, based on the physics in the OpenStax textbooks and activity collections from the Exploratorium and the Institute of Physics (see References). We did not run each one for this article, and results vary with materials, so if something does not work the first time, change one thing and try again. That is what experimenting is.

Safety first

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

• An adult should be present for anything marked Adult, which includes all experiments with flames, boiling water, the microwave, the oven or sharp tools.
• Never use mains electricity. Every electrical experiment here uses ordinary AA or AAA batteries. Do not use coin cells or lithium batteries for circuits, and never short-circuit any battery for longer than a moment; wires and batteries can get hot.
• Keep small magnets and button batteries away from young children. Swallowing them can cause serious internal injuries.
• Never look at the Sun, even through sunglasses. Use only the indirect methods described.
• Never shine a laser pointer at anyone's eyes, or at mirrors or shiny surfaces facing people.
• Do not eat or drink anything used in an experiment, and wash your hands afterwards.
• Work outside for anything that could spill, splash or fly.

How to get more out of each experiment

A demonstration becomes an experiment when you change one thing on purpose and measure what happens. For any activity below:

1. Predict first. Write down what you think will happen and why.
2. Change one variable at a time, such as height, length, temperature or mass, and keep everything else the same.
3. Measure, don't just watch. Use a ruler, a kitchen scale, a timer or a phone camera in slow motion.
4. Repeat each trial at least three times and take the average, because single results can be flukes.
5. Explain any surprises. A result that disagrees with your prediction is the most interesting kind.

When you want to go further, our list of 101 physics projects for students turns many of these ideas into full investigations.

Forces and motion

These experiments show Newton's laws, friction, gravity and air resistance (OpenStax College Physics 2e, chapters 2–5).

1. Coin, card and glass

You need: A glass, a playing card or postcard, a coin.

Do it: Lay the card over the glass and put the coin in the middle of the card. Flick the card sharply sideways with your finger.

Why it works: The card shoots away, and the coin drops straight into the glass. The coin's inertia keeps it in place, and the flick is too quick for friction to drag it along. This is Newton's first law.

2. Paper pull from under a cup

You need: A strip of smooth paper, a plastic cup half full of water.

Do it: Put the cup on the paper near the edge of a table. Pull the paper slowly, then try again with a fast, sharp tug.

Why it works: A slow pull drags the cup with it; a fast tug leaves it behind. The force of friction acts for so short a time that it cannot give the cup much momentum. It is a safer version of the tablecloth trick.

3. Flat paper vs crumpled paper

You need: Two identical sheets of paper.

Do it: Crumple one sheet into a ball. Drop both from the same height at the same moment.

Why it works: The ball lands first, even though the sheets have the same mass. The flat sheet has a much larger area, so air resistance slows it more. Gravity pulls both equally.

4. Book and paper drop

You need: A hardback book, a sheet of paper smaller than the book.

Do it: Drop the book and the paper side by side. Then lay the paper on top of the book and drop them together.

Why it works: On its own, the paper drifts down slowly. On top of the book, the book pushes the air out of the way and the paper falls with it at the same rate. Without air resistance, all objects fall with the same acceleration.

5. Ruler-drop reaction time

You need: A 30 cm ruler, a partner.

Do it: Your partner holds the ruler vertically with the zero mark between your open finger and thumb, then drops it without warning. Catch it and read the distance it fell.

Why it works: The ruler falls with constant acceleration, so distance tells you time: $t = \sqrt{2d/g}$. A catch at 20 cm means a reaction time of about 0.20 seconds. Try it tired, distracted or with your other hand.

6. Balloon rocket

You need: A balloon, a drinking straw, a long piece of string, sticky tape.

Do it: Thread the string through the straw and tie it tight between two chairs. Blow up the balloon, hold the neck shut, tape it to the straw and let go.

Why it works: The balloon pushes air out of the back, and the air pushes the balloon forward. This is Newton's third law, the same principle that drives real rockets. Compare round and long balloons.

7. Balloon-powered car

You need: A small cardboard box or plastic bottle, four bottle-cap wheels, two wooden skewers, two straws, a balloon, tape. Adult help to make holes.

Do it: Fix the straws across the body as axle holders, push the skewers through and attach the caps as wheels. Tape a balloon to a straw pointing backwards, blow it up through the straw and release.

Why it works: Air rushing backwards gives the car forward momentum. Friction in the axles and the floor slows it down, so the best designs are light and have free-spinning wheels.

8. Marble Newton's cradle

You need: A ruler with a groove down the middle, five identical marbles.

Do it: Line up four marbles touching in the groove. Roll the fifth into them. Then roll two together.

Why it works: One marble in sends one marble out the far end; two in sends two out. Both momentum and kinetic energy are nearly conserved, and the only way to satisfy both is for the same number of marbles to leave.

9. Stacked ball bounce

You need: A basketball, a tennis ball. Do this outside.

Do it: Hold the tennis ball directly on top of the basketball and drop them together onto hard ground.

Why it works: The tennis ball rockets up far higher than it was dropped from. The basketball bounces first and then hits the still-falling tennis ball, transferring momentum and energy to the lighter ball. Keep faces away from the top.

10. Ramp height and speed

You need: A board or large book as a ramp, a toy car, a tape measure, a stack of books.

Do it: Release the car from different heights on the ramp and measure how far it rolls across the floor.

Why it works: Higher starting points give the car more gravitational potential energy, which becomes kinetic energy at the bottom. Friction and air resistance then turn it into heat as the car slows.

11. Rubber-band friction meter

You need: A shoe, a rubber band, a ruler, different surfaces such as a carpet, a tiled floor and a towel.

Do it: Loop the band around the shoe and pull gently until it starts to slide. Measure how far the band stretches. Repeat on each surface.

Why it works: A longer stretch means a larger force, so more friction. You will usually see a bigger stretch just before the shoe moves than while it slides, showing that static friction is larger than kinetic friction.

12. Inseparable books

You need: Two paperback books or notebooks.

Do it: Interleave the pages one by one, so each page overlaps a page from the other book. Try to pull the books apart by their spines.

Why it works: Each page contact provides only a little friction, but hundreds of overlapping pages add up to a surprisingly large force. Pulling also squeezes the pages together, increasing the friction further.

13. Find the centre of mass of a shape

You need: A piece of card cut into an irregular shape, a pin, a string with a small weight (a plumb line), a pencil.

Do it: Hang the card loosely from a pin near one edge, hang the plumb line from the same pin and trace the line. Repeat from two other points.

Why it works: A freely hanging object settles with its centre of mass directly below the pivot. The lines cross at the centre of mass. Check by balancing the card on a pencil tip at that point.

14. The balancing fork and spoon

You need: A fork, a spoon, a toothpick, a glass.

Do it: Wedge the spoon into the fork's prongs so they form a V. Push the toothpick between the prongs and rest its tip on the rim of the glass. Adjust until it balances.

Why it works: The heavy cutlery hangs below the rim, bringing the combined centre of mass below the pivot point. Anything balances when its centre of mass sits directly below or above the support.

15. Pendulum period

You need: String, a weight such as a nut or a key, tape, a stopwatch.

Do it: Hang the weight from a table edge. Time 10 small swings at different string lengths, then with different weights.

Why it works: For small swings the period depends on the length, not the mass. Quadrupling the length doubles the period, as $T = 2\pi\sqrt{L/g}$ predicts. Timing 10 swings and dividing reduces timing error.

16. Coupled pendulums

You need: Two identical pendulums hanging from the same loose string stretched between two chairs.

Do it: Start one pendulum swinging and hold the other still, then let go.

Why it works: Energy passes through the connecting string. Over a few swings the first pendulum slows down while the second starts swinging, then the energy flows back. This is resonance: both have the same natural frequency.

17. Raw or boiled egg?

You need: A raw egg and a hard-boiled egg.

Do it: Spin each on a plate. Then touch each spinning egg briefly to stop it and let go at once.

Why it works: The boiled egg spins smoothly because it is solid. The raw egg wobbles, and after you stop it, it starts turning again: the liquid inside kept moving because of its inertia and drags the shell back into motion.

18. Water bucket swing

You need: A small bucket with a sturdy handle, some water. Do this outside.

Do it: Swing the bucket quickly in a full vertical circle at arm's length.

Why it works: At the top of the circle, the water stays in because the bucket is accelerating downwards towards the centre at least as fast as gravity would pull the water. Swing too slowly and you get wet.

19. Spinning chair and books

You need: A swivel office chair, two heavy books, a helper. Adult spotter.

Do it: Sit holding the books at arm's length while someone gently spins the chair. Pull the books in to your chest, then push them out again.

Why it works: Pulling the books in lowers your moment of inertia, so you spin faster to conserve angular momentum. Figure skaters use the same trick. Stop if you feel dizzy.

20. Paper helicopter

You need: A strip of paper, scissors, a paperclip.

Do it: Cut the top half of the strip down the middle and fold the two flaps in opposite directions. Add a paperclip at the bottom and drop it from a height.

Why it works: Air pushing on the angled blades makes it spin, and the spinning blades create drag that slows the fall. Try longer blades or more paperclips and time the drop.

21. Paper aeroplane test

You need: Paper, a tape measure.

Do it: Fold three different designs and throw each five times with the same effort. Measure the average distance.

Why it works: Flight depends on lift, drag, weight and thrust. Wing area, the position of the centre of mass and the wing angle all change how far it glides. A paperclip on the nose moves the centre of mass forward and often stabilises a design that stalls.

Air pressure and fluids

These show air pressure, density, buoyancy and surface tension (OpenStax College Physics 2e, chapters 11–12).

22. Upside-down glass of water

You need: A glass filled to the brim with water, a piece of stiff card. Do this over a sink.

Do it: Put the card on top, press it down, and turn the glass upside down while holding the card. Let go of the card.

Why it works: The card stays on and the water stays in. Air pressure pushing up on the card is much greater than the weight of the water pushing down, and surface tension helps seal the edge.

23. Crushing can

You need: An empty drinks can, a tablespoon of water, a pan, tongs, a bowl of cold water. Adult only: hot steam.

Do it: Heat the can with the water inside on a hob until steam comes out. Using tongs, quickly turn it upside down into the cold water.

Why it works: The can crumples with a bang. Steam pushed most of the air out; the cold water condenses the steam, the pressure inside drops sharply, and air pressure outside crushes the can.

24. Egg into a bottle

You need: A glass bottle with a neck slightly narrower than a peeled hard-boiled egg, very hot water. Adult only.

Do it: Pour hot water into the bottle, swirl it to warm the glass and pour it out. Immediately sit the egg on the neck.

Why it works: As the air inside cools, its pressure drops, and the higher outside air pressure pushes the egg into the bottle. To get it out, tip the bottle upside down and blow in hard so higher inside pressure pushes it out.

25. Blow between two sheets of paper

You need: Two sheets of paper.

Do it: Hold them hanging down, a few centimetres apart, and blow hard between them.

Why it works: You might expect them to fly apart, but they come together. The fast-moving air between them is at lower pressure than the still air outside, which pushes them inwards.

26. Floating ball in a hairdryer stream

You need: A hairdryer on the cool setting, a ping-pong ball.

Do it: Point the hairdryer upwards and place the ball in the airstream. Slowly tilt the dryer.

Why it works: The ball hovers, and it stays in the stream even when tilted. If it drifts to the edge, the airflow curving around it pushes it back towards the centre.

27. Cartesian diver

You need: A clear plastic bottle full of water, a ketchup sachet or a pen lid with a blob of modelling clay to make it just float.

Do it: Put the diver in, screw the cap on tight and squeeze the bottle.

Why it works: The diver sinks when you squeeze and rises when you let go. Squeezing compresses the air bubble inside the diver, so it displaces less water and becomes denser than water. That is buoyancy in action.

28. Floating egg

You need: A raw egg, a tall glass of water, salt.

Do it: Put the egg in plain water, where it sinks. Take it out, stir in several spoonfuls of salt, and put it back.

Why it works: Salt water is denser than fresh water. Once it is denser than the egg, the buoyant force exceeds the egg's weight and it floats. Carefully pour fresh water on top and the egg will hover in the middle.

29. Density tower

You need: A tall glass, honey, washing-up liquid, water with food colouring, vegetable oil.

Do it: Pour each liquid in slowly, in that order, down the side of the glass. Then drop in small objects such as a grape, a cork and a coin.

Why it works: The liquids layer from densest at the bottom to least dense at the top. Each object sinks until it reaches a layer denser than itself.

30. Homemade lava lamp

You need: A clear bottle, vegetable oil, water, food colouring, an effervescent tablet.

Do it: Fill the bottle three-quarters with oil and top it up with coloured water. Drop in a piece of tablet.

Why it works: Water sinks below the oil because it is denser, and the two do not mix. The tablet releases gas bubbles that carry blobs of water upwards; at the top the gas escapes and the water sinks again.

31. Clay boat challenge

You need: Modelling clay, a bowl of water, coins or marbles.

Do it: Drop a ball of clay in the water and watch it sink. Then shape the same clay into a boat and see how many coins it can carry.

Why it works: Shaping the clay into a hull lets it displace much more water. By Archimedes' principle, the upward buoyant force equals the weight of water displaced, which is how steel ships float.

32. Volume by displacement

You need: A measuring jug, water, an irregular object such as a stone, a kitchen scale.

Do it: Note the water level, submerge the object and read the new level. Weigh the object.

Why it works: The rise in water level equals the object's volume. Divide its mass by its volume to find its density, and compare it with known values for stone, glass or metal.

33. Water jets at different heights

You need: A plastic bottle, a pin or nail, sticky tape, water. Adult for making holes.

Do it: Make three holes one above the other. Cover them with tape, fill the bottle, then pull the tape off over a sink.

Why it works: Water spurts fastest from the bottom hole, because pressure in a liquid increases with depth. The jets also weaken as the water level falls.

34. Make a siphon

You need: Two containers, a length of clear plastic tube, water.

Do it: Put one container on a table and one on the floor. Fill the tube with water, hold both ends closed, put one end in the upper container and the other in the lower one, then release.

Why it works: Water flows up over the rim and down into the lower container. Gravity pulls the longer column of water down, and the water's cohesion and the surrounding air pressure keep the column unbroken behind it.

35. Pepper and soap

You need: A plate of water, ground pepper, washing-up liquid.

Do it: Sprinkle pepper over the water. Touch the surface in the middle with a soapy finger.

Why it works: The pepper rushes to the edges. Soap lowers the surface tension where it touches, and the stronger surface tension at the edges pulls the surface, and the pepper, outwards.

36. Floating paperclip

You need: A bowl of water, a paperclip, a small piece of tissue paper.

Do it: Lay the paperclip on the tissue and gently place both on the water. The tissue soaks and sinks, leaving the clip floating.

Why it works: Steel is about eight times denser than water, but surface tension supports the clip like a stretched skin. Add a drop of soap nearby and it sinks.

37. Drops on a coin

You need: A coin, a dropper or straw, water, soapy water.

Do it: Count how many drops of water you can add to the coin before it overflows. Repeat with soapy water.

Why it works: Plain water forms a tall dome held together by surface tension, so the coin holds far more drops than you would expect. Soapy water has lower surface tension, so it spills sooner.

38. Walking water

You need: Three glasses, paper towels, water, two food colourings.

Do it: Put coloured water in the outer glasses and leave the middle one empty. Fold paper towels into strips connecting each outer glass to the middle one. Wait an hour.

Why it works: Water climbs the paper by capillary action, drawn into the tiny gaps between fibres by attraction to the fibres and surface tension. The colours mix in the middle glass.

39. Cloud in a bottle

You need: A clear plastic bottle, a little warm water.

Do it: Swirl some warm water in the bottle and screw the cap on. Squeeze hard, then release quickly. Repeat a few times. A bicycle-pump bottle stopper gives a stronger effect.

Why it works: Releasing the squeeze lets the air expand and cool, which can make water vapour condense into a faint cloud. Real clouds form the same way as rising air expands and cools. Tiny particles help: an adult can drop in the smoke from a blown-out match.

40. Balloon on a bottle

You need: An empty plastic bottle, a balloon, a bowl of hot tap water and a bowl of iced water.

Do it: Stretch the balloon over the bottle's neck. Stand the bottle in hot water, then move it to the iced water.

Why it works: Warm air expands and partly inflates the balloon; cold air contracts and the balloon deflates or is sucked in. Pressure, volume and temperature are linked by the gas laws.

Heat and energy

These show conduction, convection, radiation and phase changes (OpenStax College Physics 2e, chapters 13–15).

41. Hot and cold water layers

You need: Two small identical bottles or jars, hot tap water with red food colouring, cold water with blue food colouring, a plastic card.

Do it: Fill both jars to the brim. Cover the cold jar with the card, turn it over and place it on top of the hot jar, then slide the card out. Over a tray, try it the other way round.

Why it works: With hot on the bottom, the colours mix quickly, because warm water is less dense and rises. With cold on the bottom, they stay separate for a long time. This is convection.

42. Which spoon conducts best?

You need: A metal spoon, a plastic spoon, a wooden spoon, butter, small beads, a mug of hot water. Adult for the hot water.

Do it: Stick a bead to the top of each handle with a dab of butter. Stand all three spoons in the hot water and watch.

Why it works: The bead on the metal spoon falls first, because metals conduct heat much better than plastic or wood. That is why pan handles are made of poor conductors.

43. Ice cube insulation challenge

You need: Identical ice cubes, materials such as foil, cotton wool, newspaper, wool fabric and bubble wrap, small cups.

Do it: Wrap each ice cube in a different material and leave one unwrapped. Check every 15 minutes and record which melts last.

Why it works: Good insulators trap still air, which conducts heat poorly, so heat reaches the ice more slowly. A wool jumper keeps ice cold for the same reason it keeps you warm.

44. Pizza-box solar oven

You need: A pizza box, foil, black paper, cling film, tape, a marshmallow or a piece of chocolate. A sunny day.

Do it: Cut a flap in the lid and line it with foil. Line the base with black paper, cover the opening with cling film, and angle the foil flap to reflect sunlight in.

Why it works: The foil reflects extra sunlight inside, the black paper absorbs it, and the cling film traps the warm air. On a hot, sunny day it can soften marshmallows, but do not expect it to cook raw food safely.

45. Black vs white in the sun

You need: Two identical glasses of water, black paper, white paper, a thermometer, sunshine.

Do it: Wrap one glass in each colour and leave both in the sun for an hour. Measure both temperatures.

Why it works: The black-wrapped water gets warmer. Dark surfaces absorb more visible light and white surfaces reflect more, which is why light-coloured roofs and clothes stay cooler.

46. Ice on metal vs plastic

You need: Two ice cubes, a metal baking tray or pan, a plastic chopping board.

Do it: First touch both surfaces: which feels colder? Then put an ice cube on each and watch which melts faster.

Why it works: The metal feels colder but melts the ice much faster. Both surfaces are at room temperature, but metal conducts heat quickly, into the ice or out of your hand. Your skin senses heat flow, not temperature.

47. Evaporation cooling

You need: Two thermometers, a damp cotton cloth or tissue, a fan if you have one.

Do it: Wrap one thermometer bulb in the damp cloth and leave the other dry. Fan both for a few minutes.

Why it works: The wet thermometer reads lower, because evaporating water takes latent heat from it. The drier the air, the bigger the difference, which is how weather stations measure humidity.

48. Lifting ice with string

You need: An ice cube, a piece of string, salt, a glass of water.

Do it: Float the ice cube in the water and lay the string across it. Sprinkle salt over the string, wait a minute, then lift.

Why it works: Salt lowers the freezing point, so ice under the salt melts. That melting draws heat from the surrounding water, which refreezes around the string and holds it.

49. Hot and cold rubber band

You need: A wide rubber band.

Do it: Hold it lightly against your lips or forehead. Stretch it quickly and feel it, then let it relax quickly and feel again.

Why it works: Stretching warms the band slightly, and relaxing cools it. Stretching lines up the long rubber molecules, and the work you do appears as heat. Your lips are sensitive enough to detect the small change.

50. Supercooled water

You need: Unopened bottles of purified or distilled water, a freezer, a timer.

Do it: Lie the bottles in the freezer for around two hours, checking often; the right time depends on your freezer. Carefully take out one that is still liquid and tap it hard or pour it onto an ice cube.

Why it works: Pure water can cool below 0 °C without freezing if nothing starts the ice crystals off. A knock or an ice crystal triggers rapid freezing. Results are unpredictable, so be patient.

51. Find the dew point

You need: A shiny metal can or tin, water, ice, a thermometer.

Do it: Fill the can with water and add ice a little at a time, stirring with the thermometer. Note the temperature at which the outside of the can mists over.

Why it works: That temperature is the dew point, where air touching the cold can is saturated and water vapour condenses. Humid days give a dew point close to the air temperature.

Waves and sound

These show vibration, pitch, resonance and how sound travels (OpenStax College Physics 2e, chapters 16–17).

52. Slinky waves

You need: A Slinky or long spring, a smooth floor, a partner.

Do it: Stretch it out between you. Shake one end side to side, then push and pull it along its length.

Why it works: Side-to-side shaking makes a transverse wave, like light. Pushing and pulling makes compressions travel along it, a longitudinal wave like sound. Watch the pulses reflect from your partner's end.

53. Water-glass xylophone

You need: Six identical glasses, water, a metal spoon.

Do it: Fill the glasses with different amounts of water and tap each one gently.

Why it works: Tapping makes the glass and water vibrate. More water adds mass and lowers the pitch. Blowing across the top of a bottle does the opposite: more water means a shorter air column and a higher note.

54. Straw pan pipes

You need: Drinking straws, scissors, tape.

Do it: Cut straws to different lengths, line them up from longest to shortest and tape them together. Blow across the tops.

Why it works: Each straw holds a vibrating column of air. Shorter columns resonate at higher frequencies, giving higher notes.

55. String telephone

You need: Two paper cups, a long piece of string, a pencil.

Do it: Make a hole in the base of each cup, thread the string through and knot it. Pull the string tight and talk into one cup while a partner listens.

Why it works: Your voice makes the cup base vibrate, the taut string carries the vibrations, and the other cup turns them back into sound. Let the string go slack and it stops working.

56. Spoon bells

You need: A metal spoon, a piece of string about 1 m long.

Do it: Tie the spoon to the middle of the string and press the string ends against your ears. Let the spoon swing and knock against a table.

Why it works: You hear a deep, bell-like sound. Vibrations travel along the string straight to your ears, and solids carry sound much better than air does.

57. Seeing sound

You need: A bowl, cling film, an elastic band, a pinch of salt or rice, a phone speaker.

Do it: Stretch cling film tightly over the bowl, sprinkle salt on top, and play a low note or speak loudly nearby.

Why it works: Sound waves make the film vibrate, and the salt jumps and collects in patterns at points that vibrate least. Different notes make different patterns.

58. Doppler effect from the roadside

You need: A phone with a voice recorder, a safe spot on a pavement beside a road where cars pass at a steady speed.

Do it: Record the sound of cars approaching and passing. Play it back and listen to the pitch.

Why it works: The engine and tyre noise drops in pitch as each car passes you. Sound waves bunch up in front of a moving source and spread out behind it. Free spectrum-analyser apps show the frequency drop as a line on a graph.

59. Speed of sound from an echo

You need: A large flat wall with open space in front of it, a tape measure or map, a stopwatch, a partner.

Do it: Stand at least 50 m from the wall and clap. Then clap in rhythm so each clap coincides with the echo of the previous one. Your partner times 20 claps.

Why it works: Each interval between claps is the time sound takes to travel to the wall and back. Speed equals twice the distance divided by that time. You should get a value near 340 m/s.

60. Singing glass

You need: A thin wine glass, water. Adult if the glass is delicate.

Do it: Hold the base firmly, wet your finger and run it slowly round the rim. Add water and repeat.

Why it works: Your finger alternately sticks and slips, making the glass vibrate at its natural frequency until it rings. Adding water lowers the pitch, because it adds mass to the vibrating walls.

61. Ruler twang

You need: A plastic or wooden ruler, a table.

Do it: Hold one end firmly on the table with the rest sticking out over the edge. Twang the free end, then change how far it sticks out.

Why it works: A shorter overhang vibrates faster and makes a higher note. A longer one vibrates slowly enough for you to see each swing.

62. Ripple tank in a baking dish

You need: A glass baking dish, water, a phone torch, white paper, a pencil.

Do it: Put the dish on the paper with about 1 cm of water. Shine the torch from above and tap the water with a pencil. Then tap two points at once, or put a gap in a barrier made from a ruler.

Why it works: The ripples act like lenses and cast bright and dark lines on the paper. You can see waves reflecting, spreading through a gap (diffraction) and overlapping (interference).

Light and colour

These show reflection, refraction, dispersion and polarisation (OpenStax College Physics 2e, chapters 25–27).

63. Bent pencil

You need: A glass of water, a pencil.

Do it: Stand the pencil in the glass and look from the side.

Why it works: The pencil seems broken at the water's surface. Light from the underwater part bends as it leaves the water, so it appears to come from a different place.

64. Disappearing coin

You need: A coin, a glass, water.

Do it: Put the glass on top of the coin and look through the side of the glass. Fill the glass with water and look again from the side.

Why it works: With water in the glass, the coin vanishes when viewed through the side. Light from the coin travels steeply upwards through the water and meets the side wall at too shallow an angle to escape, so it is totally internally reflected instead of reaching your eye. Look down from the top and the coin is still there.

65. Arrow reversal

You need: A clear glass, water, a piece of paper with an arrow drawn on it.

Do it: Stand the paper behind the empty glass, then fill the glass and look through it. Move the paper closer and further away.

Why it works: The water-filled glass acts as a cylindrical lens. Beyond a certain distance, light rays cross over inside it, so the arrow appears to point the other way.

66. Water-drop magnifier

You need: Cling film or a clear plastic sheet, a dropper, water, some printed text.

Do it: Lay the plastic over the text and put a single drop of water on it.

Why it works: The curved drop is a tiny convex lens and magnifies the letters. Smaller, rounder drops are more curved and magnify more.

67. Pinhole camera

You need: A cardboard tube or box, foil, a pin, greaseproof or tracing paper, tape.

Do it: Cover one end with foil and make a pinhole in the centre. Cover the other end with the tracing paper. Point the pinhole at a bright window and look at the paper with a cloth over your head.

Why it works: Light travels in straight lines, so rays from the top of the scene pass through the hole and land at the bottom of the screen. You see an upside-down image. A bigger hole is brighter but blurrier.

68. Make a rainbow

You need: A glass of water, a sunny windowsill, white paper. Or a garden hose on a sunny day.

Do it: Put the glass on the edge of the sunny windowsill and the paper on the floor below. Move the paper until a spectrum appears. Outside, spray a fine mist with your back to the Sun.

Why it works: Water refracts each colour by a slightly different amount, separating white light into a spectrum. This is dispersion, the same process that makes real rainbows.

69. CD spectroscope

You need: An old CD or DVD, a cardboard tube or box, foil, tape.

Do it: Make a narrow slit at one end of the box with foil, and fix the CD at an angle at the other end with a viewing hole above it. Point the slit at different light sources (not the Sun).

Why it works: The closely spaced tracks of the disc act as a diffraction grating and split light into its colours. Sunlight reflected off a white wall gives a continuous spectrum; some fluorescent and LED lights show separate bright bands.

70. Light trapped in water

You need: A clear plastic bottle, water, a small laser pointer (low power, Class 2) or a bright narrow torch, a sink. Adult supervision.

Do it: Make a hole near the bottom of the bottle and fill it with water. In a dark room, shine the laser through the bottle from the far side so it lines up with the hole, and let the water stream out into the sink.

Why it works: The light follows the curved stream, because it keeps hitting the water's surface at a shallow angle and reflects back in. This total internal reflection is how optical fibres carry data.

71. Infinity mirror

You need: Two mirrors, or a mirror and a phone screen in selfie mode.

Do it: Hold two mirrors facing each other, nearly parallel, and look over the edge of one.

Why it works: Light bounces back and forth between the mirrors, making a line of images that fades into the distance. Each reflection loses a little light, which is why the far images are dimmer and slightly greenish: mirror glass absorbs some colours a little more than others.

72. Milk-carton periscope

You need: Two juice or milk cartons, two small mirrors, scissors, tape. Adult for cutting.

Do it: Join the cartons into one tall tube. Cut a window near the top on one side and near the bottom on the opposite side. Fix a mirror at 45° behind each window, facing each other.

Why it works: Light enters the top window, reflects down off the first mirror, then reflects off the second mirror into your eye. Each reflection follows the law that the angle in equals the angle out.

73. Two pairs of polarised sunglasses

You need: Two pairs of polarised sunglasses, or one pair and a laptop or phone screen.

Do it: Look through one lens at the other, and rotate one pair slowly. Or look at an LCD screen through one lens and tilt your head.

Why it works: At one angle the overlapping lenses go dark. Each lens only passes light vibrating in one direction, so when they are at right angles, almost nothing gets through. Many LCD screens already give out polarised light. (Some phone screens are designed to look the same at all angles.)

74. Rainbow stress patterns

You need: Clear plastic objects such as a ruler, a CD case or plastic cutlery, a white laptop or tablet screen, a pair of polarised sunglasses.

Do it: Hold the plastic in front of the white screen and look at it through the sunglasses. Bend the plastic slightly.

Why it works: Coloured bands appear where the plastic is stressed. Stress changes how the plastic affects polarised light, differently for each colour. Engineers use this effect, photoelasticity, to see stress in models of structures.

75. Why the sky is blue

You need: A clear glass of water, a few drops of milk, a torch, a dark room.

Do it: Stir the milk into the water. Shine the torch through the side and look from the side, then look through the glass straight at the torch.

Why it works: From the side the water looks faintly blue; looking through it towards the torch, the light looks orange. Tiny particles scatter blue light more than red. The atmosphere does the same with sunlight, which is why the sky is blue and sunsets are red. (The particles in milk are larger than air molecules, so the effect here is weaker than in the sky.)

76. See the pixels in a screen

You need: A phone or tablet, a drop of water or a magnifying glass.

Do it: Display a white image and look closely through the magnifier, or place a single tiny drop of water on the screen (wipe it off afterwards).

Why it works: The white is made of tiny red, green and blue sub-pixels. Your eye blends them, because colour vision relies on three types of cone cells that respond most to red, green and blue light.

77. Spinning picture (thaumatrope)

You need: A card disc, a pencil, string or a straw, tape.

Do it: Draw a bird on one side and an empty cage on the other, upside down relative to the first. Tape the disc to a straw and spin it between your palms.

Why it works: The bird appears inside the cage. Your visual system blends images that alternate quickly. This is about perception rather than pure physics, but it is the basis of film and animation frame rates.

78. Measure a tree with a shadow

You need: A sunny day, a tape measure, a stick of known length.

Do it: Stand the stick upright and measure its shadow. At the same time, measure the shadow of a tree or building.

Why it works: Sunlight arrives in effectively parallel rays, so the stick and the tree make similar triangles. The tree's height equals its shadow length times the stick's height divided by the stick's shadow length.

79. Speed of light with chocolate and a microwave

You need: A microwave oven, a large flat bar of chocolate or a plate of mini marshmallows, a ruler. Adult only.

Do it: Remove the turntable so the food does not rotate, and put the chocolate on an upside-down microwave-safe plate. Heat it in short bursts of about 15–20 seconds until a few melted spots appear. Measure the distance between neighbouring spots.

Why it works: Microwaves form standing waves in the oven, and the hot spots are about half a wavelength apart. The operating frequency is printed on the oven's label, usually 2,450 MHz. Speed of light $= 2 \times \text{spot spacing} \times \text{frequency}$. Spots 6.1 cm apart give about $3.0 \times 10^8$ m/s. Never run a microwave empty, and remove anything metallic.

80. Counting images in angled mirrors

You need: Two small mirrors, tape, a protractor, a small toy.

Do it: Tape the mirrors together along one edge like a book. Put the toy between them and count the images at 90°, 60° and 45°.

Why it works: Light reflects back and forth between the mirrors. For angles that divide 360° evenly, the number of images is $360°/\theta - 1$: 3 images at 90°, 5 at 60° and 7 at 45°. Kaleidoscopes work this way.

Electricity and magnetism

These show static charge, circuits, electromagnets and induction (OpenStax College Physics 2e, chapters 18–23). Use only AA or AAA batteries.

81. Bending water with a balloon

You need: A balloon, your hair or a wool jumper, a tap.

Do it: Run a thin, steady stream of water from the tap. Rub the balloon on your hair and bring it close to the stream without touching.

Why it works: The stream bends towards the balloon. The charged balloon attracts the opposite charge in the water. Water molecules are polar, with slightly positive and negative ends, so they are easily pulled by an electric field. It works best on dry days.

82. Jar electroscope

You need: A glass jar, a piece of card, a metal paperclip, kitchen foil, a balloon.

Do it: Push the paperclip through the card so it hangs inside the jar. Hang two small strips of foil from the bottom of the clip, and put a foil ball on the top. Bring a charged balloon near the ball.

Why it works: The foil strips spread apart. Charge moves through the metal, both strips end up with the same type of charge, and like charges repel.

83. Separate salt and pepper

You need: Salt, ground pepper, a plastic spoon, a wool cloth.

Do it: Mix a little salt and pepper on a plate. Rub the spoon with the cloth and hold it a few centimetres above the mixture.

Why it works: The pepper jumps up to the spoon first, because it is lighter. Bring the spoon lower and the salt follows too.

84. Lemon battery

You need: Three or four lemons, galvanised (zinc-coated) nails, copper coins or copper wire, crocodile-clip leads, a small red LED.

Do it: Push one nail and one copper piece into each lemon, not touching. Connect the lemons in series, copper of one to zinc of the next, then connect the LED to the free ends. Try both ways round, because LEDs only work in one direction.

Why it works: The two metals and the acidic juice form an electrochemical cell, giving roughly 0.9 V each. Several in series can light an LED dimly. The energy comes from the zinc reacting, not from the lemon itself; potatoes work too.

85. A simple circuit

You need: A two-AA battery holder, a small torch bulb in a holder, three wires or strips of foil, a paperclip as a switch.

Do it: Connect battery, switch and bulb in a loop. Then add a second bulb in series, and try two bulbs in parallel.

Why it works: Current only flows around a complete loop. Two bulbs in series share the voltage and glow dimmer; in parallel each gets the full voltage and glows brightly, but the battery runs down faster.

86. Conductor or insulator?

You need: The circuit from experiment 85 with a gap in it, household items such as a coin, a key, a pencil lead, a rubber band, a plastic spoon, kitchen foil.

Do it: Bridge the gap with each item and see whether the bulb lights.

Why it works: Metals conduct, so the bulb lights. Plastic, rubber and wood are insulators. Pencil "lead" is graphite, a form of carbon that conducts, so a pencil line may make the bulb glow faintly.

87. Squishy circuits

You need: Salt dough (flour, water, plenty of salt), sugar dough (flour, sugar, distilled or deionised water, oil), a battery pack, an LED.

Do it: Make two separate lumps of salt dough with a strip of sugar dough between them. Push the LED legs into the two salt lumps and connect the battery leads.

Why it works: Dissolved salt makes the dough a conductor, because the salt splits into charged ions that can move. Sugar dough has no ions, so it insulates. The LED lights only when current flows through it.

88. Make an electromagnet

You need: A large iron or steel nail, about 1 m of thin insulated copper wire, an AA battery, paperclips.

Do it: Wrap the wire tightly around the nail, leaving the ends free. Strip the ends and touch them to the battery terminals. Count how many paperclips the nail picks up. Try 20 turns, then 40.

Why it works: Current in the coil creates a magnetic field, and the iron core concentrates it. More turns or more current gives a stronger magnet. Connect only briefly: the wire and battery get warm.

89. Homopolar motor

You need: An AA battery, a small neodymium disc magnet, bare copper wire. Adult for the magnet.

Do it: Stand the battery on the magnet. Bend the wire so it touches the top terminal and loosely touches the side of the magnet at the bottom.

Why it works: Current flows down the wire and through the magnet's magnetic field, and the magnetic force on the moving charges spins the wire. This is the motor effect. It short-circuits the battery, so it gets hot quickly: run it for a few seconds only.

90. Floating needle compass

You need: A sewing needle, a strong magnet, a small slice of cork, a bowl of water.

Do it: Stroke the needle about 30 times in one direction with one end of the magnet. Push it through the cork and float it.

Why it works: Stroking lines up tiny magnetic regions in the steel, magnetising the needle. Floating lets it turn freely, and it lines up with Earth's magnetic field, pointing roughly north-south. Keep it away from metal objects.

91. Magnetic field patterns

You need: A magnet, a sheet of paper, iron filings or finely cut steel wool. Adult for cutting steel wool; wear gloves.

Do it: Put the paper over the magnet and sprinkle the filings on top. Tap the paper gently.

Why it works: Each filing becomes a tiny magnet and lines up along the field, showing the field lines running from pole to pole. Try two magnets with like and unlike poles facing.

92. Slow-falling magnet

You need: A copper pipe about 30 cm or longer (from a hardware shop), a strong neodymium magnet, a similar-sized non-magnetic object such as a steel nut. Adult for the magnet.

Do it: Drop the nut through the pipe, then drop the magnet.

Why it works: The magnet falls far more slowly. Its moving field induces swirling eddy currents in the copper, and by Lenz's law those currents create a magnetic field that opposes its fall. Copper is not magnetic; the effect comes from induction.

93. Shake-a-magnet generator

You need: A cardboard tube or plastic bottle, at least 200 turns of thin enamelled copper wire, a strong magnet that slides inside the tube, a multimeter set to millivolts. Adult for the magnet.

Do it: Wind the wire around the middle of the tube, sand the enamel off the ends and connect them to the multimeter. Shake the magnet back and forth through the coil.

Why it works: The changing magnetic field through the coil induces a voltage, which the meter shows flicking back and forth. Faster shaking and more turns give a bigger voltage. Power stations work on this principle.

94. How strength changes with distance

You need: A fridge magnet or bar magnet, a paperclip, a stack of playing cards or sheets of paper.

Do it: Put the magnet under one card and see whether it holds the paperclip on top. Keep adding cards until it falls off.

Why it works: The magnetic force falls off rapidly as distance increases, much faster than in proportion to distance. Plot cards against whether the clip holds, and compare different magnets.

95. Faraday cage

You need: A mobile phone, kitchen foil or a metal biscuit tin with a lid, a second phone.

Do it: Wrap the phone completely in several layers of foil, or seal it in the tin, and call it.

Why it works: The call often fails or the phone loses signal. A closed metal shell blocks radio waves, because they drive currents in the metal that cancel the field inside. Gaps or a poorly fitting lid let the signal through.

Earth, space and smartphone physics

These use your surroundings and a phone's built-in sensors. The free phyphox app, developed at RWTH Aachen University, can read a phone's accelerometer, gyroscope, magnetometer, barometer and microphone.

96. Measure acceleration in a lift

You need: A smartphone with an accelerometer app such as phyphox.

Do it: Lay the phone flat on the lift floor, start recording and ride up and down a few floors.

Why it works: The reading is about 9.8 m/s² at rest, rises as the lift starts upwards and dips as it slows. You are measuring the normal force changing, which is why you feel heavier and lighter.

97. Measure gravity with a pendulum

You need: String, a small heavy weight, a tape measure, a stopwatch.

Do it: Make a pendulum at least 1 m long. Measure the length from the pivot to the centre of the weight, then time 20 small swings.

Why it works: For small swings, $g = 4\pi^2 L/T^2$, where $T$ is the time for one swing out and back. A 1.00 m pendulum should have a period of about 2.0 s, giving a value close to 9.8 m/s².

98. Toilet-paper solar system

You need: A roll of toilet paper, markers, a long corridor or garden.

Do it: Let one sheet equal 10 million km. Mark the Sun at the start, then the planets at the right number of sheets: about 6 for Mercury, 15 for Earth, 78 for Jupiter and about 450 for Neptune.

Why it works: The inner planets crowd together, and the outer planets are enormously far away. Real distances are at NASA's planetary fact sheet.

99. Moon phases with a lamp

You need: A lamp without a shade, a ball on a stick or a pencil pushed into a polystyrene ball, a dark room. Adult for the hot bulb.

Do it: Stand facing the lamp with the ball held at arm's length, slightly above your head. Turn slowly in a circle and watch the lit part of the ball.

Why it works: You see the ball go from new to crescent, half, gibbous and full. Half the Moon is always lit by the Sun; phases are how much of that lit half we can see from Earth.

100. Crater formation

You need: A tray of flour, cocoa powder, marbles or stones of different sizes, a ruler.

Do it: Smooth the flour and dust cocoa over the top. Drop marbles from different heights and measure each crater's width.

Why it works: Higher drops give the marble more kinetic energy, which makes wider craters and longer "rays" of thrown-out flour. Craters on the Moon form in a similar way, though real impacts are far faster.

101. Measure the Sun's diameter safely

You need: Two pieces of card, a pin, a tape measure, a sunny day. Never look at the Sun.

Do it: Make a pinhole in one card. With your back to the Sun, hold the second card in its shadow, about 1–2 m away, and measure the diameter of the bright disc and the distance between the cards.

Why it works: The Sun's image, the pinhole and the Sun itself form similar triangles. Sun's diameter = image diameter × Sun's distance ÷ card distance. Using an Earth-Sun distance of about 150 million km, a 1 cm image at 107 cm gives about 1.4 million km, close to the measured value.

Where to go next

• Understand the ideas behind these experiments in 100 physics concepts explained with real-world examples.
• Do the calculations for experiments 5, 15, 59, 79 and 97 with 100 physics formulas every student should know.
• Turn a demonstration into a full investigation with 101 physics projects for students.
• See the same physics at work in 100 applications of physics in everyday life.
• Browse more articles and blogs in the physics category.

References

• College Physics 2e, Paul Peter Urone and Roger Hinrichs, OpenStax (2022). https://openstax.org/details/books/college-physics-2e
• University Physics Volume 1, William Moebs, Samuel J. Ling and Jeff Sanny, OpenStax (2016). https://openstax.org/details/books/university-physics-volume-1
• "Science Snacks", Exploratorium (hands-on activities using common materials). https://www.exploratorium.edu/snacks
• "Practical Physics", Institute of Physics (teacher-tested classroom experiments). https://spark.iop.org/practical-physics
• phyphox, RWTH Aachen University (free app for smartphone sensor experiments). https://phyphox.org/
• "Planetary Fact Sheet", NASA Space Science Data Coordinated Archive. https://nssdc.gsfc.nasa.gov/planetary/factsheet/
• "Fundamental Physical Constants: 2022 CODATA values", NIST Physical Measurement Laboratory. https://physics.nist.gov/cuu/Constants/