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Posted

Hi

I'm ne to the whole forum thing and I have a specific reason for joining, curiosity... I want to know if anyone can help me with my problem? How will I go about to determine the mass of an unknown object without dusing a scale of any kind or density, i.e. the displacement of water.

Thank you in advance

Posted

Well, you could make use of F=ma. Measure the force required for a certain acceleration. Do this for multiple accelerations, and plot this on a Force vs Acceleration graph. The slope is then the mass.

That should work. If i'm wrong, please correct me.

 

Cheers,

LazerFazer

Posted

Well, since the coefficient of kinetic friction is the same (for all the trials), and thus the frictional force is also the same, wouldn't you get a linear graph, only not centered at the origin? Also, I'm pretty sure you can neglect air resistance, since only a small force and thus a small acceleration and consequently velocity will be used.

Posted

well, the frictional force will increase as the force applied increases, and then become constant at a certain point. That is non-linear. The trick is to reduce mew as much as possible, and then use forces which will always have the max friction...

Posted

Since FrictionForce=NormalForce*Mew, and both of those are constant, as long as you overcome the static friction (which is greater than the kinetic friction), you would have a constant friction force. Of course, this is assuming the force applied is directly parallel to the direction of motion, and to the surface. Is this true, or am I getting confused somewhere?

Posted

You're slightly incorrect there:

 

Frictional Force <= NormalForce * mew

 

Although, I think I'm probably being really idiotic, as if it's moving that means the applied force is > frictional force anyway.... So yeah ignore my ramblings, too much maths and not enough physics recently...

Posted
Hi

I'm ne to the whole forum thing and I have a specific reason for joining' date=' curiosity... I want to know if anyone can help me with my problem? How will I go about to determine the mass of an unknown object without dusing a scale of any kind or density, i.e. the displacement of water.

Thank you in advance[/quote']

 

You can't. Your first measurement is always going to be a definition of your units of mass. Then you can measure mass afterwards, but it will always be in relation to something else (ie. using a scale).

 

(In the F=ma examples people are using, you need to measure your force and your acceleration which are both using preset measurement scales.)

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