Central Forces: Pail of Water, Pail of Nails

Photo shows the demonstration used at the University of Texas at Austin.

---

Concepts Conveyed:

• The string exerts a centripetal force that keeps the pail in circular motion.
• Because of inertia, the contents of the pail always move tangentially to the pail's direction of motion, preventing them from falling out of the pail.
• The pail must swing quickly because the movement of the pail must be fast enough to overcome the downward acceleration on the contents due to gravity at the top of the swing. This is why you can hear the nails hit the walls of the pail at the top of the swing.

Instructions / Notes:

• Swing each pail QUICKLY in a large vertical circle by its handle. DO NOT SWING THE PAIL IN THE DIRECTION OF THE STUDENTS.
• Demonstrate that the effect works for liquids and solids.

---

Demo Staff Notes:

• Fill one of the large pails with a small amount of water.
• Fill the other pail with the nails.

Last updated on July 25, 2024