Understanding why cars dont move when engine is reving

This might be a stupid question but i'm learning, when a car is on, either manual or auto, why doesn't the car move like surely the power is still going to the driveshaft, and all your doing is opening the throttle when pushing the accelerator, so why doesnt the power go to the wheels? or like being at a traffic light with the engine on and breaks on? Why doesnt it move forwads? Is it because of the differentials? Sorry if this makes no sense
TAAAANKS:confused:

Uhmm- Errh- That's is why there is a torque converter between engine and every automatic transmission- think of it as a fluid clutch- that only transmits torque, (or rotation) when engine rpms go up- the more power required to move the car, the faster it has to turn. When idling, the engine turns and tranny doesn't because the fluid is moving slowly in the torque converter (pump) as rpm increases so does fluid pressure and now the tranny starts to turn.

The only time the engine and tranny turn the same speed is with TCC lock-up- a solenoid allows the engine to lock onto the torque converter housing to drive both engine and tranny at same speed- this is designed for fuel economy.

Overspeed tranny means the tranny (output) is turning faster than the engine- and is achieved by using different gears in the tranny....

Uhmm- Errh- That's is why there is a torque converter between engine and every automatic transmission- think of it as a fluid clutch- that only transmits torque, (or rotation) when engine rpms go up- the more power required to move the car, the faster it has to turn. When idling, the engine turns and tranny doesn't because the fluid is moving slowly in the torque converter (pump) as rpm increases so does fluid pressure and now the tranny starts to turn.

The only time the engine and tranny turn the same speed is with TCC lock-up- a solenoid allows the engine to lock onto the torque converter housing to drive both engine and tranny at same speed- this is designed for fuel economy.

Overspeed tranny means the tranny (output) is turning faster than the engine- and is achieved by using different gears in the tranny....

Thank you that makes alot of sense !!

The differential is what allows the drive wheels to turn at different speeds, so that the car can turn- otherwise it would go straight and/or one wheel would have to slip on the pavement whenever turning.

My big tractor has locking differential and when it is engaged, I can't turn- the front wheels just slide when turned- so you have to unlock it manually (switch on dash) if you want to turn at the end of the field....