what is different between a motor and an engine?

Answer 1

Engines convert heat to mechanical energy. Motors convert electrical, pneumatic or hydraulic energy to mechanical energy.

In certain contexts, the term "motor" is used to refer to an engine such as in motorcycle and motor sports. Some people may use the word motor to refer to an engine in almost any context. However, the term "engine" is rarely if ever used to refer to a machine that converts electrical, pneumatic or hydraulic energy to mechanical energy.

Answer 2

An engine is anything created by "ingenuity".
If you follow the origins of the words engineer etc. they come from Latin "ingenium" that means ingenuity and mental aptitude, so an engine could be anything created by an "engineer", being a person that has these abilities - it's much more obvious in most other European languages than English, where "ingenieur" is the standard title.
I think the definition in TheFreeDictionary is too restrictive and they are in fact defining a motor.

A motor is much more specific, being a device intended to create motion. Again you can follow the etymology and find the origins. There's no restriction on the type of motion, linear, rotating, oscillating, or on its power source. I prefer the second definition in TheFreeDictionary which starts:
"A device that converts any form of energy into mechanical energy."

Answer 3

It seems that all engines are motors, but not all motors are engines. Usually, we think of an engine as something that is powered by expansion of a gas within an enclosed space. Therefore, a gasoline engine and a steam turbine engine are correctly named. Anyone agree with my definitions?

Answer 4

Engines are defined as a mechanical device that converts heat energy to mechanical energy.
Examples of engines are:

1. External combustion-- steam(piston or turbine)
2. Internal combustion-- gasoline or diesel piston engines
3. Turbine engines (like jet or turboprop engines)

Motors generally refer to mechanical devices that generate motion via electro magnetic energy like electric motors. Some refer to molecular systems that produce motion as motors.

Now for the confusing part! In nearly every way shape or form each of these names has been used interchangeably. For example, we speak of rocket motors although the rocket motors that power the space shuttle are referred to as Shuttle Main Engines and technically rockets convert heat energy from combustion into mechanical energy of motion.

Did you understand all that?