Every What If? Lab

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• 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 What If? Lab What if a cactus grew in a rainforest? Desert cacti are built to save every drop of water. A rainforest gets rain almost all year. Move a desert cactus into the rainforest and its water-saving tricks could turn into trouble, because soggy soil can make its roots rot. Yet some cacti really do live in rainforests, high up in the trees!
• Watch What If? Lab What if a caterpillar never became a butterfly? A caterpillar is an eating machine. Inside its chrysalis it rebuilds its whole body into a butterfly that can fly, find a mate and lay eggs. Imagine a caterpillar that never changed: what would it miss, and what would happen to the next generation?
• Watch What If? Lab What if a city had no trees? Cities are full of roads, roofs and parking lots that soak up the Sun's heat. Street trees shade them, cool the air, catch rain and give birds a home. Imagine a city with every tree gone: hotter streets, more rain rushing down the drains and fewer birds. Then see how people plant trees to help.
• 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 What If? Lab What if a comet passed close to Earth? Comets are icy leftovers from when our solar system formed. Near the Sun, they warm up and grow a glowing cloud and long tails. Dust they leave behind gives us meteor showers. Astronomers have predicted comets' returns for centuries: Halley's Comet is due back in 2061.
• 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 What If? Lab What if a day lasted 48 hours? Earth spins once about every 24 hours, and almost every living thing has a body clock tuned to that day. Imagine a day twice as long: long, bright days and long, dark nights. What would happen to your sleep, to plants and to animals?
• Watch What If? Lab What if a drought lasted for years? A drought is a long stretch with much less rain or snow than normal, long enough that water runs short. Droughts can last a few weeks, a few months or several years. Imagine a land where the dry years keep coming, and follow its rivers, the ways people save water, and what it takes for a drought to end.
• Watch What If? Lab What if a forest grew back after a fire? In 1988, fires passed through about a third of Yellowstone National Park. Today, the young trees that sprouted afterward have grown into new forests. Follow the forest's comeback: the first plants, the pine cones that open with heat, and the animals that return.
• 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 What If? Lab What if a machine could run forever? For more than a thousand years, inventors have drawn wheels and gadgets that were meant to keep turning forever with nothing to power them. None has ever worked. Follow the energy in this thought experiment to see why: energy is never made from nothing, and every moving machine leaks a little of it away as heat.
• 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 What If? Lab What if a mountain wore away? Even the tallest mountains are slowly broken apart by ice, rain, plant roots and wind, and the pieces are carried away by rivers and glaciers. Imagine following a mountain as it wears away: its rock might end up as sand on a beach, mud on a farm or new land at a river's mouth, while moving plates push other mountains up.
• 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 What If? Lab What if a rainforest had little rain? Rainforests are tall, green forests that get a great deal of rain. In 2005 and 2010, big droughts hit the Amazon rainforest, and satellites watched what happened to its trees. Use those real events to imagine a rainforest with little rain: drier leaves, hungry animals and a forest that might change.
• 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 What If? Lab What if a river changed its course? A winding river wears away the outside of each bend and piles sand on the inside, so slowly, year by year, it moves. Sometimes it cuts off a loop and leaves a lake behind. Imagine a big river changing its course: what would happen to the old loops, and to the towns and bridges beside it?
• Watch What If? Lab What if a river flooded every year? For thousands of years, the Nile in Egypt flooded every year, spreading fresh mud across its banks. That mud made the land rich for farming, in the middle of a desert. Imagine a river that flooded every year: you could plan for it, farm on it, and build banks called levees to control it. Many of the earliest towns grew up beside rivers like this.
• Watch What If? Lab What if a robot had only one sensor? A sensor is a part that lets a robot notice something: light, a bump, a sound. Most robots use several kinds. In this thought experiment, imagine a robot with only a camera, and then one with only touch. What might each one miss? Then see how NASA's Perseverance rover combines many cameras and other sensors to explore Mars.
• 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.