Physics Science

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

How physics makes 100 everyday things work, from microwaves, touchscreens and GPS to MRI scanners, golf balls and rainbows, explained room by room.

By BlogAI Editors · · 27 min read

Physics is not just something in a textbook. It is why your microwave heats soup, why your phone knows which way up it is, why a seatbelt saves lives and why the sky is blue. This guide walks through 100 applications of physics in everyday life, grouped by where you meet them: the kitchen, the home, your devices, transport, healthcare, sport, energy, the weather, buildings and space.

Each entry names the everyday thing, explains the physics that makes it work in plain language, and names the underlying principle so you can look it up. Where a claim depends on a specific fact, it links to a primary source such as NASA, NOAA, the U.S. FDA, the NIH or the U.S. Department of Energy.

How this guide relates to our other physics articles. This article starts from things you use and works back to the physics. Our 100 physics concepts explained with real-world examples does the reverse: it starts from each concept and gives an example. Read them together if you are revising. Technical details here are simplified for a general reader, and designs vary between manufacturers and models.

In the kitchen

1. Microwave ovens

A magnetron inside the oven produces microwaves that bounce around the metal box and are absorbed by food, mainly by water molecules, which are made to rotate back and forth and heat the food (U.S. FDA). Most household ovens operate at about 2.45 GHz. The metal mesh in the door has holes much smaller than the microwaves' wavelength (about 12 cm), so microwaves cannot get out but visible light can.

Principles: electromagnetic waves, dielectric heating, standing waves.

2. Induction hobs

A coil under the glass carries a rapidly alternating current, which creates a changing magnetic field. That field induces swirling electric currents in the base of a steel or iron pan, and the pan's resistance turns them into heat. The glass itself is only warmed by the hot pan. Aluminium and copper pans do not work on most induction hobs unless they have a magnetic base.

Principles: electromagnetic induction, eddy currents, resistive heating.

3. Refrigerators and freezers

A fridge does not make cold; it moves heat out. A refrigerant evaporates in pipes inside, absorbing latent heat from the food compartment. A compressor then squeezes the vapour, raising its temperature, and it releases that heat through the coils at the back as it condenses. That is why the back of a fridge feels warm.

Principles: latent heat, the second law of thermodynamics, heat pumps.

4. Pressure cookers

Water's boiling point rises with pressure. Sealing the pot and letting steam build up to about one atmosphere above normal pressure raises the boiling point to roughly 120 °C, so food cooks much faster than in an open pan at 100 °C.

Principles: vapour pressure, the relationship between pressure and boiling point.

5. Cooking at high altitude

Air pressure falls with height, so water boils at a lower temperature, by roughly 1 °C for every 300 m of altitude. In a city about 1,600 m above sea level, water boils at around 95 °C, which is why pasta and boiled eggs take longer and some recipes are adjusted.

Principles: atmospheric pressure, boiling point.

6. Electric kettles

A high-resistance heating element converts electrical energy into heat. The element sits at the bottom so that convection currents carry heat through the whole volume of water. An automatic switch turns the kettle off once steam reaches a sensor, often a bimetallic strip that bends as it heats because its two metals expand by different amounts.

Principles: Joule heating, convection, thermal expansion.

7. Toasters

Toaster elements are thin wires that glow red-hot. They heat the bread mainly by infrared radiation rather than by touching it. Many older pop-up toasters also use a bimetallic strip or an electronic timer to release the bread.

Principles: resistive heating, thermal radiation.

8. Vacuum flasks

A vacuum flask has two walls with a near-vacuum between them, which almost eliminates conduction and convection. The inner surfaces are silvered to reflect thermal radiation, and the stopper limits evaporation. The same design keeps cold drinks cold.

Principles: conduction, convection, radiation.

9. Fan ovens

A fan circulates hot air around the food. Moving air carries heat to the food's surface faster than still air, so fan ovens can cook at a lower set temperature than conventional ovens.

Principles: forced convection.

10. Sharp knives

A sharp edge concentrates the force from your hand onto a tiny area, producing a very high pressure that separates the food. A blunt knife spreads the same force over a wider area, so you push harder and it is more likely to slip.

Principles: pressure = force ÷ area.

11. Digital kitchen scales

Under the platform is a load cell: a small metal beam fitted with a strain gauge, a thin wire pattern whose electrical resistance changes slightly when the beam bends. The electronics convert that tiny resistance change into a weight reading.

Principles: elasticity, electrical resistance.

Around the home

12. LED light bulbs

In a light-emitting diode, electrons crossing a junction between two kinds of semiconductor drop to a lower energy level and give off the difference as light. LEDs waste far less energy as heat than incandescent bulbs, so they use much less electricity for the same light (U.S. Department of Energy).

Principles: semiconductors, energy levels, efficiency.

13. Smoke alarms

Ionisation smoke alarms contain a tiny sealed amount of americium-241, which emits alpha particles that ionise the air in a small chamber so that a small current flows. Smoke particles disrupt the current and trigger the alarm (U.S. NRC). Photoelectric alarms instead detect smoke scattering light from an LED onto a sensor.

Principles: radioactivity, ionisation, light scattering.

14. Washing machine spin cycles

During the spin cycle, the drum turns at high speed. The drum wall pushes the clothes round in a circle, but water can pass through the holes and keep moving in straight lines, away from the clothes.

Principles: circular motion, inertia.

15. Vacuum cleaners

A motor spins a fan that pushes air out of the cleaner, lowering the air pressure inside. Higher atmospheric pressure outside then pushes air, and dust, in through the nozzle.

Principles: air pressure, pressure differences.

16. Fuses, circuit breakers and RCDs

A fuse contains a thin wire that melts if too much current flows. A circuit breaker uses a bimetallic strip or an electromagnet to trip a switch. A residual-current device (RCD, called a GFCI in North America) compares the current in the live and neutral wires and cuts the power within a fraction of a second if they differ, which could mean current is leaking through a person.

Principles: heating effect of current, electromagnetism, conservation of charge.

17. Double glazing and insulation

Double-glazed windows trap a layer of air or an inert gas between two panes. Still gas is a poor conductor of heat, so the window loses much less heat than a single pane. Loft insulation and wool clothing work the same way by trapping air in fibres.

Principles: thermal conduction, convection.

18. Thermostats

A thermostat switches heating or cooling on and off to hold a set temperature. Older ones use a bimetallic strip that bends with temperature; modern ones use electronic sensors called thermistors, whose resistance changes predictably with temperature.

Principles: thermal expansion, temperature-dependent resistance, feedback control.

19. Loudspeakers

A coil of wire attached to a cone sits in the field of a permanent magnet. The audio signal is a varying current, so the force between the coil and the magnet varies too, pushing the cone back and forth to create sound waves.

Principles: the motor effect, sound waves.

20. Microphones

Many microphones work like loudspeakers in reverse: sound moves a diaphragm, and a coil attached to it moves in a magnetic field, inducing a voltage. Phone microphones are usually tiny MEMS capacitor microphones, where sound changes the gap between two plates and therefore their capacitance.

Principles: electromagnetic induction, capacitance.

21. Noise-cancelling headphones

Microphones on the headphones pick up outside noise, and electronics produce a sound wave that is its mirror image. When the two waves meet, they interfere destructively and largely cancel. It works best for steady, low-pitched sounds such as engine hum.

Principles: superposition, destructive interference.

22. Make-up and shaving mirrors

A concave mirror forms a magnified, upright image when your face is closer to it than its focal point. Car passenger-side mirrors use convex mirrors instead, which give a wider but smaller view, hence the warning that objects are closer than they appear.

Principles: reflection, curved mirrors.

23. Door handles, scissors and spanners

All are levers. A door handle sits far from the hinge to give a large torque from a small push. Cutting thick card near the pivot of the scissors is easier for the same reason.

Principles: torque, levers, mechanical advantage.

24. Water towers and household water pressure

Many towns pump water up into elevated tanks or towers. The weight of the water column creates pressure in the pipes below, so water flows out of taps even during a power cut. Upper floors of tall buildings often need extra pumps.

Principles: hydrostatic pressure, P=ρghP = \rho g h.

Phones, computers and communication

25. Touchscreens

Most phone and tablet screens are capacitive. A grid of transparent conductors under the glass forms an array of tiny capacitors. Your finger conducts and changes the electric field, and so the capacitance, where you touch. That is why ordinary gloves usually do not work.

Principles: capacitance, electric fields.

26. Phone motion sensors

Phones contain microscopic MEMS (micro-electromechanical systems) accelerometers: tiny masses on springs whose movement changes a capacitance. Gyroscopes in phones use vibrating structures that are deflected by the Coriolis effect when the phone rotates. Together they rotate the screen, count steps and stabilise camera images.

Principles: Newton's second law, springs, capacitance, rotating frames.

27. Digital cameras

Each pixel of an image sensor is a tiny photodiode. Photons striking it free electrons by the photoelectric effect, and the amount of charge collected tells the camera how bright that point was. Colour filters over the pixels record red, green and blue separately.

Principles: the photoelectric effect, semiconductors.

28. Rechargeable lithium-ion batteries

When the battery charges, lithium ions are pushed into one electrode; when it discharges, they flow back through the electrolyte while electrons flow through your phone's circuits. Battery capacity in milliamp-hours measures how much charge it can deliver.

Principles: electrochemistry, electric current, energy storage.

29. Wireless phone charging

A coil in the charging pad carries alternating current, creating a changing magnetic field. A matching coil in the phone picks up that changing field, which induces a current that charges the battery. The coils must be close and aligned, which is why position matters.

Principles: electromagnetic induction, transformers.

30. Wi-Fi, Bluetooth and mobile networks

All are radio communication. Data is encoded by changing the amplitude, frequency or phase of radio waves. Wi-Fi uses bands around 2.4 GHz, 5 GHz and, in newer routers, 6 GHz. Higher frequencies can carry more data but pass through walls less well.

Principles: electromagnetic waves, modulation, absorption.

31. Fibre-optic internet

Data travels as pulses of infrared light through hair-thin glass fibres. The light stays inside by total internal reflection, bouncing along the core even around gentle bends. In glass, light travels at about two-thirds of its speed in a vacuum.

Principles: refraction, total internal reflection.

32. GPS and satellite navigation

Your phone measures the time it takes signals to arrive from several satellites and works out its position from the differences. Timing must be extremely precise, and the system corrects for relativity: without corrections, satellite clocks would drift by about 38 microseconds a day relative to clocks on the ground (Ashby, Physics Today).

Principles: speed of light, special and general relativity.

33. TV remote controls

The remote flashes an infrared LED in coded patterns. Infrared is invisible to the eye, but most phone cameras can see it: point a remote at your camera and press a button.

Principles: infrared radiation, digital signals.

34. Barcode scanners

A scanner shines red light across the barcode. Black bars absorb it and white spaces reflect it, and a light sensor converts the pattern of reflections into a number. Camera-based scanners decode the same pattern from an image.

Principles: reflection and absorption of light.

35. LCD and OLED screens

An LCD screen has a backlight shining through polarising filters and a layer of liquid crystals. Voltages twist the crystals to control how much light passes through each sub-pixel. OLED screens have no backlight: each pixel is a tiny organic LED that makes its own light, so black pixels are fully off.

Principles: polarisation, electroluminescence.

36. Hard drives and flash storage

A hard disk stores bits as tiny magnetised regions on a spinning platter, written and read by a head floating just above the surface. Solid-state drives and phone storage use flash memory, which stores bits as trapped electric charge; writing and erasing relies on electrons tunnelling through a thin insulating layer, a quantum effect.

Principles: magnetism, quantum tunnelling.

37. Computer chips

Processors contain billions of transistors, tiny semiconductor switches that are turned on and off by a voltage on a control electrode. All computing is built from very fast patterns of these switches.

Principles: semiconductors, electric fields.

38. Quartz watches

A tiny quartz crystal shaped like a tuning fork vibrates when a voltage is applied, and produces a voltage as it vibrates. It is cut to resonate at 32,768 Hz, which is 2152^{15}, so a simple circuit can halve the frequency 15 times to get exactly one tick per second.

Principles: the piezoelectric effect, resonance.

Getting around

39. Seatbelts and airbags

In a crash, your body keeps moving forward at the car's speed. A seatbelt applies the force to stop you across your strong hip and chest bones, and an airbag inflates to spread the stopping force and lengthen the stopping time. A longer stopping time means a smaller force for the same change in momentum.

Principles: inertia, impulse and momentum.

40. Crumple zones and helmets

The front and rear of a car are designed to collapse in a controlled way. Crumpling takes time and absorbs kinetic energy, reducing the force on the people inside. A bicycle helmet's foam liner does the same for your head by crushing on impact.

Principles: impulse, energy absorption.

41. Hydraulic brakes

Pressing the brake pedal pushes a small piston in a cylinder of brake fluid. The pressure is transmitted through the fluid to larger pistons at each wheel, which press pads against the brake discs with much greater force. Friction then turns the car's kinetic energy into heat.

Principles: Pascal's principle, friction, energy conversion.

42. Anti-lock braking systems (ABS)

Sensors detect when a wheel is about to lock and skid, and the system rapidly pulses the brake pressure on that wheel. A rolling tyre grips with static friction, which is usually stronger than the kinetic friction of a skidding tyre, and a rolling wheel still lets you steer.

Principles: static vs kinetic friction.

43. Tyre tread

On a dry road, a smooth tyre would grip well, which is why racing cars use "slicks". On wet roads, tread grooves channel water out from under the tyre. Without them, a layer of water can lift the tyre off the road, called aquaplaning or hydroplaning, and grip disappears.

Principles: friction, fluid pressure.

44. Regenerative braking

Electric and hybrid cars slow down partly by running their electric motors as generators. The car's kinetic energy is converted back into electrical energy and stored in the battery instead of being wasted as heat in the brakes.

Principles: electromagnetic induction, conservation of energy.

45. Electric motors in cars, fans and drills

A motor turns because of the force on current-carrying wires in a magnetic field. Changing the current direction at the right moments, either with brushes or with electronics, keeps the rotor turning.

Principles: the motor effect, magnetic forces.

46. Petrol and diesel engines

Burning fuel heats gas in a cylinder, the gas expands and pushes a piston, and a crankshaft converts the up-and-down motion into rotation. As heat engines, they are limited by thermodynamics: much of the fuel's energy is lost as heat through the exhaust and radiator.

Principles: thermodynamics, heat engines, gas laws.

47. Aerodynamic car design

At motorway speeds, air resistance is the main force a car must overcome, and it grows roughly with the square of speed. Smooth, tapered shapes reduce drag, improving fuel economy and the range of electric cars.

Principles: drag, fluid dynamics.

48. Aeroplane wings

A wing is shaped and angled so that it deflects air downwards. By Newton's third law, the air pushes the wing up. The airflow also creates lower pressure above the wing than below. The common "equal transit time" explanation, which says air over the top must meet air from below at the trailing edge, is incorrect (NASA Glenn Research Center).

Principles: Newton's third law, Bernoulli's principle, pressure.

49. Jet engines

A jet engine sucks in air, compresses it, burns fuel in it and blasts the hot gas out of the back at high speed. Pushing a large mass of gas backwards produces an equal and opposite forward thrust.

Principles: Newton's third law, conservation of momentum, thermodynamics.

50. Bicycles

Gears change the ratio between how fast you pedal and how fast the wheel turns, trading force for speed. Steering, the geometry of the front fork and, at higher speeds, the gyroscopic effect of the wheels all help a moving bicycle stay upright.

Principles: gear ratios, torque, angular momentum.

51. Ships and submarines

A steel ship floats because its hull displaces a weight of water equal to its own weight. A submarine dives by flooding ballast tanks with water to increase its average density, and surfaces by blowing the water out with compressed air.

Principles: Archimedes' principle, density.

52. Speed cameras and radar guns

A radar gun sends out radio waves that reflect off a moving vehicle. The reflected waves come back at a slightly shifted frequency, and the shift tells the gun the vehicle's speed. Lidar guns use the travel time of laser pulses instead.

Principles: the Doppler effect, speed of light.

Health and medicine

53. X-ray imaging

X-rays are high-energy electromagnetic waves that pass through soft tissue more easily than through bone, which contains heavier elements such as calcium. Bones cast a "shadow" on the detector, showing fractures.

Principles: electromagnetic spectrum, absorption of radiation.

54. CT scans

A computed tomography scanner rotates an X-ray source and detectors around the body, taking many images from different angles. A computer combines them into cross-sectional slices, showing soft tissue detail that a single X-ray cannot.

Principles: X-ray absorption, mathematical reconstruction.

55. MRI scanners

MRI uses a powerful magnet to align protons, mainly in the body's water. Radio-frequency pulses knock them out of alignment, and as they realign they emit signals that are used to build detailed images, without ionising radiation (NIH National Institute of Biomedical Imaging and Bioengineering). The strong field is why metal objects must stay out of the scanner room.

Principles: nuclear magnetic resonance, electromagnetism.

56. Ultrasound scans

A probe sends high-frequency sound, far above human hearing, into the body and listens for echoes from boundaries between tissues. The timing of echoes gives depth, building an image. Doppler ultrasound measures blood flow from frequency shifts.

Principles: sound waves, reflection, the Doppler effect.

57. PET scans

Positron emission tomography uses a tracer that emits positrons, the antimatter partner of electrons. Each positron meets an electron and both annihilate, producing two gamma rays travelling in opposite directions. Detectors around the body locate where this happened, showing where the tracer collected.

Principles: antimatter, E=mc2E = mc^2, gamma radiation.

58. Radiotherapy

Beams of high-energy X-rays or particles are aimed at a tumour from several directions. Each beam alone is weaker, but where they overlap the dose is high enough to damage cancer cells, while sparing more of the healthy tissue around them.

Principles: ionising radiation, energy deposition.

59. Infrared thermometers

Every object gives off infrared radiation that depends on its temperature. Ear and forehead thermometers measure this radiation and convert it to a temperature reading without needing to touch for long.

Principles: thermal radiation, the Stefan–Boltzmann law.

60. Pulse oximeters

A clip on your finger shines red and infrared light through it. Oxygen-rich and oxygen-poor haemoglobin absorb these two wavelengths differently, so comparing them estimates blood oxygen saturation. The U.S. FDA has been examining evidence that pulse oximeters can be less accurate in people with darker skin pigmentation, and advises not to rely on a pulse oximeter alone (U.S. FDA).

Principles: light absorption, spectroscopy.

61. Glasses and contact lenses

Short-sighted eyes focus light in front of the retina; a diverging (concave) lens corrects this. Long-sighted eyes focus behind it; a converging (convex) lens corrects that. Lens strength is measured in dioptres.

Principles: refraction, lenses.

62. Laser eye surgery

A laser reshapes the cornea, the clear front surface of the eye, by removing microscopic amounts of tissue. Changing its curvature changes how strongly it refracts light, which can correct vision without glasses.

Principles: refraction, lasers.

63. ECG heart monitors

Each heartbeat is triggered by electrical signals in the heart muscle. Electrodes on the skin detect the tiny voltage changes these signals produce, and the resulting trace helps doctors spot irregular rhythms.

Principles: electric potential, voltage.

64. Blood pressure monitors

A cuff around the arm is inflated until it squeezes the artery closed, then slowly released. The pressure at which blood starts to flow again and the pressure at which flow becomes smooth give the two readings, measured in millimetres of mercury.

Principles: fluid pressure, pressure measurement.

65. Defibrillators

A defibrillator charges a capacitor and then releases its stored energy through the chest in a few milliseconds. The pulse of current can stop a dangerous irregular heart rhythm and let the heart's natural rhythm restart.

Principles: capacitors, stored electrical energy.

Sport and play

66. Curving free kicks and spinning balls

A spinning ball drags air around with it, deflecting the airflow to one side. The air pushes back on the ball, curving its path. This is the Magnus effect, used in football free kicks, tennis topspin and baseball curveballs.

Principles: the Magnus effect, Newton's third law.

67. Dimples on golf balls

Dimples make the thin layer of air next to the ball turbulent. A turbulent layer clings to the ball's surface for longer, so the low-pressure wake behind the ball is smaller and drag is lower. A dimpled ball flies much further than a smooth one.

Principles: boundary layers, drag.

68. High jump and pole vault

In the Fosbury flop, the jumper arches so that their centre of mass can stay below the bar while their body passes over it. A pole vaulter converts running kinetic energy into elastic energy in the bending pole, then into gravitational potential energy.

Principles: centre of mass, energy conversion.

69. Running shoes and tracks

Cushioned soles spread impact forces over a longer time. Modern racing shoes add stiff plates and springy foams designed to return more of the energy stored when the foam is compressed. Running tracks use rubbery surfaces for similar reasons.

Principles: impulse, elastic potential energy.

70. Swimming

Swimmers push water backwards with their hands and feet, and the water pushes them forwards. Streamlined body positions and smooth swimsuits reduce drag, which is the main force slowing a swimmer.

Principles: Newton's third law, drag.

71. Drafting in cycling and running

Riding or running close behind someone puts you in their slipstream, where the air is already moving forward and drag is lower. That is why cyclists ride in a tight group, or peloton, and take turns at the front.

Principles: drag, fluid flow.

72. Bows and arrows

Drawing a bow stores elastic potential energy in its limbs. Releasing the string converts most of that energy into the arrow's kinetic energy. The arrow then follows a projectile path, so archers aim slightly above a distant target.

Principles: elastic potential energy, projectile motion.

73. Diving, gymnastics and figure skating

Once a diver leaves the board, their angular momentum is fixed. Tucking into a ball reduces their moment of inertia so they spin faster; opening out slows the spin for a clean entry. Skaters pull their arms in for the same effect.

Principles: conservation of angular momentum.

74. Ice skating

Ice is slippery because a very thin liquid-like layer forms on its surface. The once-common explanation, that the pressure of the blade melts the ice, does not hold for most skating conditions, and the exact mechanism is still being researched. The blade's narrow edge also gives high pressure for grip when turning.

Principles: friction, phase changes, pressure.

75. Trampolines

As you land, the springs or elastic bands stretch and store elastic potential energy, which is released to push you back up. Bending your knees at the right moment adds energy each bounce, much like pumping a swing.

Principles: elastic potential energy, energy conversion, resonance.

Energy and power

76. Power station generators

Most electricity is generated by spinning a magnet inside coils of wire, or coils inside a magnet. The changing magnetic field induces a voltage. Steam from burning fuel or nuclear reactions, falling water or wind provides the spin.

Principles: electromagnetic induction, Faraday's law.

77. Transformers and the power grid

The grid transmits electricity at very high voltages, because for the same power a higher voltage means a lower current, and the energy lost as heat in the wires depends on the current squared. Transformers step the voltage up for transmission and down for homes.

Principles: electrical power, transformers, P=I2RP = I^2R.

78. Solar panels

Solar cells are made of semiconductors such as silicon. Photons from sunlight free electrons, and the structure of the cell drives them through an external circuit as current.

Principles: the photovoltaic effect, semiconductors.

79. Wind turbines

Wind pushes on the turbine blades, which are shaped like aircraft wings to produce lift and turn the rotor. A gearbox or a direct-drive generator converts the rotation into electricity. The power available in wind grows with the cube of wind speed, so doubling the wind speed gives roughly eight times as much power.

Principles: kinetic energy of fluids, lift, induction.

80. Hydroelectric dams

Water stored behind a dam has gravitational potential energy. As it falls through pipes to the turbines below, that energy becomes kinetic energy and then electricity. The taller the drop, the more energy each litre carries.

Principles: gravitational potential energy, energy conversion.

81. Pumped-storage hydropower

When electricity is plentiful, some power stations pump water up into a high reservoir. When demand peaks, the water flows back down through turbines. It works like a giant rechargeable battery that stores energy as height.

Principles: gravitational potential energy, efficiency.

82. Nuclear power

Splitting a uranium-235 nucleus with a neutron releases energy and more neutrons, which can split further nuclei in a controlled chain reaction. The heat produces steam to drive turbines. The products have slightly less mass than the starting materials, and that mass difference is the energy released.

Principles: nuclear fission, E=mc2E = mc^2.

83. Heat pumps

A heat pump is a refrigerator run in reverse: it collects heat from outdoor air or the ground and releases it inside, even when it is cold outside. Because it moves heat rather than generating it, it can deliver up to about three times more heat than the electricity it uses (ENERGY STAR).

Principles: thermodynamics, latent heat.

84. Geothermal energy

Earth's interior is hot, partly from heat left over from its formation and partly from radioactive decay. In some regions, hot water and steam from underground drive turbines, or are used directly for heating.

Principles: heat transfer, radioactivity.

85. Solar water heating

Rooftop solar thermal collectors are dark panels that absorb sunlight and transfer its heat to water or a fluid pumped through them. Glass covers trap the heat, much like a greenhouse.

Principles: absorption of radiation, conduction, convection.

Weather and the natural world

86. Blue skies and red sunsets

Air molecules scatter short-wavelength blue light much more than red, so blue light reaches your eyes from all over the sky. At sunrise and sunset, sunlight passes through so much air that most of the blue is scattered away, leaving reds and oranges.

Principles: Rayleigh scattering.

87. Rainbows

Sunlight entering a raindrop is refracted, reflected off the back of the drop and refracted again on the way out. Each colour bends by a slightly different amount, so the colours separate. Rainbows always appear opposite the Sun, at about 42° from the point directly opposite it.

Principles: refraction, dispersion, reflection.

88. Lightning and thunder

Collisions between ice particles in storm clouds separate electric charge. When the voltage becomes large enough, the air breaks down and a giant spark flows. The lightning channel heats the air to temperatures several times hotter than the surface of the Sun for an instant (AIP Inside Science), and the air expands so fast it makes the shock wave we hear as thunder.

Principles: static electricity, electrical breakdown, sound waves.

89. Lightning conductors

A lightning conductor is a metal rod on top of a building connected by a thick conductor to the ground. If lightning strikes, the current takes this low-resistance path to earth instead of passing through the building's structure.

Principles: conductors, electric current.

90. Clouds and rain

As moist air rises, it expands because air pressure is lower higher up, and expanding air cools. When it cools to its dew point, water vapour condenses onto tiny particles of dust or salt to form cloud droplets, which can grow into raindrops.

Principles: adiabatic cooling, condensation, latent heat.

91. Sea breezes and winds

Land heats up faster than water on a sunny day, because water has a much higher specific heat capacity. Warm air over the land rises and cooler air from the sea flows in to replace it. At night the pattern can reverse.

Principles: specific heat capacity, convection.

92. The greenhouse effect

Earth's surface absorbs sunlight and gives off infrared radiation. Gases such as water vapour and carbon dioxide absorb and re-emit some of that infrared, keeping the surface warmer than it would otherwise be. Increasing these gases strengthens the effect (NASA Science).

Principles: thermal radiation, absorption spectra.

93. The seasons

Seasons happen because Earth's axis is tilted by about 23.5°. For part of the year a hemisphere leans towards the Sun and receives more direct sunlight for more hours each day. Earth is actually closest to the Sun in early January, during the northern winter (NASA Space Place).

Principles: angle of incidence, radiation intensity.

Buildings and structures

94. Bridges and expansion joints

Long bridges expand in summer and contract in winter. Expansion joints, the toothed or rubber-filled gaps you drive over, let the deck change length without cracking. Railway tracks and pipelines also allow for expansion.

Principles: thermal expansion.

95. Earthquake-resistant buildings

Engineers design buildings so that their natural frequencies avoid the shaking frequencies of likely earthquakes. Some buildings sit on base isolators, flexible bearings that let the ground move beneath them. Some skyscrapers, such as Taipei 101, have a huge tuned mass damper: a heavy pendulum that swings against the building's sway.

Principles: resonance, damping, inertia.

96. Lifts and counterweights

A lift car is connected by cables over a pulley to a heavy counterweight. The counterweight balances most of the car's weight, so the motor only needs to supply the difference, which saves energy.

Principles: forces in equilibrium, work and energy.

Space and satellites

97. Communication and weather satellites

A satellite at about 35,786 km above the equator takes the same time to orbit as Earth takes to rotate, so it stays above the same spot. This geostationary orbit is used for TV broadcasting and weather satellites. Lower satellites orbit faster and pass overhead.

Principles: Newton's law of gravitation, orbital motion, Kepler's third law.

98. Telescopes

Refracting telescopes use lenses and reflecting telescopes use curved mirrors to collect light and focus it. A larger opening collects more light and can show finer detail. Space telescopes avoid the blurring of Earth's atmosphere and can observe wavelengths, such as much of the infrared, that the atmosphere absorbs.

Principles: refraction, reflection, diffraction limits.

99. Rockets

A rocket carries both fuel and oxidiser and expels hot exhaust gas at high speed. The gas gains backward momentum, and the rocket gains equal forward momentum. Rockets work in the vacuum of space because they do not push against air.

Principles: Newton's third law, conservation of momentum.

100. Auroras and space weather

The Sun gives off a stream of charged particles called the solar wind. Earth's magnetic field steers some of these particles towards the polar regions, where they collide with oxygen and nitrogen in the upper atmosphere. The atoms are excited and give off light in specific colours, mostly green and red from oxygen (NOAA Space Weather Prediction Center).

Principles: magnetic forces on moving charges, atomic emission spectra.

How to spot physics around you

Once you know what to look for, physics shows up everywhere. A few questions to ask about any device or event:

  • Where does the energy come from, and where does it go? Almost every device converts energy from one form to another, and some always ends up as heat.
  • What forces are acting? If something speeds up, slows down or turns, there is a net force. Find it.
  • Is something moving in a field? Motors, generators, speakers and chargers all depend on electric and magnetic fields.
  • Is there a wave? Sound, light, radio, Wi-Fi and ultrasound all carry energy and information as waves.
  • What happens at the boundary? Reflection, refraction, friction and heat transfer all happen where two materials meet.

To try some of these ideas yourself, start with our 101 physics experiments you can do at home. If you want to investigate a device properly, many of the 101 physics projects for students begin with everyday technology, such as solar panels, motors and bicycle gears. To calculate what is going on, use 100 physics formulas every student should know. For more articles and blogs, browse the physics category.

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