Experiment 3: Projectile Motion

Introduction:

A projectile is an object that moves in a plane under the influence of a constant acceleration due to gravity. A ball rolled off the edge of a table, for example, is a projectile. Once the ball is in free fall, its acceleration is constant and directed downward. In this exercise, you will determine the initial velocity of a projectile using a photogate system, and then use this information to predict the horizontal displacement of the projectile. Note that we consider here only the special case of a projectile that is launched horizontally. That is a projectile with an initial (launch) velocity that is entirely in the horizontal (or x) direction. You will find this special case discussed in your textbook.

Use the photogate as you did last week to determine the speed of the ball as it is launched horizontally off the edge of the table. BEFORE LAB predict how long it takes the marble to reach the floor if the table top is 100.0 cm above the floor (come into lab with this completed, and checked against other classmates).

Procedures:

  1. Set up the flexible molding as shown by your instructor. This creates a ramp for the ball to roll down. Be sure that the lower end of the ramp is level with the table top!!
  1. Measure the distance from the floor to where the marble leaves the ramp (initial height of the marble, yo).
  2. Using the height determine how long it will take for the marble to hit the floor. tfall.
  1. Now make sure the photogate is in position so that the marble passes the sensor at the widest part of the marble (center the sensor on the marble at the level bottom part of the ramp).
  2. Determine a start position near the top of your ramp (make sure it does not change…support the ramp). Release the marble making sure that you catch it. DO NOT ALLOW THE MARBLE TO HIT THE FLOOR.
  3. The glx software will measure the time for which the photogate is blocked. Knowing the size of the marble you will calculate a speed of the marble at the bottom of the ramp. This determines the initial launch velocity of the marble. Measure several times and use the average.
  4. Use this information to calculate where the marble will hit the floor (calculate the x from the horizontal end of the ramp in the time it takes for the marble to hit the floor).
  5. Place the supplied target at your predicted position and show your instructor that the marble hits your target at the predicted position.