Physics and motion

50 to explore · page 1 of 2

• Watch Try it What If? Lab What if gravity disappeared? Gravity is the pull that makes a dropped ball fall and keeps your feet on the ground. Switch it off in our model and watch what a ball does instead, then find out why astronauts float.
• Watch Try it What If? Lab What if water were denser? Water pushes up on anything you put in it. A heavier, denser liquid pushes up harder. In our model, a block that sinks in water floats in a pretend liquid twice as dense, with only 60 percent of it under the surface.
• Watch Try it What If? Lab What if wheels were square? A square wheel on a flat road lifts its axle up and down with every corner. In our model it bounces almost 9 centimeters and loses most of its motion at each bump. On a road of curved humps, though, the same square rolls perfectly smoothly.
• Watch What If? Lab What if every surface were slippery? Friction is the grip between surfaces. It lets you walk, hold a pencil and stop a bike. Imagine a world where every surface was as slippery as ice, and follow what would happen to walking, writing and driving.
• Watch What If? Lab What if there were no springs? A spring stores energy when you squash or stretch it, then gives it back as it springs into shape. Imagine a world with no metal springs at all, and follow what would happen to bouncy beds, clicky pens, old-style clocks and car rides.
• Watch What If? Lab What if you played catch on a merry-go-round? Roll a ball straight across a spinning merry-go-round and, to the riders, it seems to curve away. Someone standing on the ground sees it go straight. The same trick, on our spinning Earth, bends winds and makes big storms swirl.
• Watch What If? Lab What if gravity pulled sideways? “Down” is simply the direction gravity pulls: toward the center of Earth. Imagine gravity pulling sideways instead, and follow what would happen to walking, to rivers, and to the very meaning of up and down.
• Watch What If? Lab What if you could see sound? Sound is a wave of squeezed and stretched air that our ears can feel but our eyes can't see. Imagine seeing it, then meet the real tools, like spectrograms and special cameras, that scientists use to turn sound and moving air into pictures.
• Watch What If? Lab What if time slowed down when you moved fast? This what-if is real. Einstein's relativity says a moving clock ticks slightly slower, and scientists have measured it with atomic clocks, fast particles and GPS satellites. Explore how big the effect is, why we never notice it, and why your phone's map depends on correcting it.
• Watch What If? Lab What if air had no weight? The air above you has weight, and that weight presses on everything at about 101,000 newtons on every square meter at sea level. That pressing pushes juice up a straw and holds a suction cup on a window. Imagine air with no weight and follow what would stop working.
• Watch Try it What If? Lab What if a ball were thrown sideways off a tower? Drop one ball from a 20-meter tower and throw another straight out sideways at the same moment. The thrown ball travels about 10 meters away, yet in our model both land at the same moment, about 2 seconds later: moving sideways does not change how fast a ball falls.
• Watch Try it What If? Lab What if a ball were thrown twice as fast? In our model, a ball launched at 10 meters per second, aimed at 45°, lands about 10 meters away. Launch it twice as fast, at 20 meters per second, and it lands about 41 meters away: four times as far, not twice. Speed helps twice over, making the ball fly farther sideways and stay up longer.
• Watch Try it What If? Lab What if a bowling ball hit a ping-pong ball? In our model, a heavy puck 100 times the mass of a light one stands in for a bowling ball hitting a ping-pong ball. Moving at 2 meters per second, the heavy puck hardly slows down at all, to about 1.96, while the light puck shoots off at about 3.96 meters per second: nearly twice the heavy one's starting speed.
• Watch Try it What If? Lab What if a bridge had no supports? A beam bridge stays up because its supports push up on it. In our model, a steel beam held at both ends barely bends under a 20-tonne truck. Hold it at one end only and it bends about eight times as much. Take away every support and nothing holds it up at all.
• Watch Try it What If? Lab What if a heavier box slid down a ramp? You might guess that a heavy box would slide down a ramp faster than a light one. In our model, a 5-kilogram box on a wooden ramp tilted at 40° speeds up by about 4.1 meters per second every second. Make it 50 kilograms, ten times heavier, and it slides in exactly the same way.
• Watch Try it What If? Lab What if a magnet were farther away? A magnet's pull fades astonishingly fast. In our model, a neodymium magnet yanks a paperclip in from 5 centimeters away. Move the clip to 10 centimeters, just twice as far, and the magnetic field is one eighth as strong, but the pull on the clip is 128 times weaker, far too weak to slide it across the table.
• Watch Try it What If? Lab What if a pendulum swung very high? Small pendulum swings all take almost exactly the same time, which is why pendulums made such good clocks. But pull one back to 150° and each swing takes about three quarters longer. Find out why in Olly's lab, and why clockmakers kept their swings small.
• Watch Try it What If? Lab What if a ramp were covered in rubber? Some surfaces grip and some hardly grip at all. In our model, a block on an icy ramp tilted at 15° slides off and glides about 31 meters across the icy floor. Cover the same ramp in rubber and the block does not move at all. Rubber can hold it still until the ramp is tilted all the way to 45°.
• Watch Try it What If? Lab What if a skydiver spread out like a starfish? Air pushes up on anything falling through it, and the push grows as the faller speeds up. In our model, an 80-kilogram skydiver curled up small has a top speed of about 72 meters per second. Spread out like a starfish, catching nearly three times as much air, the top speed drops to about 43 meters per second.
• Watch Try it What If? Lab What if a slide were steeper? On a slope, part of gravity's pull points down the slope, and the steeper the slope, the bigger that part. In our model, a wooden block on a 4-meter wooden ramp tilted at 30° reaches the bottom in about 1.8 seconds at about 4.3 meters per second. Tilt it to 45° and it takes only about 1.3 seconds and arrives at about 6.2 meters per second.
• Watch Try it What If? Lab What if a swing had a heavier rider? You might think a heavier rider would make a swing go faster, or slower. In our model, a swing with 2-meter ropes takes about 2.9 seconds to swing over and back whether the rider weighs 1 kilogram or 20. A pendulum's swing time depends on its length and on gravity, not on how heavy it is.
• Watch Try it What If? Lab What if a swing had much longer ropes? A swing is a kind of pendulum, and its rope length sets how quickly it goes back and forth. In our model, a swing 1 meter long takes about 2 seconds to swing over and back. Make the ropes four times longer, 4 meters, and each swing takes about 4 seconds: twice as long.
• Watch Try it What If? Lab What if a swing never slowed down? A real swing slowly dies down because air and friction take away a little of its energy on every swing. In our model, with a little air and friction, a swing pulled back 20° is down to about 13° after six swings. Switch them off, a simplification only a model can make, and it keeps swinging 20° every time.
• Watch Try it What If? Lab What if a table were very grippy? A magnet only slides a paperclip toward it when its pull beats the grip of the table. Make the table four and a half times grippier and the clip 6 cm away stays put. But the magnet's reach shrinks by only about a fifth. Find out why.
• Watch Try it What If? Lab What if a truck stopped near the end of a bridge? A beam bridge bends most when a truck sits in the middle. Stop the same 20-tonne truck near one end, 10 percent of the way across, and in our model the steel beam sags less than a third as much and works only about a third as hard. Find out why the end of a bridge has it easier.
• Watch Try it What If? Lab What if a wing tilted too far? Tilting a wing up into the wind makes more lift, but only up to a point. In our model, a small plane's wing tilted at 14° makes about 43 kilonewtons of lift at 60 meters per second. Tilt it to 20° and the air breaks away from the top of the wing: the wing stalls and lift drops to about 35 kilonewtons. At slow speeds, that drop can mean too little lift to stay up.
• Watch Try it What If? Lab What if balls did not bounce? In our model, a moving puck hits an identical puck that is standing still. If they are perfectly bouncy, the first one stops dead and the second shoots off at the same speed. If they cannot bounce at all, they stick together and roll on at half the speed, and half of the movement energy turns into heat and sound.
• Watch Try it What If? Lab What if gravity doubled? Gravity makes a dropped ball speed up as it falls. Make the pull twice as strong in our model and the ball speeds up twice as fast, so it lands sooner and hits the ground harder. But it does not land in half the time. Find out why.
• Watch What If? Lab What if heat flowed from cold to hot? Drop an ice cube into hot tea and the tea cools while the ice melts: heat moves from hot to cold, all by itself. It never flows the other way on its own. Fridges and heat pumps can move heat from cold to hot, but only by using energy. Imagine a world where heat flowed backward.
• Watch What If? Lab What if light had only one color? White sunlight is secretly a mixture of every color, from red to violet. Raindrops and glass prisms spread it out into a rainbow. Imagine light that had only one color: there might be no rainbows, and the world might look like one color in different shades.
• Watch Try it What If? Lab What if light reflected differently? Light leaving water bends as it crosses into air, and a little of it bounces back. Tilt the beam past about 49 degrees and something remarkable happens: no light gets out at all. Every bit reflects back inside, the trick that keeps light inside optical fibers.
• Watch What If? Lab What if light traveled as slowly as a bicycle? Light zips along at almost 300,000 kilometers every second, so fast that seeing seems instant. But it isn't: you always see things slightly in the past. In 1999, scientists slowed light to about 17 meters per second, the speed of a sprinting cyclist. Imagine a world where light always moved that slowly.
• Watch Try it What If? Lab What if magnets became stronger? A magnet's pull fades very fast as you move away. In our model, a ceramic magnet can't budge a paperclip 5 centimeters away, but a magnet three times stronger pulls it right in. Yet its reach grows by much less than its strength.
• Watch What If? Lab What if mirrors did not exist? A mirror is a very smooth, shiny surface that bounces light back neatly, so it makes a clear picture of you. Mirrors also gather starlight in giant telescopes and help people see around corners with periscopes. Imagine a world with no mirrors and follow what might change.
• Watch What If? Lab What if nothing could bounce? A ball bounces because it squashes when it hits the ground and then springs back, giving back the energy it stored. Springs store energy in the same way, and sound bounces off walls as echoes. Imagine a world where nothing could spring back, and follow what might change for games, sounds and springs.
• Watch Try it What If? Lab What if objects had different masses? When two equal pucks hit head-on, the first one stops and the second one zooms away. Make the second puck ten times heavier and everything changes: the light puck bounces back and the heavy one only creeps forward.
• Watch What If? Lab What if shadows had colors? A shadow is a place where an object blocks the light. With one lamp, the shadow looks dark. But shine a red and a green light on one object and you get two shadows, one green and one red, because each shadow is lit by the light that is not blocked. Add a blue light and the shadows turn yellow, cyan and magenta.
• Watch Try it What If? Lab What if sound couldn’t travel through air? Sound is a push passed from particle to particle. In air it travels about 343 meters every second. Take the air away, as in empty space, and there is nothing to pass the push along, so a clap makes no sound at all. Water and steel still carry it, and much faster.
• Watch Try it What If? Lab What if the second hill were taller than the first? A roller coaster gets all its energy from its first big hill, and friction slowly uses some up along the way. In our model, a car that starts 40 meters up easily gets over a 25-meter second hill. Make that hill 45 meters, taller than the start, and the car can never reach the top: it rolls back.
• Watch Try it What If? Lab What if there were no air resistance? Air pushes back on anything falling through it, and light, spread-out things like paper feel that push the most. Switch the air off in our model and a light paper cup drops as fast as a stone, landing in under a third of the time.
• Watch What If? Lab What if there were no echoes? An echo is sound that bounces back to you. Bats and dolphins send out sounds and listen for the echoes to find food, and ships use echoes to measure how deep the sea is. Imagine a world with no echoes and follow what might change for animals and people.
• Watch Try it What If? Lab What if there were no friction? Friction is the grip between two surfaces. It slows a wooden block sliding down a ramp and stops it on the floor. Switch friction off in our model and the block races down faster and then slides along the floor forever.
• Watch What If? Lab What if there were no magnets? You can see magnets holding pictures on a fridge, but most magnets are hidden. They sit inside electric motors, speakers and the generators that make electricity, and a compass needle is a magnet too. Imagine a world with no magnets and follow what might stop working.
• Watch Try it What If? Lab What if two pucks hit off-center? When a sliding puck hits an identical still puck straight on, it stops dead and the other one shoots away. Hit it off-center and both slide off, at a right angle to each other. Find out why, and why pool players know this trick.
• Watch What If? Lab What if you could run at the speed of sound? Sound zips through air at about 343 meters per second, more than 30 times faster than the fastest human sprint. Anything that goes faster than sound pushes the air into a shock wave that people hear as a sonic boom. Imagine running that fast, then meet the jets that really do it.
• Watch What If? Lab What if you could shrink to the size of an ant? Small creatures live in a strange world. For a tiny ant, the air keeps a fall slow, a drop of water might look as big as a beach ball, and its neck turns out to be very strong for its size. Imagine shrinking to ant size and explore each of these, one careful step at a time.
• Watch Try it What If? Lab What if you dropped a ball from four times higher? A ball dropped from 10 meters lands in about 1.4 seconds. Drop it from 40 meters, four times as high, and you might expect four times as long. In our model it takes only about 2.9 seconds: just twice as long, because a falling ball keeps speeding up.
• Watch Try it What If? Lab What if you threw a ball at a lower angle? Throw a ball at 15 meters per second, aimed halfway between flat and straight up (45°), and in our model it lands about 23 meters away. Aim much flatter, at 15°, and it lands only about 11 meters away, in less than a second. Without air, 45° sends a ball farthest on flat ground.