# Difference between Mass and Weight?

1. Apr 16, 2010

What is the difference between Mass and Weight?

Because i often get confused about it.

It's concerned about Newton's second law.

I'm trying to learn it by myself.:)

2. Apr 16, 2010

### mgb_phys

Mass is how much stuff there is in an object - it doesn't change.
Weight is the force that the earth pulls on the mass with.

So on the moon you would have the same mass, but only 1/6 the weight.
In a falling elevator you would be weightless but not massless.

3. Apr 16, 2010

### D H

Staff Emeritus
These are two rather distinct definitions of weight. The gravitational force that the Earth exerts on a person in a falling elevator is no different than the force that the Earth exerted on this unfortunate person while he was waiting for the elevator. In this context, weight is just a synonym for gravitational force.

We call the person in the falling elevator "weightless" because that person truly does feel something quite different than the person waiting for the elevator. The same feeling of weightlessness occurs when a skydiver first jumps out of an airplane and when an astronaut is in a quiescent (non-thrusting) orbiting vehicle. That second definition of weight is called apparent or scale weight.

Finally, legally and colloquially, weight is a synonym for mass rather than having units of a force. In this context, a one pound can of peas weighs one pound anywhere on the Earth, in a space station, on the Moon, and in deep space.

4. Apr 16, 2010