II. Procedure 

A. Initial Measurements 

  1. Measure the length of the pendulum. 
  2.  Measure the mass of the pendulum cup in the following way: remove the pendulum arm from the apparatus and bring it to the digital balance.  Place the blocks of wood vertically next to the scale.  Make sure the pendulum is parallel to the table with the cup on the scale and the pendulum head on top of the wood.  
  3. Measure the mass of the projectile. 
  4. Set the spring tension in the gun to its maximum setting. 

B. Determination of Pendulum Velocity and the Initial Velocity of the Projectile

M = combined mass of pendulum cup and ball,
L = length of pendulum, and
V = velocity after impact.

Using the conservation of energy,

 

  1. Return the pendulum to the vertical position. Make sure the angular protractor mounted on the support is properly zeroed. 
  2. Fire the gun five times and record the rise of the pendulum after each shot as measured by the angle on the protractor. Remember to read the scale to 1/10 th of the smallest division. 
  3. Use a spreadsheet to record the angles and to calculate the velocity after the collision using the conservation of energy for each shot. 
  4. The momentum, P, is defined as the product of mass and velocity, and is a quantity we will devote a chapter to later on. The momentum of ball and holder after the collision is Pafter = MV. The momentum before the impact is that of just the ball since only the ball is moving: Pbefore = mballv0, where v0 is the initial velocity of the ball. The law of conservation of momentum tells us that Pafter = Pbefore so that

v0 = MV/mball.

Calculate v0 for each shot and then calculate the average with a 90% confidence interval.