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

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Mass and amount of matter are distinct concepts in physics, where mass is measured in kilograms (kg) and represents an object's inertia and gravitational response, while the amount of matter is quantified in moles (mol) and counts the number of particles. A mole indicates the number of atoms or molecules in a substance, contrasting with mass, which does not directly reflect particle count. The discussion highlights that matter is defined as anything with mass that occupies space, emphasizing that there are no point masses in reality. However, some fundamental particles, like electrons, are treated as point particles in physics. Understanding these differences is crucial for deeper studies in thermodynamics and fluid science.
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"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?
 
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JJBladester said:

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.
 


gneill said:
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.
 


JJBladester said:
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).
 


Thanks gneill... Very informative! I am going to study the Equivalence Principal to go even deeper.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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