Science

100 Best Applications of Science in Everyday Life: A Complete Guide

How chemistry, biology and Earth science shape 100 everyday things, from bread, soap and vaccines to clean water, fertilisers, glue and weather forecasts.

By BlogAI Editors · · 25 min read

Before breakfast, you have probably used dozens of scientific discoveries without noticing. The fluoride in your toothpaste, the yeast in your bread, the chlorine that made your tap water safe and the enzymes in your laundry detergent all come from chemistry and biology worked out over the last two centuries.

This guide explains 100 applications of science in everyday life, grouped by where you meet them: the kitchen, cleaning, health and medicine, personal care, materials around the home, farming, water and the environment, transport and energy, and public safety. For each one, you will find what it does and the science that makes it work.

What this guide covers. It focuses on chemistry, biology and Earth science. Devices that run mainly on physics, such as microwaves, touchscreens, GPS, MRI scanners and solar panels, are explained in our companion guide, 100 applications of physics in everyday life, so they are not repeated here. Explanations follow the OpenStax textbooks and the public health, food safety and environmental agencies linked in each section (see References). This is general information, not medical advice.

In the kitchen

Cooking is applied chemistry and microbiology (OpenStax Chemistry 2e; OpenStax Microbiology).

1. Bread rising

Yeast is a living fungus. Mixed into dough, it ferments sugars and releases carbon dioxide, which is trapped by a stretchy network of gluten proteins, so the dough rises. Baking kills the yeast, evaporates the small amount of alcohol produced and sets the structure.

2. Baking powder and baking soda

Cakes and scones rise thanks to carbon dioxide from a chemical reaction rather than yeast. Baking soda reacts with acidic ingredients such as buttermilk or yoghurt. Baking powder contains its own dry acid, and "double-acting" powders release some gas when mixed and more when heated in the oven.

3. Browning and flavour

The crust on bread, the colour of roasted coffee and the flavour of a seared steak come from the Maillard reaction between amino acids and sugars at high temperature. Caramelisation of sugars adds more colour and flavour. Cooks control both by adjusting temperature, moisture and time.

4. Pasteurisation

Heating milk and juices to a set temperature for a set time, commonly 72 °C for 15 seconds for milk, kills disease-causing microbes while changing the flavour very little. Louis Pasteur developed the idea for wine and beer in the 1860s. It has made milk one of the safest foods.

5. Canning

Sealed cans and jars are heated to kill microbes and their spores, and the seal stops new ones getting in. Low-acid foods such as vegetables and meat must be heated under pressure to well above boiling point to destroy the spores of Clostridium botulinum, which can cause deadly botulism (USDA).

6. Preserving with salt, sugar and drying

Salt-cured fish, jam, honey and dried fruit last a long time because microbes need water to grow. High concentrations of salt or sugar pull water out of microbial cells by osmosis, and drying removes the water altogether. This is some of the oldest applied science in the world.

7. Fermented foods

Yoghurt, cheese, sauerkraut, kimchi, soy sauce and sourdough are made by harmless microbes that turn sugars into acids, gases or alcohol. The acid both preserves the food and creates its characteristic taste and texture. Food scientists now choose specific starter cultures to make fermentation reliable.

8. Cheese-making enzymes

Cheese starts when the enzyme chymosin makes milk proteins clump into curds. It traditionally came from calves' stomachs (rennet), but much of the chymosin used today is made by genetically engineered microbes, an early everyday use of biotechnology.

9. Lactose-free milk

Many adults produce little lactase, the enzyme that digests milk sugar. Lactose-free milk has lactase added during processing, which splits lactose into glucose and galactose. The milk tastes slightly sweeter because those sugars taste sweeter than lactose.

10. Jam setting

Jam sets because pectin, a natural carbohydrate in fruit cell walls, forms a gel network when there is enough sugar and acid. That is why jam recipes often add lemon juice, and why low-pectin fruits such as strawberries may need extra pectin.

11. Meat tenderisers and marinades

Meat-tenderising powders contain protein-digesting enzymes from papaya (papain) or pineapple (bromelain) that break down tough connective tissue. Acidic marinades with vinegar, wine or citrus also loosen proteins at the surface, although they penetrate only a short way into the meat.

12. Emulsions: mayonnaise and sauces

Oil and water do not normally mix. Emulsifiers have one part that is attracted to water and another to oil, so they coat tiny oil droplets and stop them joining together. Egg yolk lecithin holds mayonnaise together; manufacturers also use emulsifiers in chocolate, ice cream and salad dressings.

13. Decaffeinated coffee

Caffeine can be removed from green coffee beans by soaking them in water and filtering it out with activated carbon, by using solvents, or with supercritical carbon dioxide: carbon dioxide under such high pressure that it behaves partly like a liquid and dissolves caffeine selectively.

14. Packaging that keeps food fresh

Bagged salads and meats are often sealed in a modified atmosphere with less oxygen and more nitrogen or carbon dioxide, which slows the growth of microbes and browning. Small sachets in some packets contain iron powder, which absorbs oxygen as it rusts.

15. Food fortification

Adding nutrients to everyday foods has prevented whole diseases. Iodised salt prevents iodine deficiency, which can cause goitre and harm brain development. Adding folic acid to flour in many countries has reduced the number of babies born with neural tube defects such as spina bifida (CDC).

16. Artificial sweeteners

Sweeteners such as aspartame, sucralose and stevia extracts bind to the tongue's sweet-taste receptors far more strongly than sugar, so a tiny amount gives the same sweetness with almost no calories. Each one is assessed for safety by food regulators before it can be used.

Cleaning

Most cleaning products work by dissolving, lifting or breaking down dirt using chemistry (OpenStax Chemistry 2e).

17. Soap

Soap molecules have a water-loving head and an oil-loving tail. The tails bury themselves in grease, and the heads face the water, so oily dirt is wrapped in tiny balls called micelles and rinsed away. This is also how soap destroys many viruses: it breaks apart their fatty outer envelope.

18. Laundry detergents and enzymes

Modern detergents contain synthetic surfactants that work even in hard water, plus enzymes that digest specific stains: proteases for blood and egg, amylases for starch, and lipases for grease. Because enzymes work at moderate temperatures, they let clothes be washed effectively at 30 or 40 °C, saving energy.

19. Bleach

Household chlorine bleach contains sodium hypochlorite, which oxidises coloured stain molecules and kills microbes by damaging their proteins. Never mix bleach with acids, such as vinegar or some toilet cleaners, or with ammonia: these combinations release toxic gases.

20. Descaling with vinegar

The white crust in kettles and showerheads is limescale, mostly calcium carbonate left behind when hard water is heated or evaporates. Acids such as vinegar or citric acid react with it and dissolve it, releasing carbon dioxide bubbles.

21. Hand sanitiser

Alcohol-based hand sanitisers kill many bacteria and viruses by disrupting their proteins and membranes. The US Centers for Disease Control and Prevention recommends products with at least 60 percent alcohol, and notes that soap and water work better when hands are visibly dirty or greasy (CDC).

22. Disinfectants

Disinfectants such as bleach, hydrogen peroxide and quaternary ammonium compounds kill microbes on surfaces, but only if left wet on the surface for the "contact time" on the label. Cleaning first removes dirt that can shield germs.

23. Dishwasher detergent

Dishwasher tablets are strongly alkaline to break down fats and proteins, and contain enzymes, bleaching agents and chemicals that bind calcium and magnesium. Rinse aid contains surfactants that make water sheet off dishes instead of forming droplets that leave spots.

24. Water softeners

Home water softeners pass hard water through beads of ion-exchange resin, which swap calcium and magnesium ions for sodium ions. The water then lathers better and leaves less scale. The resin is regularly recharged by flushing it with strong salt solution.

25. Fluoride toothpaste

Fluoride helps tooth enamel repair itself and forms fluorapatite, a mineral more resistant to acid than natural enamel. Bacteria in plaque produce acid from sugars, so fluoride helps prevent tooth decay. Many communities also add small amounts of fluoride to drinking water (CDC).

Health and medicine

Medicine depends on chemistry and biology at every step. Imaging technologies such as X-rays and MRI are covered in our physics applications guide (OpenStax Microbiology).

26. Vaccines

Vaccines train the immune system by showing it a harmless version or part of a germ, so it builds memory cells that respond quickly to the real infection (CDC). Vaccination eradicated smallpox and has made diseases such as measles, polio and diphtheria rare in many countries.

27. mRNA vaccines

Instead of delivering part of a germ, mRNA vaccines deliver genetic instructions that tell your cells to make a harmless piece of it, such as the spike protein of the virus that causes COVID-19. The mRNA is broken down within days. The technology let new vaccines be designed and manufactured unusually fast.

28. Antibiotics

Antibiotics kill bacteria or stop them multiplying by attacking structures that human cells do not have, such as bacterial cell walls and ribosomes. They do not work against viruses. Using them only when needed slows the spread of antibiotic resistance (CDC).

29. Painkillers

Aspirin and ibuprofen block enzymes called cyclooxygenases, which make chemical signals involved in pain, fever and inflammation. Aspirin's history goes back to willow bark, which contains a related compound, salicin; chemists at Bayer made a version easier on the stomach in 1897.

30. Oral rehydration solution

A simple mix of water, salt and sugar in the right proportions saves lives from diarrhoea. The gut absorbs sodium and glucose together, and water follows by osmosis, so the solution replaces lost fluid even when the gut is inflamed. The World Health Organization and UNICEF promote it worldwide.

31. Insulin from engineered microbes

People with type 1 diabetes once relied on insulin extracted from pig and cow pancreases. Since 1982, human insulin has been made by bacteria or yeast that carry the human insulin gene, one of the first medicines produced by genetic engineering.

32. Blood transfusions

Transfusions are safe because blood is matched by group. Red cells carry A, B or neither antigen, and the Rh factor, while plasma contains antibodies that attack the wrong type. Blood banks test and match every unit to avoid a dangerous reaction.

33. Anaesthesia

General anaesthetics are drugs that make patients unconscious and unaware of pain during surgery, while anaesthetists monitor breathing, heart rate and blood pressure. Local anaesthetics, used by dentists, block nerve signals from one area by stopping sodium ions from entering nerve cells.

34. Sterilising medical equipment

Hospitals sterilise surgical instruments in autoclaves, which use steam under pressure, typically at 121 °C or higher, to kill even heat-resistant bacterial spores. Single-use items are often sterilised with gamma radiation or ethylene oxide gas.

35. Pregnancy and rapid tests

Lateral-flow tests, used for pregnancy, COVID-19 and some other infections, contain antibodies that bind a specific target molecule, such as the pregnancy hormone hCG. The bound target is carried along a strip and caught by a second line of antibodies attached to coloured particles, producing a visible line.

36. PCR tests

The polymerase chain reaction copies a specific stretch of DNA over and over, doubling it each cycle, until there is enough to detect. It can find the genetic material of a virus or bacterium in a tiny sample and is used for diagnosis, forensics and genetic testing.

37. Blood glucose meters

A finger-prick glucose meter uses an enzyme on a test strip to react with glucose in the blood. The reaction produces a tiny electric current proportional to the glucose concentration, which the meter converts into a reading. Continuous monitors use a similar sensor under the skin.

38. Statins and heart disease

Statins lower cholesterol by blocking an enzyme the liver uses to make it, called HMG-CoA reductase. Lower levels of LDL cholesterol in the blood reduce the build-up of fatty plaques in arteries and the risk of heart attacks and strokes in people at high risk.

39. Targeted cancer drugs

Some cancer medicines attack a specific molecule that drives a particular cancer. Imatinib, approved in 2001, blocks the faulty protein that causes chronic myeloid leukaemia and transformed the outlook for many patients. Doctors test tumours' DNA to choose such treatments.

40. Allergy medicines

During an allergic reaction, immune cells release histamine, which causes itching, sneezing and swelling. Antihistamines block histamine receptors so the signal cannot take effect. Newer antihistamines cross into the brain less, which is why they cause less drowsiness.

41. Genetic testing

Reading a person's DNA can confirm a diagnosis of an inherited disease, guide the choice or dose of some medicines, and screen newborns for treatable conditions. Newborn blood-spot screening for disorders such as phenylketonuria lets diet or treatment start before damage occurs.

42. Clinical trials

Before a medicine is approved, it is tested in clinical trials. In a randomised controlled trial, patients are assigned by chance to the new treatment or a comparison, often without knowing which they received. This design is the scientific method applied to medicine, and it separates real effects from chance and expectation.

43. Monitoring disease in wastewater

Health agencies test sewage for genetic material from viruses such as SARS-CoV-2, poliovirus and influenza. Because almost everyone uses the toilet, wastewater gives an early, anonymous picture of what is spreading in a community (CDC).

Personal care

Bathroom shelves are full of chemistry (OpenStax Chemistry 2e).

44. Shampoo and conditioner

Shampoos use surfactants, like soap, to lift oil and dirt from hair. Hair surfaces carry a slight negative charge, especially when damaged, so conditioners contain positively charged molecules that stick to the hair, smoothing it and reducing static.

45. Permanent hair dye

Permanent dyes mix an alkaline cream, often containing ammonia, with hydrogen peroxide. The alkali swells the hair's outer layer so small dye precursor molecules can get inside. The peroxide lightens natural pigment and links the precursors into large coloured molecules that are trapped in the hair.

46. Antiperspirants and deodorants

Body odour comes from bacteria breaking down sweat, not from sweat itself. Deodorants contain antimicrobials and fragrance. Antiperspirants also contain aluminium salts that form temporary plugs in sweat ducts, reducing how much sweat reaches the skin.

47. Sunscreen

Sunscreens use UV filters. Chemical filters absorb ultraviolet light and release the energy as a tiny amount of heat; mineral filters such as zinc oxide and titanium dioxide absorb and scatter it. SPF measures protection against UVB, which causes sunburn, and "broad spectrum" means it also protects against UVA (FDA).

48. Nail polish and remover

Nail polish is a polymer dissolved in fast-evaporating solvents, with pigments added. When the solvent evaporates, the polymer forms a hard film. Remover, usually acetone or ethyl acetate, dissolves the film again.

49. Moisturisers

Moisturisers combine humectants, such as glycerin, that attract water into the skin; emollients that smooth rough skin; and occlusives, such as petroleum jelly, that form a barrier to slow water loss. Most creams are emulsions of oil and water held together by emulsifiers.

50. Food labels and calories

The calories on food labels are calculated mostly from standard energy values for each nutrient, about 4 kilocalories per gram for protein and carbohydrate and 9 for fat. These factors were originally derived from burning foods in a calorimeter and measuring what the body could absorb.

Materials around the home

Everyday materials are designed at the level of molecules (OpenStax Chemistry 2e, chapter 20).

51. Plastics

Plastics are polymers: very long molecules made by linking thousands of small units. The structure of the chain decides the properties. Polyethylene is soft and flexible for bags and bottles, polypropylene withstands heat for food tubs, and PET is clear and strong for drinks bottles.

52. Recycling codes

The number inside the recycling triangle on plastic items identifies the type of polymer, from 1 (PET) to 7 (other). It tells recyclers what the plastic is, but it does not mean the item is recyclable where you live. Different polymers must be separated because they melt and behave differently.

53. Non-stick pans

Non-stick coatings are made of PTFE, a polymer of carbon and fluorine whose surface almost nothing sticks to. PFOA, a chemical once used to manufacture PTFE, has been phased out in many countries because of health and environmental concerns (US EPA). Overheating an empty pan can damage the coating.

54. Superglue

Superglue is a liquid made of cyanoacrylate molecules. Traces of water on almost any surface, including the moisture in the air, trigger the molecules to link rapidly into long polymer chains, setting the glue in seconds. That is why it also sticks skin so quickly.

55. Paint

Paint is a pigment for colour, a binder that forms a film, and a liquid that evaporates. In water-based emulsion paint, tiny particles of polymer fuse together as the water evaporates. Oil-based paints harden as their oils react with oxygen from the air.

56. Concrete

Concrete hardens through a chemical reaction, not by drying. Cement reacts with water to form interlocking crystals that bind sand and gravel together. That is why concrete is kept damp while it cures, and why it keeps gaining strength for weeks.

57. Stainless steel

Steel with at least 10.5 percent chromium forms an invisible, self-repairing layer of chromium oxide on its surface. This layer stops oxygen and water reaching the iron underneath, so cutlery and sinks stay rust-free.

58. Galvanised steel

Buckets, fences and car bodies are often coated in zinc. Zinc is more reactive than iron, so if the coating is scratched, the zinc corrodes instead of the steel. This "sacrificial" protection is also used to protect ships and pipelines.

59. Glass and heat-resistant glass

Ordinary window and bottle glass is made by melting sand (silica) with soda and lime. Heat-resistant borosilicate glass adds boron oxide, which makes it expand much less when heated, so it is less likely to crack from sudden temperature changes.

60. Household batteries

An alkaline battery separates a reaction between zinc and manganese dioxide so that electrons can flow only through your device. Car batteries use lead and sulphuric acid and can be recharged by reversing the reaction. Lithium-ion batteries are covered in our physics applications guide.

61. Fire extinguishers

Extinguishers break the fire triangle of fuel, heat and oxygen. Water cools burning wood and paper, foam smothers flammable liquids, carbon dioxide displaces oxygen and is safe on electrical equipment, and dry powder interrupts the chemical reactions in the flame. Using the wrong type, such as water on an oil fire, can make a fire worse.

62. The smell of gas

Natural gas has no smell, so suppliers add tiny amounts of sulphur compounds called mercaptans, which humans can smell at extremely low concentrations. The "rotten egg" smell is a safety feature that lets people notice a leak (US Energy Information Administration).

63. Carbon monoxide alarms

Carbon monoxide is a colourless, odourless, poisonous gas produced by incomplete burning. Many alarms use an electrochemical cell in which carbon monoxide reacts at an electrode, producing a current that rises with the gas concentration and triggers the alarm.

64. Silica gel packets

The small packets in shoe boxes and electronics contain silica gel, a form of silicon dioxide full of microscopic pores with a huge internal surface area. Water vapour sticks to these surfaces, keeping the surrounding air dry and preventing mould and corrosion.

65. Safety matches

A safety match head contains an oxidiser such as potassium chlorate, and the strip on the box contains red phosphorus. Friction converts a little phosphorus into a reactive form that ignites the head. Separating the two chemicals is what makes the match "safe".

66. Glow sticks

Bending a glow stick breaks an inner glass vial, mixing hydrogen peroxide with a chemical called an oxalate ester. Their reaction releases energy that excites a dye, which gives off light. This is chemiluminescence: light from a chemical reaction rather than from heat.

67. Fireworks colours

The colours in fireworks come from metal salts heated in the explosion. Each metal's electrons give off light at characteristic colours: strontium for red, barium for green, copper for blue and sodium for yellow. Chemists use the same principle in flame tests to identify metals.

Farming and food supply

Feeding more than eight billion people depends on soil science, chemistry and genetics (FAO).

68. Nitrogen fertilisers

The Haber–Bosch process combines nitrogen from the air with hydrogen to make ammonia, the basis of most nitrogen fertiliser. Fertilisers made this way are estimated to support food production for around half the world's population. Too much fertiliser, though, washes into rivers and causes algal blooms.

69. Legumes and crop rotation

Peas, beans and clover host bacteria called rhizobia in nodules on their roots. The bacteria turn nitrogen from the air into forms the plant can use. Rotating these crops with cereals returns nitrogen to the soil naturally and reduces the need for fertiliser.

70. Soil testing

Farmers and gardeners test soil for pH and nutrients such as nitrogen, phosphorus and potassium. Most crops grow best in slightly acidic to neutral soil, and adding lime raises pH. Testing means fertiliser is used only where it is needed, saving money and protecting rivers.

71. Plant breeding

Most modern crops come from careful breeding: crossing plants with useful traits and selecting the best offspring over many generations. The high-yielding, disease-resistant wheat and rice varieties of the "Green Revolution" in the 1960s greatly increased harvests in Asia and Latin America.

72. Genetically modified crops

Genetic engineering adds or changes specific genes in a crop. Bt crops carry a gene from the bacterium Bacillus thuringiensis that makes a protein toxic to certain insect pests but not to people, reducing insecticide spraying. Newer gene-editing methods can make precise changes without adding foreign DNA.

73. Integrated pest management

Rather than spraying on a schedule, integrated pest management combines monitoring, natural predators, resistant varieties and crop rotation, and uses pesticides only when pests pass a threshold. It reduces costs, chemical use and the evolution of pesticide resistance (US EPA).

74. Drip irrigation

Drip systems deliver water slowly, directly to plant roots, through pipes with small emitters. Far less water is lost to evaporation and runoff than with flood or sprinkler irrigation, which matters because farming uses most of the world's fresh water withdrawals.

75. Hydroponics

Hydroponic farms grow plants without soil, with their roots in a water solution containing exactly the nutrients they need. Combined with LED lighting in indoor "vertical farms", this lets leafy greens and herbs be grown close to cities with less water.

76. Pollination

About three-quarters of leading food crop types benefit at least partly from animal pollination, mainly by bees. Farmers rent honeybee hives for crops such as almonds and apples, and research on wild pollinators guides the planting of wildflower strips near fields.

77. Food safety testing

Food producers and regulators test for contamination by bacteria such as Salmonella, Listeria and E. coli, using cultures, antibody tests and DNA methods. Genetic fingerprinting of bacteria lets health agencies link cases of food poisoning in different places to the same source and recall the food.

Water and the environment

Clean water and air are achievements of applied chemistry and biology (US EPA; USGS Water Science School).

78. Drinking water treatment

Treatment works add a coagulant such as aluminium sulphate, which makes tiny suspended particles clump together and settle. The water is then filtered through sand and disinfected, usually with chlorine, chloramine, ozone or ultraviolet light. Chlorination of drinking water dramatically reduced diseases such as typhoid and cholera.

79. Sewage treatment

Wastewater treatment plants use microbes to clean water. In the activated sludge process, air is bubbled through sewage so that bacteria can eat the organic matter. The cleaned water is separated from the sludge and released into rivers or the sea.

80. Desalination

Many dry countries make drinking water from seawater by reverse osmosis: forcing seawater at high pressure through a membrane that lets water molecules through but holds back salt. It takes a lot of energy, and the concentrated brine left over must be disposed of carefully.

81. Catalytic converters

A car's catalytic converter uses platinum, palladium and rhodium on a honeycomb surface to convert carbon monoxide, unburnt fuel and nitrogen oxides into carbon dioxide, water and nitrogen. It has greatly reduced urban air pollution from petrol vehicles.

82. Cleaning power station emissions

Coal-burning power stations and factories often use "scrubbers" that spray limestone slurry into exhaust gases. The limestone reacts with sulphur dioxide, which causes acid rain, and turns it into gypsum, which can be used to make plasterboard.

83. Protecting the ozone layer

When scientists showed that CFCs from fridges and aerosols destroy stratospheric ozone, governments agreed the 1987 Montreal Protocol to phase them out. Scientific assessments project that the ozone layer will recover to 1980 levels around the middle of this century, later over Antarctica (UNEP).

84. Composting

Composting puts decomposer microbes to work. Mixing nitrogen-rich "greens" with carbon-rich "browns", keeping the heap damp and turning it to add oxygen lets bacteria and fungi break waste down into nutrient-rich compost, keeping food waste out of landfill, where it would produce methane.

85. Bioremediation

Some bacteria can break down oil, solvents and other pollutants. After oil spills or at contaminated industrial sites, cleanup teams sometimes add nutrients to help these natural microbes work faster. Plants that absorb metals from soil are also used to clean up some sites.

86. Air quality forecasts

Air-quality indices combine measurements of pollutants such as fine particles, ozone and nitrogen dioxide into a single number, with health advice for each level. Forecasts based on weather and emissions models warn people with asthma or heart disease to limit outdoor exercise on bad days (AirNow).

87. Weather forecasting

Forecasts come from computer models that divide the atmosphere into a 3D grid and use the laws of physics and chemistry to calculate how temperature, pressure, wind and moisture will change. Millions of observations from satellites, balloons and weather stations feed the models every day. Modern forecasts several days ahead are far more accurate than those of a few decades ago.

Transport and energy

Moving people and goods relies on fuel chemistry, rubber and electrochemistry.

88. Petrol and octane ratings

Petrol is a blend of hydrocarbons refined from crude oil. Its octane rating measures how well it resists igniting too early under compression, which causes engine "knocking". Refiners blend components to reach the octane rating engines need.

89. Biofuels

Bioethanol is made by fermenting sugars from crops such as sugar cane and maize with yeast, the same process as brewing, and is blended into petrol. Biodiesel is made by reacting vegetable oils or waste cooking oil with an alcohol. Whether a biofuel reduces emissions overall depends on how its crops are grown.

90. Hydrogen fuel cells

A fuel cell combines hydrogen and oxygen from the air to produce electricity, with water as the only product at the vehicle. Unlike a battery, it keeps working as long as it is supplied with fuel. Its environmental benefit depends on how the hydrogen is made.

91. Tyres

Natural rubber is soft and sticky in heat and brittle in cold. Vulcanisation, discovered by Charles Goodyear in 1839, heats rubber with sulphur, which forms cross-links between the polymer chains and makes it tough and elastic. Modern tyres also contain carbon black and silica for strength and grip.

92. Antifreeze

Engine coolant contains ethylene glycol or propylene glycol mixed with water. Dissolved glycol lowers the freezing point and raises the boiling point of the coolant, protecting the engine in winter and summer. Ethylene glycol is poisonous, so spills must be cleaned up and kept away from pets.

93. Road salt and de-icers

Salt spread on roads dissolves in the thin film of water on ice, forming brine with a lower freezing point, so the ice melts at temperatures below 0 °C. Salt becomes less effective in very cold weather, when calcium chloride works better. It also speeds up rusting of cars and bridges.

94. Airbag inflation

When a crash sensor triggers an airbag, a small charge sets off a rapid chemical reaction that produces a large volume of gas, inflating the bag in a few hundredths of a second. Early systems used sodium azide, which produces nitrogen; modern inflators use other propellants or stored gas.

Safety, justice and society

Science also helps solve crimes, date the past and protect communities.

95. DNA profiling

Forensic scientists compare short repeated sections of DNA, called short tandem repeats, at a set of locations in the genome. The pattern is extremely unlikely to match between unrelated people, so it can link a suspect to evidence or exonerate an innocent person.

96. Fingerprint detection

Invisible fingerprints are made of sweat and skin oils. Forensic teams reveal them with fine powders, with chemicals such as ninhydrin, which reacts with amino acids in sweat to turn purple, or with superglue fumes, which polymerise on the ridges.

97. Testing for alcohol and drugs

Roadside breath tests often use fuel cells that oxidise alcohol in the breath and produce a current proportional to its concentration. Laboratories confirm results for alcohol and drugs using chromatography and mass spectrometry, which separate and identify molecules by their mass.

98. Radiocarbon dating

Living things take in carbon-14, which then decays at a known rate after they die. Measuring how much is left dates wood, bone, textiles and charcoal up to around 50,000 years old, helping archaeologists build accurate timelines of human history.

99. Earthquake early warning

Systems such as ShakeAlert on the US West Coast detect the fast, weaker P-waves at the start of an earthquake and send alerts before the slower, more damaging S-waves and surface waves arrive. A few seconds' warning is enough to stop trains and let people take cover (USGS).

100. Volcano monitoring

Scientists watch volcanoes for small earthquakes, ground swelling measured by GPS and satellites, and changes in gases such as sulphur dioxide. These signs of rising magma allow warnings and evacuations before many eruptions.

How to see the science around you

Once you know what to look for, you will find applied science everywhere. Three habits help:

  • Read labels. Ingredient lists on food, cleaning products and cosmetics name the chemicals doing the work, such as enzymes, surfactants and preservatives.
  • Ask what is changing. If something gets warmer, fizzes, changes colour or sets hard, a chemical reaction is probably happening.
  • Look for the invisible helpers. Microbes make your bread, cheese and yoghurt, clean your sewage and, occasionally, make you ill.

Where to go next

References

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