Video file
PIRA Classification: 1G20.30.
Description: A styrofoam cup with a hole near its bottom is filled with water. When the hole is open water flows. When the cup is dropped with the hole open water does not flow. In the observer reference frame this means that the cup and water in it fall with the same acceleration. In the frame that falls with the cup this means that there is no gravity.
Special Instructions: The cup falls pretty fast, and it is hard to see whether water flows anyway. So the instructor should drop the cup with the hole facing them, and success is judged based on their clothes staying dry. A somewhat riskier method is to use colored water and look at the final color of their clothes.
Condition: Good.
Setup time: 2 minutes.