What is a Transmission?
A transmission is a machine that transmits power from one place to another, and allows control over how much power is transmitted. In the case of automobiles, the power being transmitted is the output rotation of the engine, and the destination is the tires. Automobiles need a transmission in part because the engine output spins faster than the wheels should spin. Another reason is the need for a balance between torque and power.
A vehicle as simple as a bicycle even has a transmission. The sprockets, gears, and mechanisms that allow you to change the bike speed while you ride are collectively a transmission. When riding a bike up a hill it is very difficult to pedal in fifth gear, but very easy in first gear. This is because the bike is transferring a different amount of power from your legs in first gear than it does in fifth. In fifth gear the pedals and tires spin at a one to one ratio. In first gear the pedals spin around once, but the tires spin around only a fraction of a complete rotation. This means you have to pedal more times to get up the hill, but it’s less work each rotation!
This is what automobile transmissions do to save gas and prevent stress to the vehicle and its components, except the process is much more complicated and there are a lot more gears and pieces!