# Grouping all of the units at the end? I.E. F=ma = 2.3*424.3 [kg*m/s]

1. Sep 2, 2013

### WK95

In some papers I've read, I've seen the authors write down all of the units at the end. For example

$F=ma = 2.3*424.3 [kg*m/s^2]$

In high school, I've never seen the teachers or textbooks write like this. How common is this is method? Assuming one keeps track of their units properly, I like this method because it feels more organized.

2. Sep 2, 2013

### Dick

It's the usual thing to collect all of the units in a product together, for exactly the reason you cite. Do it, it's a good thing to do.

3. Sep 2, 2013

### PhanthomJay

Yes as long as you keep track of units, this is a good way to do it. Remember that the short name for a kg.m/s^2 is a Newton, the SI unit of force.

4. Sep 2, 2013

### WK95

Thanks. I'll use this more knowing that its a proper practice. Just ot make sure i'm doing it right, is this correct in format?

$F=9.8m [m/s^{2}]$

What about for something like y = 59 - 4x?
Would I group the units in brackets after each term or at the end of the whole thing?
For example, would it be
$y = 59 [unit] - 4x[otherunit]$

Last edited: Sep 2, 2013
5. Sep 2, 2013

### Dick

The format isn't terribly important, you don't need brackets. Just collect all of the units at the end like you did before, kg*m/s^2. I'm not sure what your example is. m[m/s^2] isn't the units of a force.

6. Sep 2, 2013

### Dick

End of the whole thing. If the two terms you are adding or subtracting have different units, then there is a mistake someplace. You can't add things with different units.

7. Sep 2, 2013

### WK95

The first m is a variable for mass. But it looks the same as the unit for meters

Also, the example was just random numbers. The variable of x has units that would make "otherunit" into the "unit" but I didn't put down the units for x since it's still an unknown value.

8. Sep 2, 2013

### Dick

Ok, fair enough. But using 'm' as a variable for mass when you are are also using 'm' to designate meters is asking for confusion. If you are collecting units, then use dimensionless quantities for the variables, like the numbers you used before. I.e. don't say mass=M. Say mass=M*kg. So M itself has no dimensions.