On Sun, 4 Sep 2016 16:32:44 -0400, Jeff Wisnia
wrote:


I'm always interested in learning new things to try and spotted this one
in a book of puzzles SWIMBO just gave me. I just had to try it.

Put a paper or Styrofoam cup with water in it on a kitchen or postal
scale and note its weight. Leave it on the scale. (A glass of water
might be too heavy for the scale.)

Now stick a finger or two into the water without touching the side or
bottom of the cup and watch what happens.

The scale reading increases.

Did you expect that? I didn't.

I'm sure any physicists here will explain why.

Jeff

You really just weighed the amount of water displaced but since the
specific gravity of a finger is pretty close to 1 it is a good
approximation. If you did it with a lead sinker, you result would be
different.