# [BASIC] Interpretation of multiplication

1. Apr 1, 2013

### Atran

Hello, I know this question may be absurd or very basic, but I need to know what it means when two variables with different units are being multiplied.

I need to know what multiplication is in physics, in order to make sense of formulas (such as momentum, force, energy formulas) without only depending on their written definitions.

Thanks for help.

Last edited: Apr 1, 2013
2. Apr 1, 2013

### mathman

You need to clarify what is troubling you. For example momentum = mass x velocity, where mass is scalar in units such as grams, while velocity is a vector where the components are in units of distance divided by time, such as meters per sec.

3. Apr 1, 2013

### Atran

I don't understand why momentum (p=mv) and energy (W=fd) formulas are the way they are.

I've got an intuitive feeling of momentum: the greater momentum an object has, the more resistance it has for change in motion.

I don't really understand why momentum is equal to (mv). In other words, why (mv)?

4. Apr 1, 2013

### ForumUserX

You've essentially captured it in that statement.

Think about what happens if EITHER of those quantities is 0. A massless object has no resistance to change, and a motionless object has no motion. Both or either one imply 0 momentum.

5. Apr 1, 2013

### A.T.

The formulas for energy and momentum are chosen such that those quantities are conserved under certain circumstences. That is the whole point of these two concepts. The conservation of these qunatities was deduced empirically.