# What is the meaning behind multiplication in Physics?

1. Feb 13, 2013

### actionwolf83

I understand the meaning behind Division fundamentally, such as one Magnitude being proportional to another. For example, v=m/s means meters per second. Or as a ratio, it means for every one second there is one meter.

What I can't seem to wrap my brain around is the concept of multiplying different types of Magnitudes together. Take for example Amp Hours (Ah) or A*h. What is the significance or meaning behind this? It is not a ratio, and have trouble understanding the meaning behind different types of units being multiplied together as opposed to one being divided by the other.

2. Feb 13, 2013

### phinds

Your example of amp-hours is a good one. Suppose you have a battery that will produce 1/2 amp at 24 volts. OK, that's nice to know, but suppose you need it to power a 24 volt light that requires 2 amps and you need it to do that for 10 hours. Will it do it? You have no idea.

BUT ... if you know that it is rated for 5 amp-hours, then you DO know whether or not it will do what you need it to do.

3. Feb 13, 2013

### Staff: Mentor

Say it like this: 5 amp-hours is 5 amps for an hour.

4. Feb 13, 2013

### rcgldr

Probably not. I think you want the 24 volt light to also require 1/2 amp.

Then it can drive a 1/2 amp load for about 10 hours.

Since you know it's a 24 volt battery, then you know that the total energy stored in the battery is:

(24 volts) x (1/2) (amp) x (5 hours) x (3600 seconds / hour) ~= 216000 Joules

Last edited: Feb 14, 2013
5. Feb 14, 2013

### A.T.

So you understand v=d/t but don't understand d=v*t ?

A is the ratio here: A=C/s So: C=A*s or: 3600*C=A*h

6. Feb 14, 2013

### Staff: Mentor

Ampere-hours is a measure of the amount of charge.

$$C(coulombs)= A(\frac{coulombs}{sec})×3600(\frac{sec}{hour})×h(hours)$$

7. Feb 14, 2013

### Travis_King

In general it sort of means "Applied over..."

As A.T. pointed out, d=v*t is basically read, "Distance is equal to the velocity applied over t amount of time"

Or "Mass is equal to the density of the fluid applied over some volume, V."

8. Feb 14, 2013