Scale problem

[half-death]

Hello everyone,
I'm currently working on a science project which is to build a scale (not sure if it's the right word.... In French it's "balance".... It's an instrument to measure the mass). I already ran a search on Google and didn't provide anything useful. The only thing I can think of is trying to build something with a spring (once again, I'm not sure if it's the right word... In French it's "ressort"......). The problem is I have to do this in only two courses of 75 minutes.... And I don't know what kind of spring I should take, or if it has any chance to work.... Does anyone know a simpler way or have any tip??? I'd really appreciate it.
Thank you!

[UncleAl]

Imagine an automobile in neutral gear on flat ground. Try to lift it - that is gravitational mass. Try to push it - that is inertial mass. The Equivalence Principle states that gravitational and inertial mass are fundamentally indistinguishable. This is true for all chemical compositions, spinning bodies, charged bodies, magnets, superconductors... to one part in ten trillion difference/average. Measuring either one gets the job done for both.

You now have many choices. You can measure force (e.g., a spring scale and Hook's Law for small displacements). You can measure mass (e.g., a balance against a calibrated reference mass). You can create a pendulum and measure its period. You could hang it from a series of filaments of known decreasing tensile strength until one breaks. Place it on the far end and measure deflection of a cantilever (laser pointer to create an optical interferometer and use a stiff I-beam!). Place it upon the top edge of a a thin plate of Plexiglas or polycarbonate sitting on a sharp "^", between two crossed linear polarizers, and measure the fringe shift at the point of bottom contact. Hook it to an air piston (plunger of a well-lubed hypodermic syringe containig some air volume) and (P1)(V1)=(P2)(V2) at constant temperature in tension or compression. Etc.

Tall central spindle risng out of a round platterattached with a hinge or joint to an arm at its top, or maybe just a filament. Place the lump to be tested at the far end of the arm or filament and spin up the spindle and its platter at a constant rate. How does the angle the arm rises depend on the angular velocity, the length of the arm, and the mass of the object added?

[half-death]

Thank you!
It really helps. I think I will go with (P1)(V1) = (P2)(V2).... It's simple and I already worked with this law in chemistry.... Once again, thank you so much!

[Turtle]

UncleAl said "Tall central spindle risng out of a round platterattached with a hinge or joint to an arm at its top, or maybe just a filament. Place the lump to be tested at the far end of the arm or filament and spin up the spindle and its platter at a constant rate. How does the angle the arm rises depend on the angular velocity, the length of the arm, and the mass of the object added?"
___What if there are 2 arms hinged & the masses are themselves gyroscopes? How does the direction of spin of said gyroscopes affect the rise & fall of the arms as the platter & spindle spins? What other possible differences are likely to emerge?