Twirling Penny

Twirl a penny on a hanger to explore circular motion and how seat belts and banked roadways protect occupants during turns.

Key Questions

• What forces keep a penny on a twirling hanger?
• How does Netwon’s Second Law of Motion help to explain how seat belts protect occupants during rollover crashes?
• How do banked curves on highways help vehicles safely negotiate sharp turns?

Student Directions

1. View the Introduction video.
2. Download and print the Student Activity Sheets.
3. Start the activity and answer the Analysis Questions as you work through the Procedure.
4. In Part 2, follow your teacher's tips and safety instructions to successfully twirl a penny on the tip of a coat hanger.
5. Safety Note: Everyone must wear safety glasses until all groups have stopped twirling their hangers and groups must stay far enough apart to make sure no one is in the path of a twirling hanger.
6. View the Conclusion video and finish answering the Analysis Questions.
7. (Optional) View the "Twirling Tray" and/or the "Curve Ball" demonstration videos located in this lesson's Video Gallery (see above) to review Newton's first law of motion, centripetal force, and circular motion.

“Centrifugal” force: There is actually no such force as centrifugal force. Rather, it is a term that has been inaccurately used by people to describe the feeling of being pulled outward when moving in a circular motion (such as driving rapidly around a sharp turn in a vehicle or riding a rapidly spinning amusement park ride).

Centripetal force: an inward pushing or pulling force that causes an object to follow a circular path of motion. Objects will not move in a circular path without a centripetal force acting on them.

Friction: the force that resists the motion of any two objects in contact with each other.