# Measurement

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### Mhelz

Feb 26, 2010, 2:17:31 AM2/26/10
to ode-users
is where sbook directed me to... so I might as well try, anyway, I'd
like to ask what is the basic unit of mass in JMEPhysics.... when we
use setMass() function, are we talking about grams here...?

### Danny Price

Feb 26, 2010, 6:33:17 AM2/26/10

'grams' is a measure of 'weight'. Weight is the product of mass x gravity. A gram on mars is not the same as a gram on Earth.

I don't think ODE specifies a unit for it's masses because the gravity is variable. The closest science unit would be the mole or molecular mass.

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### Oleh Derevenko

Feb 26, 2010, 6:44:12 AM2/26/10
Gramms are the measure of mass, not weight.
And gramm on Earth is the same as Gramm on Mars: it's a quantity of stuff that if you need to achieve acceleration of 1 kilometer per second squared for it you need to apply force of 1 Newton to it.

Oleh Derevenko
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### Danny Price

Feb 26, 2010, 7:52:09 AM2/26/10
I looked it up and you are correct. I was taught the old definiton "the absolute _weight_ of a volume of pure water equal to the cube of the hundredth part of a metre". Thanks for the clarification.

### Jon Watte

Feb 26, 2010, 12:57:34 PM2/26/10
ODE uses whatever units you want, as long as they are consistent (it applies no conversion constants internally).
Most people feel most comfortable using kilos, seconds, meters, but you can use whatever consistent set of units you want.

Sincerely,

jw

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