I know it has to do something with speed and rotations but idk
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Think instead about gears on a bicycle. You set off and start pedalling. After a certain speed it seems like most of the effort is going into spinning your legs really fast, rather than driving the bike forwards. In other words you legs have a maximum efficient RPM. So you change gear and now your legs are spinning at a reasonable rate and you can accelerate a bit more. The gears aren’t magical though: above a certain speed it’s simply too hard work to push the pedal each time so you can’t maintain that speed even in the optimal gear.
You might ask why you don’t just start in a high gear. Well have you tried it? When you set off you have to push very hard on the pedal and even then you only accelerate very slowly. In other words your legs can only deliver so much torque.
Well a car engine is quite like your legs: it can only deliver so much torque, and it can only go up to so much RPM. So you use gears to keep the engine in the best range of RPM while the speed of the car changes.
It’s the exact same as with a bike, ever rode a bike?
Try getting away in 6th or driving top speed in 1st
First of all: what if the car didn’t have gears.
Well, then the wheels would only rotate as fast as the engine. But engines have ranges of rotation speeds they work best at, they don’t like rotating too slow or too fast. So you introduce geara to adjust the wheel speed and engine speed.
Ultimately it’s just a question about gears (as in, the spinning toothed wheels) ratios, and gears are just levers. I hope you’re familiar with levers, i.e. the further from the anchor point you are, the less force you require to move something, but the more distance you need to move the lever.
So yes, there’s speed and there’s torque. Speed is related to the distance of the lever, in higher gears in the car you’re pushing on smaller levers, so you can rotate them faster, but you need to use more force for it. Torque is the force the engine exerts on it.
In low gears, the wheels will rotate much slower than the engine (longer lever), but it allows the engine to get the car going (if you tried to do it without gears, the engine wouldn’t have enough force at low rotations to do it and would just stall), go uphill or to tow something heavy because it takes less effort from the engine.
As you shift up, you get the wheels spinning faster and so require more force to do it, but you also allow the engine to stay in its comfort range and be able to provide that force. So again, if you tried to drive slowly in that gear, the engine would stall because it would need to rotate too slow, below its comfort zone.
Of course you can skip the higher gears and just run the engine really fast, but it’s still not going to be optimal (it’s going to lose power) AND it causes wear and tear.
Electric vehicles don’t have gears do they?
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