It would be easy to set up an experiment with a cup, some water and a little bit of twine to demonstrate how circular motion results in centrifugal force through inertia.

Just drill three little equidistant holes in the cup, string bits of twine of equal length through them so you can spin it freely, fill the cup with a little bit of water and, well, spin it freely

Just be sure none of the twine is going to snap or come loose while you're spinning it - that would be bad!