# Mass and weight

1. Feb 9, 2010

### bonjour

http://en.wikipedia.org/wiki/Atomic_mass

Wouldn't this just mean all weight is mass since everything is made out of atoms?

2. Feb 9, 2010

### cepheid

Staff Emeritus
Weight and mass are two different things, because weight is an example of a force, and force and mass are two totally different things. To elaborate: the weight of an object in a gravitational field is the force exerted upon that object by the gravitational field. Mass, on the other hand, loosely speaking, can be thought of as a measure of the total amount of "stuff" comprising an object.

I haven't read the Wikipedia article you linked to, but I should point out that the statement you quoted is a statement about what names human beings have decided to assign to various quantities, and how those names are changing. It is not a statement about physics.

3. Feb 9, 2010

### Staff: Mentor

No, they are just trying to clean up the terminology. "Weight" is a measure of the gravitational force acting on an object. Weight depends on mass, but is not the same thing.

4. Feb 9, 2010

### bonjour

Isn't it illogical and irresponsible to name two different things under the same term?

5. Feb 9, 2010

### bonjour

As opposed to which other species assigning names (e2a: and making statements about physics)?

6. Feb 9, 2010

### Staff: Mentor

I agree that atomic mass is a more accurate term than atomic weight. That's why they are cleaning up the terminology. (Despite the terminology, the professionals know what is meant by the term.)

7. Feb 9, 2010

### bonjour

That's not what I asked. Nonetheless I think I have found an answer that I'm happy to go away with.

I thank you Doc Al for your own personal time that you have given me in effort of replying to my query. I am (although miles away) extremely grateful.

8. Feb 9, 2010

### JohnniG

So weight is the gravitational pull? And mass is how big something is?

9. Feb 9, 2010

### stewartcs

Weight is mass times acceleration. If you're on Earth your weight is equal to mg (g varies somewhat with your location on Earth).

Mass is a characteristic of an object that essentially tells one how much matter it is composed of.

CS

10. Feb 9, 2010

### JohnniG

Okay, thanks a lot :)

11. Feb 9, 2010

### cepheid

Staff Emeritus
Illogical, certainly. Yet, it happens ALL the time in science. (Possibly historical) names for things that make absolutely no sense given our current understanding of what they are? (E.g. Planetary nebulae). Check. The same word being used to mean two totally different things in two different sciences, or even in two different fields of study within the same science, or even in two different contexts in the same field of study in the same science? (Just think of the words "flux" and "intensity" for starters). Check.

Huh?? I fail to see how your remark is even a remotely relevant or sensible response to what I posted. I was just trying to make the point that nomenclature, is, as always, arbitrary and devised by people (i.e. it is "man-made", and the choice of name has no impact on the underlying phenomenon that it is describing. If I had replaced the term "human beings" with "people" in my sentence, would you have even made this comment?