Eli5: how can you roll start a manual vehicle but not an automatic vehicle?

Question

Eli5: how can you roll start a manual vehicle but not an automatic vehicle?

In: Other

Answer 1

A manual transmission is like a bicycle, you move the wheels by moving the pedals, but if you are riding downhill then the pedals will rotate by themselves because the wheels move the chain whether you want it to or not. When you hit the bottom of the hill you can put your feet on the pedals and your motion is already “started”. Engines need to be running at a certain speed to keep themselves going, and if you can get it moving fast enough to reach that speed then the car will start.