Heavy things fall faster. There's no gravity in space. Lightning never strikes twice. You've heard them all, and they're (mostly) wrong. Here are the 50 most common physics myths, each with the truth, the physics behind it, and something to try at home.
🪶Heavy things fall faster (Galileo would like a word)
Two objects walk into a vacuum. Both hit the floor at the same time. Awkward for the bowling ball.
The myth
Heavier objects fall faster than lighter ones.
Myth or fact? Take a guess.
The truth
Without air, everything falls with the same acceleration (about 9.8 m/s²). In 1971 on the Moon, Apollo 15's David Scott dropped a hammer and a feather and they landed together.
The physics: Gravity pulls harder on a heavier object, but a heavier object also has more inertia, so the two effects cancel: a = F/m = g. In air, a feather is held back by drag, not by being light.
Try it at home: Drop a flat sheet of paper and the same sheet crumpled into a ball. Then rest the flat sheet on top of a book and drop the book: the paper falls just as fast as the book.
Aristotle believed it for about 2,000 years. Ice rinks disagree.
The myth
You need a constant force to keep something moving.
Myth or fact? Take a guess.
The truth
With no net force, an object keeps moving at constant velocity (Newton's first law). A sliding book stops because friction acts on it, not because nobody is pushing.
The physics: Force changes motion (it causes acceleration); it doesn't sustain it. On ice or in space, things glide on and on.
Try it at home: Slide a coin across a smooth table, then across a carpet. The surface decides how far it goes, not any hidden push.
🧑🚀There's no gravity in space (so why isn't the ISS flying away?)
Astronauts float. They also fall. Both are true at the same time.
The myth
Astronauts float on the space station because there's no gravity up there.
Myth or fact? Take a guess.
The truth
At the ISS's height, about 400 km up, gravity is still roughly 90% as strong as on the ground. Astronauts float because they and the station are in continuous free fall around Earth.
The physics: The station moves sideways at about 7.7 km/s, so as it falls towards Earth, the surface curves away beneath it. It is always falling and always missing.
Try it at home: You feel the same weightlessness at the top of a jump on a trampoline or on a drop ride: for a moment, everything around you falls with you.
⚖️If action and reaction cancel, how does anything move?
A horse pulling a cart has a very clever argument for not moving. It's wrong.
The myth
Action and reaction forces are equal and opposite, so they cancel and nothing could ever accelerate.
Myth or fact? Take a guess.
The truth
They act on different objects, so they can't cancel each other. Only forces acting on the same object can add up to zero.
The physics: When you push a wall, the wall pushes back on you, not on itself. When a rocket pushes gas downwards, the gas pushes the rocket upwards, and it's the force on the rocket that accelerates it.
Try it at home: On a wheeled chair or roller skates, push against a wall. You roll away because the wall pushed you.
The car turns left and you slide right. Nobody pushed you. You're just very committed to going straight.
The myth
In a turning car, a "centrifugal force" throws you outwards.
Myth or fact? Take a guess.
The truth
Your body just wants to keep moving in a straight line (inertia). The only real force is the inward push from the seat and door, the centripetal force. Centrifugal force isn't a real force in an inertial frame.
The physics: In the car's own rotating frame, physicists sometimes add a "centrifugal force" as a bookkeeping trick, but nothing on the road is actually pushing you outwards.
Try it at home: Whirl a ball on a string and let go. It flies off along a straight line, tangent to the circle, not outwards along the string.
Try walking without friction. Actually, don't. Watch someone on ice instead.
The myth
Friction is the enemy. It only ever slows things down.
Myth or fact? Take a guess.
The truth
Without friction you couldn't walk, drive, hold a pencil or tie a knot. The friction on a car's driving wheels is what pushes the car forwards.
The physics: Your foot pushes backwards on the ground, and static friction pushes you forwards. Wet floors and ice are dangerous precisely because friction is missing.
Try it at home: Walk in socks on a polished floor, then in shoes on a rough one (carefully). Notice how much easier it is to push off with friction.
A rolling race in which the mass doesn't matter, but your shape does.
The myth
A heavier ball rolls down a slope faster than a light one.
Myth or fact? Take a guess.
The truth
Mass doesn't matter, shape does. Two solid balls of any mass arrive together. A solid ball beats a solid cylinder, and a solid cylinder beats a hollow one.
The physics: Some energy goes into spinning. How much depends on how the mass is spread out (the moment of inertia), while the total mass cancels out.
Try it at home: Race a can of beans against a can of clear soup down a slope. The runny liquid doesn't spin along with the can, so the two usually finish differently.
It would sting. That's it. The coin is not a tiny meteor.
The myth
A coin dropped from the top of a skyscraper can punch through your skull.
Myth or fact? Take a guess.
The truth
Air drag caps its speed (terminal velocity) at something like 50–80 km/h. It would sting, but it won't injure you badly.
The physics: A small flat coin tumbles and catches a lot of air for its tiny mass, so drag balances its weight after a short fall.
Try it at home: Drop one coffee filter and a stack of five from the same height. The heavier stack falls faster, because it's drag, not gravity, that limits the speed.
A steel ship floats. A steel nail sinks. Same steel, different shape.
The myth
Heavy things sink and light things float.
Myth or fact? Take a guess.
The truth
Floating depends on average density, not weight. A giant steel ship floats while a tiny steel nail sinks.
The physics: An object floats if it can push aside a weight of water equal to its own (Archimedes' principle). A ship's hollow hull spreads its mass over a big volume, so its average density is less than water's.
Try it at home: Squash a lump of modelling clay into a ball, and it sinks. Shape it into a little boat, and it floats.
The air above the wing did not get a memo that it has to catch up.
The myth
Air going over the top of a wing has to travel farther, so it goes faster to meet the air below, which creates lift.
Myth or fact? Take a guess.
The truth
The "equal transit time" idea is wrong. The air over the top arrives first. Wings make lift by deflecting air downwards (Newton's third law) together with the pressure difference that comes with that.
The physics: Faster air over the curved top does mean lower pressure (Bernoulli), but the air speeds up because the wing is turning it, not because it needs to catch up. Flat paper planes and upside-down stunt planes fly too.
Try it at home: Hold a strip of paper under your lower lip and blow across the top of it. The paper rises.
Nothing sucks. The atmosphere pushes. It's a very heavy atmosphere.
The myth
A vacuum cleaner or a straw "sucks" things in.
Myth or fact? Take a guess.
The truth
There's no such thing as suction: the air outside pushes. Lowering the pressure inside lets the higher outside pressure push liquid or dust in.
The physics: Atmospheric pressure is about 100,000 pascals, roughly the weight of 10 tonnes on every square metre. That's also why a straw can't lift water more than about 10 metres, no matter how hard you suck.
Try it at home: Fill a glass to the brim, cover it with a card, and flip it over. The card stays put because the air pushes it up.
The bees never read the calculation. Lucky for the flowers.
The myth
Physics says a bumblebee can't fly.
Myth or fact? Take a guess.
The truth
This is an urban legend from a 1930s back-of-the-envelope calculation that treated a bee's wings like the fixed wing of an aeroplane. Bees flap and twist their wings, making vortices that give extra lift.
The physics: Insect flight uses unsteady aerodynamics, such as leading-edge vortices, which the simple fixed-wing model ignores.
Every tourist has tested this. The sink has no idea what hemisphere it's in.
The myth
Water swirls clockwise down a sink in the northern hemisphere and anticlockwise in the southern, because of Earth's rotation.
Myth or fact? Take a guess.
The truth
At sink size, the Coriolis effect is far too weak. The swirl direction is decided by the shape of the basin and leftover motion in the water. Coriolis does matter for huge systems like cyclones.
The physics: Earth's rotation is too slow compared with a sink's small size and short drain time to beat even a tiny bit of stirring.
Try it at home: Fill a sink, stir it gently one way, and pull the plug. Then do the opposite. The swirl follows your stirring.
A sparkler is hotter than your oven, and you can safely hold one. Explain that.
The myth
Heat and temperature are the same thing.
Myth or fact? Take a guess.
The truth
Temperature measures the average kinetic energy of particles. Heat is energy that transfers because of a temperature difference. A sparkler's sparks are over a thousand degrees but carry almost no heat, so they don't burn you.
The physics: Total thermal energy also depends on how much material there is. A bathtub of warm water holds far more heat than a cup of boiling water.
Then why does your pizza have a burning crust and a frozen middle?
The myth
Microwaves cook food from the inside out.
Myth or fact? Take a guess.
The truth
Microwaves only penetrate a few centimetres, so the outer layers heat first and the heat then spreads inwards by conduction. They also don't make food radioactive: microwaves are non-ionising.
The physics: That's why big lumps of food can be hot outside and cold in the middle, and why the standing time on the packet matters.
The fridge is not a very slow air conditioner. It's a heat pump with a hot back.
The myth
Leaving the fridge door open cools the kitchen.
Myth or fact? Take a guess.
The truth
It warms the kitchen slightly. A fridge moves heat from inside to outside through its back, and the electrical energy driving the compressor also ends up as heat in the room.
The physics: Energy conservation: the room gains all the heat removed from inside plus the work done by the compressor.
In the race between air and steel, steel is the express train and air is the slow bus.
The myth
Sound travels fastest through thin air and slower through dense water and solids.
Myth or fact? Take a guess.
The truth
Sound is about four times faster in water (about 1,500 m/s) than in air (about 340 m/s), and about fifteen times faster in steel (about 5,000 m/s).
The physics: Speed depends on how stiff a material is compared with how dense it is. Solids and liquids are much harder to squash than air, so waves pass along faster.
Try it at home: Press your ear to a long metal fence or railing while a friend taps the far end. You'll hear the tap through the metal before the air.
Lightning and thunder are twins born at the same time. One just takes the bus.
The myth
You hear thunder after you see lightning because lightning happens first.
Myth or fact? Take a guess.
The truth
They happen at the same moment. Light (about 300,000 km/s) is nearly a million times faster than sound (about 340 m/s), so you see the flash first and the boom later.
The physics: Count the seconds between the flash and the boom and divide by three to get the distance to the lightning in kilometres.
Try it at home: Next thunderstorm, count the seconds from flash to boom.
The prism is not adding anything. It's just a very good sorting machine.
The myth
A prism adds colours to white light.
Myth or fact? Take a guess.
The truth
White light is already a mixture of all the colours. A prism only separates them, because each colour bends by a slightly different amount.
The physics: Glass slows blue light a little more than red, so blue bends more (dispersion). Newton even used a second prism to recombine the colours into white light.
It's the other way round. The sea is blue because it's copying the sky.
The myth
The sky is blue because it reflects the ocean.
Myth or fact? Take a guess.
The truth
The sky is blue because air molecules scatter short (blue) wavelengths of sunlight much more than long (red) ones (Rayleigh scattering). The sea is partly blue because it reflects the sky, and because water absorbs red light.
The physics: Scattering strength goes as 1/λ⁴, so blue light is scattered nearly ten times more than red. At sunset, light travels through more air, the blue is scattered away, and the reds and oranges are left.
Try it at home: Add a few drops of milk to a glass of water and shine a torch through it: the side looks bluish and the light coming out looks orange.
Then why doesn't the mirror swap your head and your feet?
The myth
A mirror flips left and right.
Myth or fact? Take a guess.
The truth
A mirror flips front and back. Your right hand is still on the right-hand side of the mirror image. It's the image's "front" that faces you.
The physics: A plane mirror reverses only the direction perpendicular to its surface (depth). The left–right swap is how we imagine ourselves turning around to face our image.
The ambulance doesn't sing a different note. You just hear it differently.
The myth
A passing siren's pitch changes because the siren changes its note.
Myth or fact? Take a guess.
The truth
The siren emits a constant note. You hear a higher pitch as it approaches (the waves are bunched up) and a lower one as it moves away (the waves are stretched out).
The physics: This is the Doppler effect: the relative motion between source and listener changes the frequency you receive.
The stars are steady. It's the air that has the jitters.
The myth
Stars twinkle because their light flickers.
Myth or fact? Take a guess.
The truth
Stars shine steadily. Twinkling is caused by Earth's turbulent atmosphere bending their light this way and that. Planets twinkle much less. Astronauts see steady stars.
The physics: A star is effectively a point of light, so its beam is bent along one path that wobbles. A planet is a tiny disc, so its wobbles average out.
Try it at home: A star close to the horizon twinkles more: its light passes through more air.
Light in glass is a bit slower. Bad news for the speed-of-light fanclub.
The myth
Light always travels at 300,000 km/s.
Myth or fact? Take a guess.
The truth
That's its speed in a vacuum. In glass it slows to about two-thirds of that, and in water to about three-quarters. The slowing is why light bends (refraction).
The physics: The refractive index n = c/v is exactly that ratio: about 1.5 for glass and 1.33 for water.
If the bulb ate the current, the wire coming out of it would be very disappointed.
The myth
A bulb uses up the current.
Myth or fact? Take a guess.
The truth
In a series circuit, the current is the same before and after the bulb. The bulb transfers energy (as light and heat), but the charge isn't used up.
The physics: Charge is conserved: whatever flows into the bulb flows out again. The battery keeps pushing charge round the loop, and the energy goes into light and heat.
Electrons race through wires at the speed of light.
Myth or fact? Take a guess.
The truth
Individual electrons drift at less than a millimetre per second. What travels at nearly the speed of light is the electric signal (the field), which is why a lamp lights up instantly.
The physics: It's like a tube already full of marbles: push one in at one end and one pops out of the other end immediately.
The bird is not brave. The bird is at exactly one voltage.
The myth
Birds sit safely on power lines because the wires are insulated, or because they're lucky.
Myth or fact? Take a guess.
The truth
A bird sits at a single voltage, so there's almost no potential difference across its body and no current flows through it. Power lines are often bare wires. A bird touching two wires, or a wire and a pole, would be in trouble.
The physics: Current only flows when there's a potential difference across something. The bird's two feet are at (almost) the same potential.
It's a bit like saying "it's not the hill, it's the fall". Both matter.
The myth
Volts don't kill, amps do.
Myth or fact? Take a guess.
The truth
Half true. Current through the body does the harm, but the current is set by voltage divided by your body's resistance (I = V/R). A higher voltage can push more current through the same skin.
The physics: Dry skin has a high resistance and wet skin much less. A 9 V battery is safe because it can't push a dangerous current through dry skin, while mains voltage can.
The tyres are just there to roll. The metal roof is the hero.
The myth
A car is safe in a thunderstorm because its rubber tyres insulate it.
Myth or fact? Take a guess.
The truth
Tyres are far too thin to insulate against lightning. The car's metal body acts as a Faraday cage: the charge flows around the outside and to the ground, leaving the inside safe.
The physics: Excess charge sits on the outside of a conductor, and the field inside a closed metal shell is essentially zero. (Don't touch the metal.)
If batteries were full of electrons, a dead battery would weigh less. It doesn't.
The myth
A battery is a tank full of electrons that runs out when they're all used.
Myth or fact? Take a guess.
The truth
A battery stores chemical energy. Its chemical reactions push electrons that were already in the wire around the circuit. As many electrons return to the battery as leave it.
The physics: A flat battery has simply used up its chemical reactants.
Try a fridge magnet on a coin or a soft-drink can. Betrayal.
The myth
Magnets attract all metals.
Myth or fact? Take a guess.
The truth
Only a few metals: iron, nickel, cobalt and some alloys of them. Aluminium, copper, gold and silver aren't attracted, and many stainless steels aren't either.
The physics: Attraction needs a material with atoms whose tiny magnetic moments can line up (ferromagnetism). Most metals don't have that.
Try it at home: Test coins, aluminium foil, a steel paperclip and a soft-drink can with a fridge magnet.
Technically it points to a magnetic south pole that's sitting in the north. Physics likes trolling.
The myth
A compass points to Earth's magnetic north pole, so it's a north pole.
Myth or fact? Take a guess.
The truth
The compass needle's north-seeking end is attracted to the pole in the Arctic. Since opposite poles attract, Earth's magnetic pole near geographic north is really a magnetic south pole.
The physics: "North" on a magnet just means "north-seeking". Earth behaves like a giant bar magnet with its south pole near the north geographic pole.
Benjamin Franklin guessed wrong, and the whole world agreed to keep going.
The myth
Electric current is the flow of electrons, from the negative terminal to the positive one.
Myth or fact? Take a guess.
The truth
Half true. The electrons really do drift from negative to positive, but conventional current is drawn from positive to negative, the opposite way. It's a convention that works just as well.
The physics: Franklin guessed positive charge was the mover, long before electrons were discovered. By then the convention was in every textbook.
Earth is closest to the Sun in January. Tell that to a northern-hemisphere winter.
The myth
Summer happens because Earth is closer to the Sun.
Myth or fact? Take a guess.
The truth
Seasons come from Earth's 23.5° axial tilt, not distance. Earth is actually closest to the Sun (perihelion) in early January, during the northern winter.
The physics: Tilt changes how directly sunlight hits the ground and how long the days are. When it's summer in India, it's winter in Australia, at the same distance from the Sun.
Try it at home: Shine a torch straight down onto a table, then at a slant. The slanted light spreads out over a bigger area and is dimmer.
The far side gets just as much sunlight as the near side. It's only permanently hidden from us, because the Moon is tidally locked and spins once per orbit.
The physics: At new Moon, the near side is dark and the far side is fully lit.
Try it at home: Walk slowly in a circle around a friend while always facing them. They see only your front, but you've turned all the way round.
Your cup of tea also follows E = mc². It's just really bad at showing off.
The myth
E = mc² only matters for nuclear bombs and stars.
Myth or fact? Take a guess.
The truth
It applies to all energy changes. Even a chemical reaction or a cup of tea heating up changes mass by a tiny amount. The effect is just far too small to notice except in nuclear reactions.
The physics: In nuclear fission, roughly 0.1% of the mass is converted to energy. In chemical reactions, the fraction is millions of times smaller.
They're not vacuum cleaners. They're just very heavy.
The myth
Black holes suck in everything around them like cosmic vacuum cleaners.
Myth or fact? Take a guess.
The truth
From far away, a black hole's gravity is just like any other object of the same mass. If the Sun turned into a black hole of the same mass, Earth would keep orbiting exactly as before (though it would get very cold).
The physics: Only very close to it, near the event horizon, is gravity strong enough to trap even light.
The electron isn't shy of humans. It reacts to a detector just the same.
The myth
In quantum physics, a conscious observer changes reality just by looking.
Myth or fact? Take a guess.
The truth
"Observation" means a physical interaction that records information (like a detector), not a mind. A detector changes the result just as much as a person would.
The physics: In the double-slit experiment, the interference pattern disappears when something records which slit each particle went through, whether or not any human ever looks at the record.
Great for a school poster. Not great for actual physics.
The myth
Atoms are tiny solar systems, with electrons orbiting the nucleus like planets.
Myth or fact? Take a guess.
The truth
Half true. The Rutherford–Bohr picture is a handy model that explains a lot, such as spectral lines, but electrons don't follow neat orbits. Quantum mechanics describes them as clouds of probability called orbitals.
The physics: Planets can orbit at any distance, but electrons can only have certain energies. And a classically orbiting charge would radiate energy and spiral in, which atoms don't do.
A banana is radioactive. So is your own body. Please don't panic.
The myth
Radioactive things always glow green and only come from labs.
Myth or fact? Take a guess.
The truth
Radioactivity is everywhere and mostly natural. Bananas (potassium-40), granite, brazil nuts, the air (radon) and your own body are all slightly radioactive, and radioactive materials mostly don't glow at all.
The physics: Potassium-40 is a natural isotope in all potassium. A typical adult has about four thousand radioactive decays happening inside them every second.