Fairly easy question about mass density:?

Question

If you have a ball of clay, and mold it into a bunch of shapes, does the volume change? i know the density and the mass do, im not so sure about the volume

Answer 1

Very nice question because it is so tempting to go astray!

1.) Does the volume change? No, it does not. We need a thought experiment. Think about painting all the walls in a room with a gallon of paint. Suppose --walls, ceiling, floor-- it takes exactly one gallon. Now if someone asks you (sure it is an odd question, sort of) what is the volume of the paint on the walls, ceiling and floor, what will your reply be? Well, one gallon. No matter how thinly you spread the paint, you will always have one gallon. So, your ball of clay will always have the same volume no matter how you manipulate it.

2.) Does the mass change? Well, unless you add more clay, or throw some clay away, the mass will be the same, too. Back to our painted room. Suppose you weighed the room (silly, I know), and weight the paint before you started painting. How much would the room weight when you were done? Yeah, yeah, yeah, it would be the sum of the two. Painting a thin coat doesn't change to weight of the paint in total.

3.) Well, if volume and mass do not change how about the density? Well, density = mass/volume and since neither of those changed, well, then density didn't change either.

Now let's go back to paint, and fess up a few details. What happens when paint dries? Yes, water (or solvent) evaporates. We lose mass, and we lose volume as well (shhh, don't tell!). So density may have changed. But hey! It was a thought experiment!

HTH

Charles

Answer 2

Assuming you didn't add any foreign matter to the clay, the mass should not change. Density is a property of the material and it doesn't change. That makes the volume the same no matter what shape you make it. If you think you make something super thin, the volume will be reduced. It is not true, You can never make the thickness zero and for very thin shapes, the area will be very large.

Answer 3

Volume, mass, and density all stay constant.