# Finding Mass of Object without Scale

SirSpanky0
I need to find the mass of an aluminum rod without the use of a scale. I have all the dimensions of the rod but I just don't know the right equations etc. Thanks for the help!

Staff Emeritus
This sounds like it might be a homework problem. Perhaps you know the volume of the rod, and its density?

Maybe you're stuck finding the volume of a "rod". A "rod" could have a lot of shapes, though the first one that springs to mind is that of a circular cylinder.

I think that if this is a homework problem you'd do better if you made some effort to solve it yourself, first (the "show your work" rule) - also, there is a special forum for homework problems.

pmb_phy
SirSpanky0 said:
I need to find the mass of an aluminum rod without the use of a scale. I have all the dimensions of the rod but I just don't know the right equations etc. Thanks for the help!
You can accelerate it with a constant force and then divide the force exerted and the acceleration and that will give you the mass. Easy to say, hard to do for a lab experiment in school.

Pete

amt
pmb_phy said:
You can accelerate it with a constant force and then divide the force exerted and the acceleration and that will give you the mass. Easy to say, hard to do for a lab experiment in school.

Pete

Yes, but how are you going to calculate the force with which you accelerate? you may still need a scale.

pmb_phy
amt said:
Yes, but how are you going to calculate the force with which you accelerate? you may still need a scale.
It depends on the particular way you choose to accelerate it. If you use two charges then you use Coulombs law. If you use a spring then you use the law for springs (the name evades me at the moment).

Pete

cscott
pmb_phy said:
[...]If you use a spring then you use the law for springs (the name evades me at the moment).

Would this be Hooke's Law ($F = kx$)? Sorry if I'm wrong, I just like to think I know what's going on once in a while :tongue:

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