Physics Question (i think??) (1 Viewer)

[Ton5698]

Hi
Heres a Physics question i encountered in a worksheet:
"An astronaut on a mission to Mars uses a beam balance to measure the mass of some rock samples on the surface of the planet. The samples are returned to Earth and the same beam balance is used to determine their mass. The results from both planets are identical. Explain."

I found this very confusing and would like someone to explain this to me in detail.

 

[RishBonjour]

Haven't looked at physics in a while, but note the word "mass". The mass does not change. The astronaut could simply get the weight on the beam balance (w=m.g) and divide it by the known gravity on the surface of each body to calculate its mass.

 

[Rathaen]

The way a beam balance works is that you take the object you're measuring, and comparing the weight (or downwards force produced by gravity x mass) of the object to that of a known mass.

When the two weights equal, they will balance each other out - at this point the force F = mg of the object will be equal to F = mg of the known mass. Since both forces are equal, and the values of g are the same, then the masses of the object and known mass are the same. Looking at the way we got this, you can see that no matter what value you set g to, it will have no impact on the value of m (which helpfully fits in with the fact that mass doesn't change with variance in gravity).

Beam balances are different to say, your average bathroom scales, because they directly measure the mass of an object, whereas your bathroom scales measure the downforce and then calculate mass by dividing by g (whatever you want to set that at).