Ballistic Pendulum Demonstration

 

This demonstration is about conservation of mechanical energy. When the spring is released the ball shoots off the post at some initial velocity. To figure out how fast it was going, we watch how high the pendulum swings: the pendulum converts the kinetic energy of the ball as it leaves the post, to potential energy as it rises against gravity. Once we measure how high the pendulum swings, we can compute the potential energy, and figure out how much kinetic energy it must have had when the ball was fired. Since kinetic energy depends on velocity, we can find out how fast it was going.

Loading Pendulum       Pendulum Ball         Pendulum Stopped

Used in Lab:

A different setup of the ballistic pendulum is used in PHYS 103, 115, and 211

Equipment:

  • Caste iron ballistic pendulum apparatus, ball should be stored inside the pendulum
  • LoggerPro sensors probably can't pick up the velocity with enough accuracy to predict the height, but if you just want to show the smooth change of velocity it may be worth it

Setup Instructions:

  • Load the ball onto the post at the end of the spring loader.
  • Use the accompanying lever to push the spring back far enough to lock it with the trigger lever.
  • Make sure that nothing is in the way of the pendulum, and pull the trigger.
  • Measure the height at which the pendulum stops.
  • Work through the calculations to find the initial velocity.

Apparatus Notes:

  • The higher measured heights tend to be more accurate. When the pendulum lands lower there is likely more energy loss in the system.

Safety Information: Do not use fingers to load the spring. Do not place any body parts in front of the spring while it is loaded. Serious injury may result.
Location: Demo Room Shelf R1
JHA