PhysicsLAB Lab
Video Lab: Marble Collides with Ballistic Pendulum

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This lab is based on a Direct Measurement Video called A Ballistic Pendulum: Marble Collides with Pendulum released on the Science Education Research Center (SERC) website. The copyright for this video belongs to Independent School District 197 in Mendota Heights MN. The project is partially funded by a National Science Foundation Grant (#1245268) awarded in September 2013.

The following lab directions were designed for use in my Honors Physics I class and only represent one method of analyzing the data provided in the video.

Upon analyzing the information in the video, you will be able to calculate the momentum of a marble and pendulum both before and after a collision. Then we will discuss conservation of momentum and any changes in KE that occurred during the collision. Before taking any measurements, view the video several times to acquaint yourself with its scenario.
 
Refer to the following information for the next four questions.

This initial section of questions deals with the marble's average speed prior to colliding with the pendulum. Note that this portion of the movie has a frame rate of 2400 frames/sec (it is shown in 80x slow motion).
 
On which frame has the center of mass of the marble travelled 2.5 cm from the end of the pneumatic cannon? 

On which frame does the center of mass of the marble reach 50 cm? 

How much time, in seconds, does the marble take to reach the 50-cm mark? 

What was the marble's average speed before impacting with the weighted mass on the end of the pendulum? 

Refer to the following information for the next two questions.

According to the background information given with the video, the mass of the marble is 10.0 ± 0.1 grams and the mass of the pendulum arm assembly is 578.2 ± 0.1 grams. Now we will investigate the magnitudes of the marble's momentum and KE before its collision with the pendulum.
 
Calculate the total momentum in the marble/pendulum system before the collision. 

Calculate the total KE of the marble before the collision. 

Refer to the following information for the next five questions.

Our next section deals with calculating the average speed of the marble/pendulum system immediately after the collision. Note that the frame rate of the video has been changed to  240 frames/sec.
 
After the collision, what was the maximum angle through which the pendulum’s arm with weighted mass swung prior to swinging back down? 

How long is the pendulum from the point of suspension to the weighted mass’ center of mass? 

Use trigonometry to determine how high the center of mass of the pendulum arm with weighted mass and attached marble swings after the collision. 

How much potential energy does the weighted mass with its attached marble have at the top of the pendulum’s arm’s swing? 

Using Conservation of Energy, determine the linear velocity of the weighted mass with the attached marble immediately after the collision.
 

Refer to the following information for the next two questions.

In this section you will calculate the momentum and KE of the pendulum with its attached marble after the collision.
Calculate the total combined momenta of the pendulum’s arm with weighted mass and the attached marble immediately after the collision. 

Calculate the total combined KE of the pendulum's arm with weighted mass and the attached marble immediately after the collision. 

Refer to the following information for the next seven questions.

Conclusions
Do your answers for the total momentum before the collision and the total momentum after the collision verify that momentum was conserved during the collision?
 
Support your choice in the previous question. 

What is the percent difference between the total momentum before the collision and the total momentum after the collision? 

How much KE was lost during the collision? 

What percent of the dart's original KE does this loss represent? 

Was this collision elastic or inelastic? 

In this collision, what impulse did the weighted mass on the end of the pendulum give to the marble? 




 
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