# I need a unit Conversion

1. Jul 9, 2015

### led20

Hi ALL
i need to unit Conversion :
from: 28.8 Volts/(Meter/Second) to (.............) Volts/(Inch/Second)
from: 28.8 Volts/(Meter/Second) to (.............) milliVolts/(milliMeter/Second)
Thanks

2. Jul 9, 2015

### Mentallic

Hi and welcome to PF!

Let
Volts = V
Meter = m
Second = s
Inch = in

then
$$\frac{V}{m/s}=\frac{Vs}{m}$$
while
$$\frac{V}{in/s}=\frac{Vs}{in}$$

So if you were given a problem that said, for example, the metal costs $10/m, then could you figure out how much it costs per inch instead? That is, what is the value of x such that $$\frac{10}{m}=\frac{x}{in}$$ If you can figure this out, then your problem is essentially the same because we can ignore the Volt-seconds in the numerators since they're both equivalent (think of them as merging into the$ symbol in my example).

3. Jul 10, 2015

### led20

Do you can , give me more Explain

Are you mean , like this:
(v.s/m)=(v.s/in)
(28.8v*1s/1m)=(xV*1s/39.4in)
then
28.8 v(m/s) = 1135 v(in/s) ?????

++++++++++++++++++++++++
your example:$10/m to x$/in
i thenk
1m=39.4in
$10/39.4in =$0.254/in

4. Jul 10, 2015

### led20

Thanks, now I understand (Excellent)

1 m/s = 39.4 in/s
28.8v/(m/s) / 39.4v/(in/s) = 0.73 v/(in/s)
then
28.8v/(m/s) = 0.73 v/(in/s)
it's good
from: 28.8v/(m/s) to (.........)mv/(mm/s) ???

5. Jul 10, 2015

### Mentallic

You can make it more simple for yourself by ignoring a lot of the common units.
$$28\frac{V}{m/s}=x\frac{V}{in/s}$$
We know that 1m = 39.4in, therefore we convert metres to inches by making that substitution wherever we see metres.
$$28\frac{V}{39.4in/s}=x\frac{V}{in/s}$$
And cancel all of the common units on both sides (which is the same as dividing both sides by $V/(in/s)$) to get
$$\frac{28}{39.4}=x$$

Now for the next question, again, do the substitutions as I've just shown you. 1000 millivolts = 1 volt, 1000mm = 1m.

Note: remember we are striving for simplicity, so in your first problem, you could have cancelled common factors by going straight from

$$28\frac{V}{m/s}=x\frac{V}{in/s}$$
to
$$28\frac{1}{m}=x\frac{1}{in}$$
by cancelling V/s. This helps to draw focus onto the problem at hand and not get messed up with all of the units.

6. Jul 10, 2015

### led20

http://im86.gulfup.com/ckruO5.png [Broken]

Last edited by a moderator: May 7, 2017
7. Jul 10, 2015

### Mentallic

Very good, but you don't need to do it in 2 steps. Do it all in 1.

$$28.8\frac{v}{m/s}=x\frac{mv}{mm/s}$$
Converting the LHS (left hand side):
$$=28.8\frac{1000mv}{1000mm/s}$$
Cancelling the 1000's
$$=28.8\frac{mv}{mm/s}$$

Hence x=28.8

8. Jul 10, 2015