A force acting in the direction of motion of a body speeds it up. A force acting opposite to the direction of motion of a body slows it down. There must be some sort of compromise between the statements 1. and 2. above. A force acting at right angles to the direction of motion of a body neither speeds it up nor slows it down. We have forgotten something.
Motion has two aspects - a speed and a direction .
The throttle and brake forces leave the direction unchanged but alter the speed. The sideways force leaves the speed unchanged but alters the direction. Now, back to the supermarket car park. 1 says it all. Once it was known that the planets orbit around the sun, the question of what caused the orbiting was a natural one to ask.