Determining the weight of unknown objects

[<Valcrum_x>]

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

[LazerFazer]

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

[Klaynos]

You'd need to do it on a frictionless surface, else you wont get a linear graph for smaller forces...

[Klaynos]

damn double posts...

[LazerFazer]

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.

[Klaynos]

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...

[LazerFazer]

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?

[Klaynos]

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...

[Severian]

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.)