A roller coaster is an energy bank.

Same energy, different outfits.

Energy is just the ability to make something happen — to move it, heat it, light it up, or make a sound. It wears lots of costumes, but two of them run the whole roller-coaster story:

Here's the neat part: those two are really two pockets of the same savings account. Lift a coaster car to the top of a hill and you fill its height pocket — you've banked energy by working against gravity. Let it go and gravity spends that height, dropping it straight into the motion pocket: the car speeds up. At the bottom, the height pocket is nearly empty and the motion pocket is full. Then the car climbs the next hill, motion pours back into height, and round it goes.

But energy has a whole wardrobe of other costumes, too, and it slips between them constantly:

Transfer vs transform.

Transfer means energy moves from one object to another while keeping the same form. When you pass a moving football to a friend, the motion energy transfers to them — same energy, new owner.

Transform means energy changes from one form into another. When that football slows and stops on the grass, its motion energy transforms into a tiny bit of heat. Same energy, new costume.

Here's a kitchen example that uses both at once. You plug in a kettle: electrical energy transfers in from the wall through the cord, then transforms into heat in the metal coil, which transfers into the water until it boils. Three handoffs, one unbroken trail of energy — and not a single drop made or lost along the way.

A roller coaster does both moves, second by second — and so does almost everything around you. Keep these two words in your pocket; we'll use them the whole way down.

Drive the coaster. Watch the bank.

Drag the start height (or use the slider), then press Release. As the car runs, the height bar pours into the motion bar and back — but watch the dashed line: the total never moves. That's conservation.

Friction doesn't destroy energy — it hides it.

In a perfect, frictionless world, that coaster would run forever: height into motion, motion into height, total unchanged. But real coasters slow down and finally stop. So where did the energy go? Did the law break?

Flip the Friction toggle in the demo and watch carefully. The height + motion total does shrink — but a new heat stripe grows by exactly the same amount. Friction is the rubbing between wheels, rails and air; it transforms a little motion energy into heat every second, warming the track and the air around it.

So the energy never vanished. The grand total — height, plus motion, plus heat — still adds up to the same number it started with. The books always balance, as long as you remember to count the heat. That warmth is just energy in a costume you can't see.

You can find this heat in real life. The brakes on a big coaster get genuinely warm by the end of a busy day. Rub your hands together hard and they heat up — that's motion energy turning into heat right in your palms. A drill bit grows hot, a bouncing ball never quite returns to the height you dropped it from, a car's tyres warm on a long drive. Every time, the "missing" energy is sitting there as heat, spread thin into the surroundings.

And that's the honest catch. The heat doesn't disappear, but it does become hard to use. Once energy spreads out as gentle warmth in the air and the rails, you can't easily scoop it back up to lift the coaster again. The total never changes — but useful, concentrated energy slowly leaks into messy, scattered energy. That one-way drift is why no machine runs forever, and why we keep needing fresh fuel, food and charge.

Why the first hill is always the tallest.

Next time you spot a roller coaster, look hard at that first big climb. On almost every ride, it's the tallest hill of the whole track — and now you can explain exactly why.

The car is given one fixed lump of energy: the height energy it earns at the top of that first climb. After that, it's on its own — there's no engine pushing it around the loops. It can swap that energy between height and motion as often as it likes, but it can never make more. So it can never rise higher than where it began. If a later hill were taller than the first, the car would run out of motion energy partway up, stall, and roll back down.

That's why every hill after the first has to be shorter (and friction quietly steals a little more on every lap, so they shrink even faster). The first hill sets the energy budget for the entire ride. Conservation of energy, working away quietly at the theme park — and you can prove it yourself in the demo above: the car never climbs higher than the height line you released it from.

Every action is an energy relay.

Energy rarely changes form just once — it runs down a chain, handing itself on at every link. Pick a scene and press Next transform to follow it, link by link.

See it? Food → muscles → motion. Battery → wire → light. At every arrow the energy only changes form or changes owner — and a little always slips off as heat. Follow any chain in the world and the rule holds.

Some chains are wonderfully long. The energy in your lunch traces all the way back to the Sun: sunlight became chemical energy in a plant, the plant became your food, and your food becomes you, moving and growing. A hydroelectric dam is another: stored height energy in the water high in the hills becomes motion energy as it falls, which a turbine turns into electrical energy that may end up as light in your bedroom. Long or short, the chain never breaks, and the total carried down it never changes.

"But my phone runs out of energy!"

It really feels like energy gets used up and disappears. Your phone dies. The coaster stops. Your legs get tired. Surely the energy is just... gone?

Here's the twist: it isn't. When your phone "runs out," the chemical energy in its battery didn't vanish — it transformed into light from the screen, sound from the speaker, radio waves to the cell tower, and a lot of heat (feel the back of a phone after gaming). Every joule is still out there in the universe, just scattered into forms that are too spread out to be useful to you.

That's the honest version of "using energy." We never destroy it. We just transform tidy, concentrated energy into messy, spread-out energy — mostly heat. The total stays exactly the same; it only gets harder to gather back up.

Follow the energy.

Five quick calls. Remember the golden rule: energy is never created, destroyed, or "used up" — only transferred and transformed.

Five for five — you can follow energy anywhere now. 🎉