Title: Ballistic Pendulum
Tools and Equipments : Ballistic Pendulum apparatus, meter stick, photo gate timer.
Purpose: To use the ballistic pendulum to determine the initial velocity of a projectile using conservation of momentum and conservation of energy. To verify that energy conservation and momentum conservation can be used with a ballistic pendulum to determine the initial velocity of a projectile, its momentum and kinetic energy.
Procedure: The ballistic pendulum apparatus consists of a launcher, a projectile, and a pendulum. Attached to the swinging end of the pendulum is a bucket designed to catch the projectile and hold it, creating an inelastic collision. The bucket rests directly in front of the launcher, right at the exit point of the projectile. Once the launch mechanism is released, the projectile enters the bucket and the arm swings up, moving past a grooved plastic strip. A ratchet mechanism on the bucket slides past each groove, allowing motion up but not back down. Once the pendulum stops (kinetic energy is fully transferred to potential), it stays locked in place recording the maximum height of the swing.
THEORY:
In a perfectly inelastic collision, a bullet is fired into the stationary pendulum, which captures the bullet and absorbs its energy. The stationary pendulum now moves with a new velocity just after the collision. While not all of the energy from the bullet is transformed into kinetic energy for the pendulum (some is used as heat and deformation energy) , the momentum of the system is conserved. By measuring the height of the pendulum's swing, the potential energy of the pendulum when it stops can be measured. In the case of a pendulum total mechanical energy is conserved. So kinetic energy of the pendulum (after firing) is fully converted to potential energy. Thus the pendulum's initial velocity can be calculated. Using the law of conservation of momentum, the velocity of the bullet can be...