Science made FUN

Newton's first law of motion:

An object in motion will remain in motion unless acted upon

by an external and unbalanced force.

So to show Julian just what this means we made this contraption

and balanced a cup of water on it....

Then I told him to swing it.

He was nervous at first.

He got wet.

He dropped the cup a few times. But then .. he got it.

I told him to swing it over his head.

He did with apprehension. But all was well.

He expected that water to plop on his head, notice how he is

waiting for it to happen.

It didn't.

So, in the case of the cup swinging, the cup sends the water outward, the string

is the external force sending the cup in a circular motion. The water continues

to move in a linear motion so its pushed against the bottom of the cup.

Centripetal force is at work here.