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# physics mechanics question. watch

1. Hello everyone.
I'm stuck on this physics question, despite having tried many times.
The question says explain using the equation pressure + 0.5*density *speed^2 =constant, how base units may be used to test the homogeneity of physical equations.
I would appreciate any help given
Thanks
2. An equation has to be homogeneous to be valid - it doesn't necessarily mean it'll be correct, but if it is inhomogeneous it is definitely incorrect. Homogeneous means that the units on both sides of the equation are the same.

Secondly, you can only add or subtract physical quantities that have the same units - if you think about it, it makes no sense to add a length to a volume. However, you can multiply quantities with different units.

This can provide you with information about the validity of an equation, and the best way to do this is to convert to base units.

In this particular case, you should try and show that pressure and 0.5*density*speed^2 have the same base units. If they don't, you can't add them, and the equation isn't valid. Secondly, since both sides must have the same units, you can work out the units of the constant

Hope this helps.

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