eli5: What (if any) is the difference between an engine and a motor?

Question

I’ve heard these words used interchangeably over the years, with engine being more prevalent. Is there any difference? Why is a small gas-driven device like a lawnmower commonly said to have a motor, while what is under the hood of a car is almost always referred to as an engine?

In: 160

Answer 1

In the context I hear a lot (propulsion) motors are simple and engines are complex. Motors directly convert fuel to motion while engines mix fuel/oxidizer ratios for controllability. A firework with solid fuel uses a rocket motor; a spaceship that mixed liquid fuel and oxidizer to throttle thrust uses a rocket engine.