Your turn
Each lab is one part of the video. Drag, slide and tap, and see what happens.
Each lab isolates one idea. The models are simplified teaching sketches, not real ride data.
Tap the buttons and slide the sliders.
Pick a start. After the top, does the train ever get pushed again?
Compare a chain lift with a magnetic launch. Either way there is one energy input, then the train coasts.
Pick a start and watch the train go!
Drag the train along the track. Watch the energy bar swap height for speed.
Drag the train and watch potential energy become kinetic energy. Try a heavy train: the speed is the same.
Drag the train. Where is it fastest?
No friction in this lab: the ideal model.
Turn up the friction. How far does the train still get?
Raise friction and watch mechanical energy become heat, and the reachable height fall.
Slide it. More rubbing, less far!
A simplified friction model, not real ride data.
Send the train over the hill faster. When do you float?
Change the speed and read the g meter at the dip and the crest.
Make it go faster. Do you float?
Switch between the circle and the teardrop. Which loop pushes you harder?
Compare the peak g of a circular loop and a clothoid of the same height.
Set the hills and the loop. Can your train make it home without a painful loop?
Keep every peak under the energy line after losses, and keep the loop under about 4 g.
Change the hills. Can the train get home?
A teaching model with simple friction.
A roller coaster train has no engine! So how does it zoom so fast?
A chain pulls the train up the first hill. Click, clack, click! That sound is a safety catch. It stops the train from rolling back.
Up high, the train is full of stored energy, like a stretched rubber band. When it rolls down, that energy turns into speed. It goes fastest at the bottom.
The wheels rub on the track, and the air pushes back. That rubbing makes a little heat. So the train has less energy for every hill, and each hill must be a bit lower.
At the bottom of a dip, you feel heavy. At the top of a fast hill, you float! Extra wheels under the track hold the train on.
A roller coaster train almost never has an engine of its own.79 Instead, it gets one big push of energy at the start: a chain hauls it up the first hill, or a launch system fires it along the track. After that, the train simply coasts. Gravity pulls it down each drop, turning height into speed, and every climb turns speed back into height.212
Along the way, friction and air resistance take a small amount of energy out of the ride as heat. That's why each hill is lower than the one before, and why the first hill is the tallest on the whole ride.1012 At the end, brakes take away the last of the speed and the train rolls into the station.9
On most coasters, a long chain runs up the middle of the first hill. Hooks called chain dogs under the train catch the chain, and a motor at the bottom drags the train to the top. Some rides use rows of spinning drive tires or a cable instead.11
That famous click-clack on the way up isn't the chain. It's the anti-rollback device: metal dogs on the train fall into a saw-toothed ratchet beside the track, again and again. If the chain ever stopped or broke, the dogs would catch in the teeth and keep the train from rolling backwards.11 An early version, John Miller's safety chain dog, was patented in 1910.8
Launch coasters skip the hill. They fire the train along a flat track with hydraulic catapults, flywheels, drive tires or electromagnets called linear motors.710 Stealth at Thorpe Park in England goes from 0 to 128 km/h (80 mph) in under two seconds.7 Either way, the idea is the same: put all the energy in at the start.
Hauling a train up a hill is like winding up a spring. The energy is stored in the train's height, ready to be released. Physicists call this gravitational potential energy. The higher the hill, the more energy is stored.12
As the train drops, gravity turns that stored energy into kinetic energy, the energy of motion. At the bottom of the drop, the train is at its fastest. On the next climb, the swap runs backwards: speed turns back into height, and the train slows down.25
potential energy = m·g·h ↔ kinetic energy = ½·m·v²
If there were no friction at all, the total of the two would stay exactly the same at every point on the track. Energy is never created or destroyed, only changed from one kind into another. This is called the conservation of energy.26 The track can push on the train without changing its energy, because it always pushes at right angles to the direction the train is moving. Only gravity speeds it up or slows it down.14
Surprisingly, no. The mass m appears on both sides of the energy equation, so it cancels out. The speed at the bottom depends only on how far the train has dropped (and how fast it was going at the top), not on how heavy it is or the exact shape of the slope.1 In real life, air drag makes a small difference, so this is roughly true rather than exactly.
| Drop height (from rest, no friction) | Speed at the bottom |
|---|---|
| 20 m | about 19.8 m/s = 71 km/h (44 mph)1 |
| 65 m (The Big One, Blackpool) | real ride: about 119 km/h (74 mph)7 |
If energy only swapped between height and speed, a train could swing back up to its starting height forever. Real trains can't. The wheels rub on the rails, and the air pushes against the train. These forces turn a little of the train's energy into heat (and a bit of sound) on every stretch of track.23
That energy isn't destroyed. It has just leaked out of the ride, where the train can't use it again.2 So designers make each hill a little lower than the one before, and the lift hill is always the tallest.1012 Most coaster wheels are made of polyurethane, a tough plastic that rolls smoothly.10 At the end, a brake run removes whatever speed is left, and the train returns to the station.910
Speed itself isn't what makes a coaster thrilling. You go faster on a highway. What you feel is acceleration: changes in your speed or direction.4 The tighter the curve and the faster you go, the bigger the acceleration (a = v²/R).413
At the bottom of a dip, the track has to push you upward to bend your path, so it pushes harder than your normal weight. You feel heavy, pressed into your seat. Riders call these positive g-forces. Your actual weight doesn't change; only the push from the seat does.48 Measurements on big coasters show about 3.5 g at the bottom of the first drop: three and a half times your normal weight.7
Over the top of a fast hill, the opposite happens. The track curves away beneath you and pushes on you less than usual, or not at all. You float off your seat. This is airtime, a moment of zero or "negative" g.712 Your stomach and other organs float a little too, which is the "butterflies" feeling.78 Riders at the front or back of the train get the most airtime over hills, while the middle feels the strongest push in the valleys.7
Each car rides on three kinds of wheels.109
John Miller, the same inventor behind the safety chain dog, is credited with under-friction (up-stop) wheels around 1919. They made steeper drops and faster hills possible.8
Early looping coasters used perfect circles. The Flip-Flap Railway at Coney Island (1895) had a circular loop about 25 feet (8 m) across, and it was uncomfortable and dangerous; riders got whiplash.87
The problem is physics. The train slows down as it climbs the loop, but it still needs enough speed at the top to stay pressed to the track. For a circle, that means entering so fast that riders feel about 6 g at the bottom, then almost nothing at the top.47
Modern loops are shaped like an upside-down teardrop, called a clothoid. The curve is wide and gentle at the bottom, where the train is fast, and tight at the top, where it's slow.47 The gentle bottom keeps the push to about 3.5 to 4 g, and the tight top keeps the slower train pressed to the track.47
| Loop, 30 m tall (our model) | Entry speed needed | Strongest push |
|---|---|---|
| Circle | about 99 km/h | about 6 g |
| Teardrop (clothoid) | about 93 km/h | about 3.5–4 g |
These numbers come from a simple energy model with no friction, the same one the interactive uses; they match the measured values quoted above.47
Wooden coasters are usually shorter, slower and non-looping, but they sway and rattle, which is part of their charm. Tubular steel track can be bent into loops and corkscrews, and it allows taller, steeper hills and faster speeds.912
The ancestors of coasters were the "Russian Mountains": 17th-century ice slides near St Petersburg, 70 to 80 feet tall.108 The first gravity coaster in the United States was LaMarcus Thompson's Switchback Railway at Coney Island in 1884. It was 600 feet (183 m) long and ran at about 6 mph.810 Kingda Ka in New Jersey, 456 feet (139 m) tall, held the height record from 2005. Falcon's Flight in Saudi Arabia, which opened in December 2025 with a 640-foot (about 200 m) drop, is now listed as the tallest, fastest and longest coaster.10
The same pull that runs every coaster is explained in How does gravity work?. Launch coasters borrow ideas from how rockets work, and the pushes you feel on a coaster are cousins of the forces in how planes fly.
Almost never on the train itself. A chain lift or a launch system gives the train one big dose of energy at the start. After that, gravity does the work for the rest of the ride and the train simply coasts.
Each car has three sets of wheels: road wheels on top of the rail, side-friction wheels on the side, and up-stop wheels tucked underneath. The up-stop wheels lock the train onto the rail, so it can't lift off even when riders float over a hill.
Over the top of a fast hill the track drops away and pushes on you less than usual, so you feel light or even float (airtime). Your internal organs float a little too, which is the butterflies feeling.
The first hill gives the train all the energy it will ever have. Friction and air resistance turn a little of that energy into heat on every stretch, so each later hill has to be lower for the train to get over it.
Not really. In physics, mass cancels out: the speed at the bottom of a drop depends on the height of the drop, not the weight. A 20 meter drop gives about 71 km/h (44 mph) whether the train is full or empty. Air drag makes small real-world differences.
To get over the top of a circular loop, the train must enter so fast that riders feel about 6 g at the bottom. Modern loops are teardrop-shaped (clothoid): wide at the bottom, tight at the top, which keeps forces to about 3.5 to 4 g.
It's the anti-rollback device, not the chain. Metal dogs under the train drop into a saw-toothed ratchet along the lift hill, so if the chain stopped or broke, the train couldn't roll backwards.