What's the Difference Between Mass and Amount of Matter?

[JJBladester]

"Mass' versus "Amount of matter"

Homework Statement

I just started a thermo-fluid science course and am confused with a table showing common dimensions

Homework Equations

Dimension...Unit
Mass......kilogram (kg)
Amount of matter...mole (mol)

The Attempt at a Solution

I thought mass was the amount of matter something had. Then what's the difference between a kilogram and a mole?

 

[gneill]

Homework Statement

I just started a thermo-fluid science course and am confused with a table showing common dimensions

Homework Equations

Dimension...Unit
Mass......kilogram (kg)
Amount of matter...mole (mol)

The Attempt at a Solution

I thought mass was the amount of matter something had. Then what's the difference between a kilogram and a mole?

A mole is a count of particles (atoms, molecules, etc.) comprising something. Mass refers to that something's inertia and/or response to a gravitational field.

 

[JJBladester]

A mole is a count of particles (atoms, molecules, etc.) comprising something. Mass refers to that something's inertia and/or response to a gravitational field.

I'm thinking back to my 4th grade science teacher's saying: "Matter is anything that has mass and takes up space."

The "has mass" part means that the matter resists being pushed by an external force (interia) and that the matter can be tugged by gravity.

Is this correct?

The "takes up space" part means that there's no such thing as a "point mass" in which something could have matter but would be physically dimensionless, right? It's funny how often we use point-mass approximations in basic physics courses.

 

[gneill]

I'm thinking back to my 4th grade science teacher's saying: "Matter is anything that has mass and takes up space."

The "has mass" part means that the matter resists being pushed by an external force (interia) and that the matter can be tugged by gravity.

Is this correct?

In a simplistic way, yes, it is correct. Quite suitable for 4th grade science. At deeper levels physics recognizes three types of mass: Inertial mass (the resistance to be accelerated), corresponding to the m that appears in the formula f = ma; and active and passive gravitational masses that appear as M and m in the formula f = GMm/r², where f is the force that M produces on m. In practice, thanks to the Equivalence Principle, all three masses have the same numerical value for all three cases.

The "takes up space" part means that there's no such thing as a "point mass" in which something could have matter but would be physically dimensionless, right? It's funny how often we use point-mass approximations in basic physics courses.

This is another one of those things that gets modified by a deeper look. It turns out that certain fundamental particles, like the electron, are point particles to the very best of our ability to measure. For these we treat them as point particles and place an upper bound on their possible size (experiment shows that they cannot be larger than this, usually fantastically tiny, size).

 

[JJBladester]

Thanks gneill... Very informative! I am going to study the Equivalence Principal to go even deeper.