Gears

Spinning things pass their turning on to whatever they touch. Gears that touch turn opposite ways. Things on the same shaft (an axle, or a crank, wheel, turbine, motor or generator touching a gear) turn the same way. A 💧 turbine (on the Water tab) is a spinning block too: rising steam turns it.

	Block	What it does	✋ USE
	Small gear	8 teeth. Turns the gears next to it the other way. One tooth is yellow: follow it to see which way the gear turns and how fast.	—
	Big gear	16 teeth, so it turns half as fast as a small gear it's touching (and a small gear driven by it turns twice as fast). Big gears also touch corner to corner.	—
	Axle	A rod: carries turning in a straight line, the same way round. It only joins things at its two ends: a gear beside a shaft doesn't touch it (and doesn't break it).	—
	Crank	Hand power! Red knob = stopped, green knob = turning.	stop → ↻ → ↺ → stop
	Water wheel	Turns when 💧 water flows through it. More water = stronger. A longer fall = faster and stronger: put it where the water drops.	—
	Motor	⚡ Electricity in, turning out. Put it in a loop with a battery (wires on its sides). One battery makes it as strong as a crank; more batteries, faster and stronger. Move the battery to the other side of the loop and it turns the other way. Turn it by hand and it is a generator.	—
	Generator	Turning in, ⚡ electricity out: wire it up like a battery. Its + end swaps when it turns the other way. Wire a battery to it and it is a motor. It is the same machine as the motor, fitted the other way round.	—

Follow the yellow tooth. Every gear has one yellow tooth, every water wheel one yellow paddle tip, and every turbine one yellow blade tip. On a fast gear the plain teeth all look alike, so they can seem to stand still or even creep backwards (like wagon wheels in a film). The yellow tooth never fools you: it goes round the way the gear really turns, faster on a faster gear. A gear that slows down slows down smoothly, and one that stops stays where it stopped.

Jammed! Three big gears all touching each other (in an L) can't turn: each one would have to turn both ways at once. The whole group stops and shows a red ❌ ().

Speed and strength. Everything that turns gears has a top speed (how fast it goes with nothing to push) and a strength (how hard it can push before it stops). The harder it has to push, the slower it goes, like a real motor or a real arm. A crank has strength 2. A water wheel's push comes from the weight of the water and how far it falls. One faucet falling one block through a wheel (the faucet right on top, a drain right below) makes it just like a crank: top speed 1, strength 2. More water makes it stronger: three faucets, strength 6, at the same top speed. A longer fall makes it faster and stronger, because falling water speeds up: four blocks of fall (not two) make it twice as fast and twice as strong. The water keeps the push of its whole fall for as long as it keeps falling, and gives it all to the first wheel it lands on. If it lands on the ground or in a pool first, it has splashed its push away. Water that spills off both sides of a wheel pushes it both ways, and that cancels out. Build a machine the other way round (mirrored) and its wheel turns the other way, just as fast. In a level stream it still turns, but only feebly: that water hardly falls. At the end of a pipe from a tall tank a wheel is strong too (deep water presses harder), and every cell taller the tank is makes it a bit stronger. Make the wheel the last thing in the pipe: a wheel in the middle of a pipe only gets the little the water rubs away going through it, because the rest of the push is used up where the water leaves the pipe. A turbine is a water wheel upside down: its push comes from how much steam goes through it and how far that steam rises. One burner's steam rising one block makes it just like a crank too. More steam (more burners, each under its own pot of water) makes it stronger; a taller chimney under it makes it faster and stronger. It has no left or right of its own, so it helps whichever way its gears already go (↻ if nothing else is turning them). A motor gets faster and stronger with more batteries. Two of them on the same gears add up. Two cranks turning opposite ways push against each other: the stronger one wins.

Gears change speed, not power. A small gear driven by a big one spins twice as fast but pushes half as hard. Gearing a generator up makes it spin faster, but it gets harder to turn, so the crank slows down: you never get out more than you put in.

One machine. A motor and a generator are the same machine: a coil of wire that turns between magnets. It follows one rule, both ways round:

• Turn it and it pushes electricity: 1 volt for each turn a second (a battery pushes 1 volt). Faster = more volts.
• Push electricity through it and it turns: each amp of current pushes its shaft as hard as half a crank.

The two blocks are that one machine fitted opposite ways round, so you can use either for either job. A motor turned by a crank lights a lamp just like a generator (its + end is on the other side). A battery wired to a generator spins it just like a motor (the other way round).

Generators push back. Making electricity takes work. The more lamps a generator lights, the more current flows, and the harder it is to turn. With nothing wired to it, it spins freely (only its bearings rub a little). Join its two ends with plain wire and it gets hard to turn, because a big current flows: watch the dots race. Take the wire away and it's easy again. Turn it slowly and it still makes a little electricity: a dim lamp, not a dark one. Generators wired in a row each feel all the current they make together: three on one crank are much harder to turn than one.

A spinning motor pushes back too, against the battery. That is the same rule again: it is turning, so it pushes volts of its own, the opposite way to the battery's. So how much electricity a motor takes depends on how hard its job is:

One battery's motor...	turns at	and takes
with nothing to turn	0.95 turns a second	hardly any current (0.1 amps): its own push nearly cancels the battery's
lifting a crate	0.47	about 1 amp
stalled under an iron weight	0	2 amps, the most it ever can. It lifts nothing and just gets hot

Put a lamp in the loop and you can see it: the lamp is bright while the motor is stuck and nearly dark while it runs free. (Real motors do exactly this. It is why the lights dim for a moment when a big machine starts up, and why a jammed motor burns out.) But the lamp is in the way: it holds current back, like one more coil in the row. One battery, a lamp and a motor can't lift even a crate (two thirds of an amp is the most that gets through, and a crate takes one). So for the lamp experiment below, use two batteries.

A battery and a crank on the same machine add up or fight, like two cranks:

• A battery pushing against the electricity a cranked generator makes helps the crank round. Two batteries drive it faster than the crank could ever go by itself (now the hand is holding it back!).
• A battery pushing the same way as the generator makes it much harder to turn. One battery and one crank cancel out: it stands still, with a big current that only makes heat.

A cranked generator is a soft battery. A battery pushes 1 volt however much you ask of it. A generator turned by a hand slows down when you ask for more, so its push sags. That is why six lamps side by side on one cranked generator are all dim. A stronger turner (more water on a wheel, more steam through a turbine) makes a stiffer one.

Everything happens at once: the gears and the electricity are worked out together on every tick, so a motor fed by a generator is at full speed the moment you wire it up, and a clicker or a switch can't catch anything out.

Three things to try:

1. The tell-tale lamp. Two batteries in a row, a lamp and a motor in one loop, with a gear and an axle from the motor to a winch. Let the winch turn with nothing on its rope, then lift a crate, then try an iron weight. Watch the lamp each time: nearly dark (0.2 amps), bright (1 amp, and the crate goes up), brightest (1.3 amps, and the weight stays put). Then take one battery away. Now the crate stays put too, and the lamp can't tell it from the iron weight. Why? (The lamp holds too much current back.)
2. Help the crank. Crank a generator that is wired to one battery. Tap the crank to turn it the other way. Which way is easy? Now use two batteries in a row and watch how fast it goes.
3. Swap them. Build crank → generator → lamp. Swap the generator for a motor block. What changes? (Nothing: only which end is +.)

Nothing runs forever. Every bit of turning has to be paid for. A machine turns work into exactly as much electricity, and electricity into exactly as much work, but some is always lost on the way as heat: in the coils (the more current, the more heat), in the lamps, and in the bearings. So what comes out is always less than what goes in, and a motor powered by its own generator stops at once, however you gear it. The same goes for a pump lifting water for the water wheels that turn the pump's own generator, however many wheels and gears you use: the wheels only get the push of water that falls, and the pump has to spend more than that lifting it back up. Take the battery away and it all winds down. A steam plant is the same: a turbine only gets the push of steam that rises, never more than the steam gave up, and only a burner makes steam. Turn the burner off and the turbine, its generator and everything they power stop.