Rubber Band Physics: Measuring Weight* and Mass

Photo: Rhett Allain

What’s the difference between mass and weight and how do you measure both of them? Yes, that’s what we are going to do — measure these two things with a rubber band.

What’s the difference between mass and weight*?

And why does weight have that asterisk? OK, let’s start with mass. This is a measure of how much “stuff” is in an object. I mean, if you think about it — everything that you see or touch is just made of three tiny little things: the electron, the proton, and the neutron. So, in a sense the mass is just how many of these things are in the object.

There’s another analogy I like for mass: the number of Lego pieces in an object. Suppose we ONLY used the 2x4 blocks. In that case, the mass would just be a count of how many pieces you used. Notice that this is different than the volume.

Photo: Rhett Allain. Same mass Lego, different volume.

The mass is measured in units of kilograms or grams. If you are an imperial unit person — the unit for mass is the slug. True.

OK, what about weight? This is the gravitational force exerted on an object. We usually do this on the surface of the Earth where the gravitational…