M-CM 3: Forces on a body in circular motion in a vertical plane

PIRA: 1D50.40

Equipment: pail of water, large glass tumbler of water. The pail is in Set 5, Cabinet 3, Shelf 1 while the tumbler is in Room 4.

Procedure: If a pail partially filled with water is slung with sufficient speed over the head, the weight of the water is not sufficient to supply the force necessary to make the water move in such a highly curved path and the bottom of the pail will push on the water. The water cannot fall out.

The same experiment can be performed with a glass tumbler as well. Twist the arm around so that the palm of the hand is up. Place the tumbler on the middle and ring fingers while using the index and little fingers to support the tumbler from the sides. You can then move the tumbler over the head with the mouth always toward the center of motion if the motion is clockwise from your viewpoint and you use the right hand. Or, you can start with right hand palm up, support the tumbler as before, and make the motion counter-clockwise from your viewpoint.

In neither case can the student see the water surface during the operation; he merely observes no spillage (unless you are clumsy at the start or finish). A transparent pail with dyed water would be an improvement.