Description:A small mass is attached to the inside center of a beaker using a light spring. The cup is held upside down, with the mass hanging out of the cup, then released from rest. Ask the students what will happen when the cup is released: (a) the mass will extend the spring, like a parachute, due to air pressure pulling on the cup, (b) the mass will be pulled up into the cup by the spring, or (c) the cup will fall with the mass in its original position. Check out the videos below to view the action.