# Understanding units

1. Feb 19, 2014

### polaris90

What does it mean to have units being multiplied rather than divided. For example 1Weber which is equal to 1Vs. Saying 1 Volt second doesn't make much sense to me. I understand if it said for example N/m. In general what does it mean to have the units being multiplied rather than divided?

2. Feb 19, 2014

### SteamKing

Staff Emeritus
What does it mean if you have units like m^2 or m^3?

3. Feb 19, 2014

### Khashishi

Well, if you are trying to cover your floor with tiles, and your room is 5m by 6m, you need 30m^2 of floor tiles. meter^2 is dimensionally different than meter, since it is a two-dimensional area, not a length. It has to be multiplied, not divided, because of how it scales. For example, a meter is 100 centimeters; therefore, a square meter is 100^2 square centimeters.

When you have a divided unit, for example, 1 meter per second--that's the same as 1 centimeter per centisecond, because you scaled down the numerator and denominator by a factor of ten.

1 volt second = 1 millivolt kilosecond, because milli and kilo cancel out when you multiply them. Capiche?

4. Feb 19, 2014

### flatmaster

Velocity has units of m/s. Velocity is the DERIVATIVE of position with respect to time.

Weber has units of V*s. Magnetic flux (Weber) is the INTEGRAL of voltage with respect to time.

5. Feb 20, 2014

### 256bits

does this make a difference for you?
1 Weber = 1 Vs
1 V = 1 Weber/second

6. Feb 20, 2014

### dauto

If you have a problem with multiplying units, one can only imagine what you would think of more abstract units such as fractional dimensions...

7. Feb 20, 2014

### polaris90

@flatmaster
The only one with a reasonable answer, that helps understand it. I did some reading an you were correct about it. However, I my question was more general and used the Weber as an example. It is clearly understood when you have units such as meters per second, which means a change of a meter per every second. Or if we said one kilogram per meter squared, which means there is an amount of an kilogram for every meter in the x direction and meter in the y direction. In a more generalized form, it says a change of a unit for every change of this other unit. But if you have units being multiplied( not such as $m^2$ which I mentioned above), is there a more generalized way to explain it?

8. Feb 20, 2014

### CthlhuLies

So you are asking what a unit of measurement squared is? As in km² or m²?

9. Feb 20, 2014

### polaris90

No, as I already mentioned above in the text you quoted. My question is when you have two different units such as Newton Meters, which according to my reading is equal to the amount of force of one Newton applied to an arm perpendicularly which is one meter long. I understand how to work with the units when it comes to mathematical calculations. But I would like to have a more conceptual understanding of how the units work when they are being multiplied.

10. Feb 20, 2014

### dauto

I'm really baffled by that question. So, multiplying meter by meter to get m2 is OK, but multiplying meter by Newtons to get Nm some how is causing you conceptual difficulties. How come?

11. Feb 20, 2014

### dauto

I think there were other good answers. 256bits' answer was pretty good. You can't have division without multiplication.

12. Feb 20, 2014

### polaris90

Good point, I guess it might be because I cannot simply visualize it in my head as easily as a $m^2$.

13. Feb 20, 2014

### dauto

Stop trying to visualize it then. Ultimately unit multiplication is an abstract concept. You are performing a mathematical operation on non-numerical entities. A meter is not a number, it's a distance. A second is not a number, it's an amount of time. A meter per second is not a number, it's an amount of speed. Even though none of those things are numbers, it is correct to state that a meter per second is equal to a meter divided by a second. This operation is possible by definition. A meter per second is defined as a meter divided by a second (not as a meter for every second as you stated earlier), and a Weber is defined as a Volt times a second. That's all there is to it.

14. Feb 21, 2014

### nasu

Is it that you have problems understanding N*m as an unit but you are OK with Newton by itself?
A force measured in Newtons does not raise conceptual problems?
If this is the case, remember that N=kg*m/s^2. Now you have a problem with N too?
And N/m which you say you "understand" is "actually" kg/s^2. How do you visualize the s^2?

15. May 17, 2016

### Gudiya kumari

m^2 is the unit of area whereas, m^3 is the units of Volume. Both the units are in SI system.

16. May 17, 2016

### ebos

Hey, Gudiya.... that thread is from 2 years ago. That's OK, I forget to check the date often too.