Experiments you can run

149 to explore · page 1 of 4

• 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 balloon floated very high? As a balloon floats higher, the air around it gets thinner and pushes on it less, so the gas inside spreads out and the balloon swells. In our model, a perfectly stretchy balloon launched at sea level is about 14 times its starting size by the time it reaches 20 kilometers.
• Watch Try it What If? Lab What if a battery had more voltage? A battery's voltage is how hard it pushes electric current around a circuit. Swap a 3-volt battery for a 9-volt one in our model and the same two bulbs carry three times the current, and each one uses nine times the power. Find out why, and why a real bulb can burn out on too much voltage.
• Watch Try it What If? Lab What if a battery wasted energy as heat? A battery's label tells you how much energy it stores. But on the way from the battery to a device, some energy always turns into heat in the wires and electronics. In our model, a 60-watt-hour battery runs a 10-watt lamp for 6 hours when nothing is lost. If 30% is lost as heat, the lamp goes dark after 4 hours 12 minutes.
• Watch Try it What If? Lab What if a battery were old and tired? Every battery has a little resistance inside it. A fresh battery has hardly any, but as a battery gets worn out, that inside resistance grows. In our model, four bulbs side by side glow at full brightness on a fresh 3-volt battery. Make the battery old and tired, and watch what happens to the bulbs and to the battery itself.
• Watch Try it What If? Lab What if a beach lost its dune plants? Grasses such as marram grass and sea oats grow on sand dunes, and their spreading roots help hold the sand in place. In our coast model, taking away all the plant cover makes ordinary waves wear a sandy shore about 1.7 times faster.
• Watch Try it What If? Lab What if a beam stood on its edge? The same steel beam can lie flat or stand on its edge. It weighs exactly the same either way, yet in our model the tall way sags only a quarter as much under a truck. Find out why a beam's height matters far more than its width.
• Watch Try it What If? Lab What if a boat carried too much cargo? A steel boat floats because its hollow shape pushes aside lots of water. Every kilogram of cargo pushes it a little deeper. Load Olly's model boat step by step, find the most it can carry, then see what happens with 400 kilograms on board.
• Watch Try it What If? Lab What if a boat changed shape? Drop a solid block of steel in water and it sinks straight down. Shape steel into a hollow boat hull and it floats. In our model, a steel hull the same outside size as the block bobs on the water with about a third of it showing, and can even carry cargo. Find out how shape, not just material, decides whether something floats.
• 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 bridge weighed nothing? A long bridge carries more than traffic: it also has to hold up its own heavy body. In Olly's model, switch off a 60-meter steel beam's weight and see how much of its strength was being used just to hold itself up.
• Watch Try it What If? Lab What if a bridge were built with different materials? Steel, wood and aluminum all behave differently when a heavy truck rolls onto them. In our model, a wooden beam the same size as a steel one bends about five times as much under the same truck, yet it still holds, partly because wood is so much lighter. Find out why bending and breaking are two different things.
• Watch Try it What If? Lab What if a bridge were held up at one end only? A beam held at only one end, like a diving board, is called a cantilever. In this lab a 10-meter steel beam carries a 20-tonne truck. Take away one support and watch how much more it bends, and find where the beam works hardest.
• Watch Try it What If? Lab What if a bridge were twice as long? A steel beam bridge 20 meters long sags about 14 millimeters under a 20-tonne truck. Make it twice as long and the sag does not just double: in our model it grows almost 14 times. Find out why long bridges need different designs.
• Watch Try it What If? Lab What if a coast were made of hard rock? Waves wear coasts away, but not every coast wears at the same speed. In our model, a bare sandy island facing ordinary waves keeps about 72 percent of its land after 50 model years. Make the same island of hard rock and it keeps about 99 percent. That is why hard rock is often left sticking out to sea as headlands.
• Watch Try it What If? Lab What if a crane used more pulleys? Lifting a 100-kilogram crate straight up on one rope is hard work. In this lab, add pulleys so that more pieces of rope hold the load. Watch how the pull you need gets smaller, and how much more rope you have to pull.
• Watch Try it What If? Lab What if a glider had short, stubby wings? A glider flies with no engine, so it needs wings that work as well as possible. Squash a glider's long, thin wings into short, stubby ones with the same area, and see what happens to its lift in Olly's model.
• Watch Try it What If? Lab What if a greenhouse got too hot? Plants grow best when it is warm, but not too warm. Heat up a model leaf from a comfortable 25 °C to a scorching 45 °C and watch two things change at once: the leaf makes sugar more slowly, and it burns sugar faster. At some point it burns more than it makes.
• Watch Try it What If? Lab What if a habitat lost its water supply? Water makes plants grow, and plants feed animals. In our model, a dry spell cuts the plant food from 50 tonnes a year to 20, so the land can feed far fewer deer. Watch the herd shrink to fit, then find out how drought affects real wildlife and how people help.
• 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 home ran on a big battery? A big home battery in our model stores 13,500 watt hours. Running a small 500-watt load, it lasts more than a day; switch on a 2,000-watt heater and it is empty in under seven hours. The secret is dividing the energy stored by how fast it is used.
• Watch Try it What If? Lab What if a house had a tiny heater? A warm house is always leaking heat into the cold outside. A heater keeps it warm only if it can put heat back as fast as it leaks out. In our model, a 10-kilowatt heater keeps a leaky house at 20 °C on a freezing day. Swap it for a tiny 3-kilowatt heater, and the house slowly cools until it finds a new balance.
• Watch Try it What If? Lab What if a house had no insulation? Heat always leaks out of a warm house into the cold outside. Insulation in the walls and roof slows that leak down. In our model, an insulated house on a freezing day needs its heater only about a third of the time. Take the insulation away and the same heater runs nonstop, and the house still cools to about 17 °C.
• Watch Try it What If? Lab What if a house were built on soft clay? A building presses down on the ground under its foundation. Sand, gravel and rock can each safely carry a different amount. In this lab, a 300-tonne building stands safely on sand. Move it onto soft clay without changing anything else, and see what happens and how to fix it.
• Watch Try it What If? Lab What if a house’s heating switched off on a cold night? A warm house is always leaking heat into the cold night. If the heating stops, nothing replaces it. In our model, an insulated house at 20 °C on a 0 °C night cools to about 15 °C in 12 hours, and then more and more slowly as it gets closer to the outside temperature.
• 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 clock went to the Moon? A pendulum clock keeps time by counting swings, and gravity sets how fast each swing goes. In our model, a 1-meter pendulum takes about 2 seconds per swing on Earth but almost 5 seconds on the Moon, so a clock set up on Earth would show only about 24 minutes for every real hour.
• 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 plane flew on Mars? A wing makes lift by pushing air down, so the thickness of the air matters a lot. In our model, a small plane at 60 meters per second makes about one and a half times its weight in lift on Earth. In Mars's thin air, the same plane makes only about 2 percent of what it needs.
• Watch Try it What If? Lab What if a plane had different wings? A plane's wings push air down, and the air pushes the wings up. That push is called lift. In our model, a small plane cruising at 60 meters per second has plenty of lift. Cut its wing area about in half and the lift drops by about half too, not enough to hold the plane up, unless it flies much faster.
• Watch Try it What If? Lab What if a plant lived in a dark cave? A green leaf makes sugar from light, water and air, but it also uses up a little sugar all the time just to stay alive. Carry our model leaf from bright sunshine into a dim cave and watch what happens when the sugar it makes drops below the sugar it uses.
• 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 rocket carried less fuel? Most of a rocket is fuel. In our model, a rocket that is 85 percent fuel gains about 5.7 kilometers per second. Cut the fuel to half the rocket and it gains only about 2.1, less than half as much speed. Find out why rockets need so much fuel, and why they drop parts on the way up.
• Watch Try it What If? Lab What if a roller coaster had greater friction? Once a roller coaster is let go at the top of its first big hill, gravity does the rest: all its energy comes from that hill. Friction from the wheels and the air slowly uses that energy up. In our model, a coaster with smooth wheels finishes the whole ride. Make the friction four times bigger and it slows down so much that it can't get over the second hill and rolls back.
• Watch Try it What If? Lab What if a roller coaster were launched? A roller coaster gets its energy from height, but some get it from a fast launch instead. In this lab, a car on a small 15-meter hill can't make a loop. Give it a 10-meter-per-second launch and see if that extra speed carries it all the way around.
• Watch Try it What If? Lab What if a roller-coaster loop were bigger? A coaster car needs enough speed at the top of a loop to stay pressed against the track. In this lab, the car starts at 40 meters and easily makes a 10-meter loop. Double the loop to 20 meters and see what happens, then find how tall the first hill must be.
• 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 solar panel lay flat? Sunlight gives a panel the most energy when it hits the panel straight on. In London in March, the Sun stays low in the sky, so our model panel tilted at 40° makes about 1.86 kilowatt-hours in a day. Lay it flat and the slanting light spreads out: it makes only about 1.17.
• Watch Try it What If? Lab What if a spacecraft traveled faster? A rocket's top speed depends on how fast its hot exhaust gas shoots out and on how much of the rocket is fuel. In our model, switching from a kerosene engine to a faster hydrogen engine lets the same rocket gain nearly half as much speed again.
• 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 switch were left open? A switch is a little gate in a circuit. Closed, it lets electric current flow all the way around the loop. Open it in our model and the loop has a gap: the current drops to zero and every bulb goes dark at once, however the bulbs are wired.
• 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.