Every What If? Lab

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• 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 What If? Lab What if a solar eclipse lasted all day? During a total solar eclipse, the Moon's shadow races across Earth at more than 2,400 kilometers per hour, so the Sun stays fully covered for only a few minutes in any one place. In April 2024, the longest was 4 minutes and 28 seconds. Find out why eclipses are so short, how animals react to the sudden dusk, and imagine one that never ended.
• 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 What If? Lab What if a town used up its groundwater? Below the ground, water fills the tiny gaps between grains of rock and sand. In the United States, this groundwater is the drinking water for about half of all people. Rain and snow refill it, but often slowly. Imagine a town pumping faster than nature refills it, and follow what might change and how people help.
• 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 turbine caught every bit of the wind? A wind turbine slows the wind down to take some of its energy. So why not slow it all the way down and take all of it? In our model, a good turbine catches 45% of the wind's power. Push it to the very best any turbine could ever do, and you hit a wall at about 59%, called the Betz limit.
• Watch Try it What If? Lab What if a turbine had a small generator? A wind turbine's blades catch the wind, but its generator turns that spin into electricity, and every generator has a top limit called its rated power. In our model, big blades in a strong wind make about 2.13 megawatts with a large generator. Swap in a 1-megawatt generator, and the turbine can never make more than 1 megawatt, however hard the wind blows.
• Watch Try it What If? Lab What if a wind turbine had different blades? A wind turbine's blades sweep out a big circle, catching the wind that blows through it. Make the blades twice as long and the circle holds four times as much wind. In our model, that turns about 1.2 megawatts of electricity into about 4.9 megawatts, in the same wind. Find out why wind turbines keep getting bigger.
• 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 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 What If? Lab What if all flowers were the same color? Flower colors are signals. Bees go for blue and yellow, hummingbirds for red, and night-flying moths for white. Imagine a world where every flower was the same color: how would pollinators find the right flowers, and what might happen to the plants?
• Watch Try it What If? Lab What if all the sea ice melted? Sea ice floats, so it is already pushing aside about as much water as it will make when it melts, like an ice cube in a glass. In our model, melting all the Arctic's springtime sea ice raises the sea by only about 2 millimeters. The same ice melting on land would raise it about 7 centimeters.
• Watch What If? Lab What if all trees disappeared? Trees take in carbon dioxide and store carbon in their wood, put water into the air, hold soil in place and give homes to most kinds of land animals. Follow what would happen without them, and find out why the ocean still makes about half of our oxygen.
• Watch What If? Lab What if an asteroid struck the Moon? The Moon's craters are a record of space rocks landing over billions of years, and small ones still land there every day. Scientists watch for tiny flashes of light on the Moon and later find the brand-new craters. Explore what happens when a rock hits the Moon, and why the Moon keeps going around Earth as always.
• Watch Try it What If? Lab What if an electric plane carried more batteries? An electric plane needs batteries to fly, and more batteries could store more energy. But batteries are heavy. In our model, a small plane weighing 1,100 kg flies at 55 meters per second with lift to spare. Load it up to 1,500 kg and, at the same speed and wing tilt, its wings make only 88 percent of the lift it needs.
• Watch What If? Lab What if an ice age came back? About 20,000 years ago, ice sheets more than 3,000 meters thick covered much of North America, and the sea was about 125 meters lower than today. Ice ages come and go over tens of thousands of years as Earth's orbit and tilt slowly change. Imagine an ice age returning, and follow what might change.
• Watch What If? Lab What if an invasive species entered an ecosystem? An invasive species is a living thing that ends up somewhere it doesn't naturally live and causes harm there. In this thought experiment, follow two real stories from Australia: cane toads, brought to eat beetles in sugar cane fields in 1935, and rabbits, which probably spread mostly from 24 brought in 1859. Then find out how people try to keep ecosystems in balance.
• Watch Try it What If? Lab What if an island experienced more erosion? Wave power grows with the square of wave height, so a wave about three times taller carries about 11 times the power. In our model, swapping 1.5-meter waves for 5-meter storm waves makes a sandy island wear away about 11 times faster, though plant roots help hold it together.
• Watch Try it What If? Lab What if an ocean food web changed? Antarctic krill are small shrimp-like animals, but they feed a huge number of bigger ones. Take krill out of our model's Southern Ocean food web and all seven other species are affected: every animal in it loses all its food, from silverfish to orcas.
• Watch Try it What If? Lab What if animal populations grew beyond available food? Land can only feed so many animals. In our model, a herd of deer grows until it nears that number. But what if the deer react to crowding late? Watch the herd shoot past what the food can feed, then fall back, and meet real herds that did the same.
• Watch What If? Lab What if animals could change color like an octopus? Octopuses and cuttlefish change the color and texture of their skin in the blink of an eye, using thousands of tiny color cells. They use it to hide and to send signals. Imagine if many more animals could do it: who would hide better, what would they say with color, and what would it cost them?
• Watch What If? Lab What if animals did not hibernate? Winter brings two big problems for animals: less food and lots of cold. Bats, groundhogs, dormice and bears get through it by slowing their bodies right down. Imagine they couldn't, and follow what might change for finding food, saving energy and the famous winter sleepers.
• Watch What If? Lab What if ants left no trails? Many ants mark the way to food with a scent trail, and their nestmates follow it. Because old scent fades, the colony often ends up on the shortest path. Computer scientists even copy the trick. Imagine ants that left no trails and follow what might change.
• Watch What If? Lab What if apples never turned brown? When an apple is cut, a natural chemical in it mixes with oxygen from the air, and the fruit turns brown. Lemon juice and the fridge slow it down, and some apples are now grown to brown less. Imagine apples that never browned and follow what might change.
• Watch What If? Lab What if auroras could be seen everywhere? Auroras glow when tiny particles from the Sun crash into the air high above Earth. Earth's magnetic field steers them toward the poles, so that is where auroras shine most. Imagine lights over the whole planet, find out what makes the colors, and see how people keep satellites safe in big solar storms.
• 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 batteries stored less energy? A battery stores a set amount of energy, and a device uses it up at a steady rate. In our model, a 60 watt-hour battery runs a 10-watt lamp for 6 hours. Shrink the battery to 15 watt hours and the same lamp goes dark after an hour and a half.
• Watch Try it What If? Lab What if beavers built no dams? Beavers eat willow and aspen, and they also build dams that turn streams into ponds. Take the beaver out of our forest food web and the model finds only one change. Then find out why scientists call beavers nature's engineers, and what a food web leaves out.
• Watch Try it What If? Lab What if bees disappeared? Many fruits and vegetables only grow well when bees and other animals carry pollen between their flowers. In our model farm, turn the pollinators down to zero and watch which harvests shrink, which hardly change, and why wheat, rice and corn don't mind. Then meet the people helping pollinators.
• Watch What If? Lab What if birds forgot how to build nests? Nests keep eggs and chicks safe from predators and the weather, and birds build them in amazing ways: from twigs, grass, mud, hair and even spider silk. Imagine every bird forgetting how to build one. Then meet the birds that already manage without, from cliff-ledge murres to emperor penguins.
• Watch What If? Lab What if bridges could float? Most bridges rest on piers that reach down to solid ground. But some bridges really float, held up by huge hollow concrete boxes called pontoons. Find out why engineers float a bridge, how heavy concrete can float at all, and what wind and waves do to a road on the water.
• Watch What If? Lab What if bubbles could last forever? A soap bubble's skin is a thin sandwich of soap and water, and it pops when the water drains or dries away. Scientists in France made a bubble that lasted 465 days. Imagine bubbles that lasted forever and follow the clues: thin films, drying out and frozen bubbles.
• Watch Try it What If? Lab What if buildings had different foundations? A building's whole weight presses down through its foundation onto the ground. A wide foundation spreads that weight out, like snowshoes on snow. In our model, a 200-tonne building on sand is safe on a 40-square-meter footing. Shrink the footing to 8 square meters and it presses five times harder, more than the sand can take, so the building would sink and could crack or tilt.
• Watch Try it What If? Lab What if bulbs were wired side by side? When two bulbs share one loop of wire, they share the battery's push and both glow dimly. Wire them side by side instead, each on its own path to the battery, and each gets the battery's full push. In our model, each bulb then glows four times as brightly. But there's a catch: the battery has to work four times as hard.
• Watch What If? Lab What if cakes had no baking powder? Look closely at a slice of cake and you'll see it is full of tiny holes. Baking powder makes bubbles of a gas called carbon dioxide, and those bubbles puff up the batter as it bakes. Imagine baking with no baking powder and follow what might happen.
• Watch What If? Lab What if canals had no locks? Canals let boats cross land, but land goes up and down while water wants to stay level. Locks solve this: they are like water-filled stairs that lift and lower boats one step at a time. Explore how locks work, what a canal without them can and cannot do, and the giant locks of the Panama Canal.
• Watch What If? Lab What if cars drove themselves? Self-driving cars use cameras, radar, lidar and maps, plus computers that decide when to steer, speed up and brake. Today most cars can only help a human driver, and cars that drive themselves work only in certain places. Explore how these cars see, how they decide, and what sharing the street with them could mean.
• Watch What If? Lab What if cats had no whiskers? A cat's whiskers are not just for looks. They are touch sensors that feel air moving, things brushing past, and the edges of gaps. Imagine a cat with no whiskers: how would it find its way in the dark or know if it fits through a hole?