Collision Forces
An activity from the Burroughs Wellcome Student Research Program
The Science of Sports

Problem:

Collisions are a major part of any sport: bowling balls collide with pins, tennis rackets collide with balls and racecars often collide with each other. When any two objects collide they exert forces on each other. Consider the simple case of a bug colliding with a fast moving windshield. Which experiences more force - the bug or the car?

Materials

Computer

ULI and Data Logger software
OR
LabPro and LoggerPro software

2 Student Force Sensors
assorted masses
2 cork stoppers
2 carts
rubber bands
tape and string

Procedure:

ULI: On the computer open Data Logger. Plug both force sensors into the ULI and calibrate both ports. Display both ports on the same graph so that you can see data from both carts at the same time. Use the tape to attach the force sensors to the carts as shown above. Attach the cork stoppers to the hooks as shown.

LabPro: On the computer open LoggerPro. Plug both force sensors into the LabPro and calibrate both channels. Display both probes on the same graph so that you can see data from both carts at the same time. Use the tape to attach the force sensors to the carts as shown above. Attach the cork stoppers to the hooks as shown.

Exploring:

Watch the class demonstrations and record all of your observations. (Teachers: demonstrate the following collisions where the carts have equal masses.) Cart 1 and Cart 2 collide, both carts moving:


Cart 1 is moving and Cart 2 is stationary at collision:


Cart 1 is stationary and Cart 2 is moving at collision:


Use your observations above to predict what would happen in the following situations.

• What would you expect to happen to the forces and carts if Cart 1 has more mass than Cart 2 and both carts are moving when they collide?
• What would you expect to happen to the forces and carts if Cart 2 has more mass than Cart 1 and Cart 2 is stationary before the collision?
• What would you expect to happen to the forces and carts if Cart 2 has more mass than Cart 1 and Cart 1 is stationary before the collison?

  Now see if your predictions are right! For each situation; sketch the force vs. time graph, give maximum displacement values and describe the cart motion.

• Cart 1 has more mass than Cart 2 and both carts are moving when they collide
  • Graph:
    
    
  • Description:
    
    
• Cart 2 has more mass than Cart 1 and Cart 2 is stationary before the collision
  • Graph:
    
    
  • Description:
    
    
• Cart 2 has more mass than Cart 1 and Cart 1 is stationary before the collison
  • Graph:
    
    
  • Description:
    
    

  If you have extra time try some different situations. For example: What if one cart rear ends the other? What if the carts are attached by a string and one pulls the other?

Discussion:

• Describe the similarities and differences between what you predicted and what you observed.
  
• Did differing masses have an effect on the forces experienced in a collision?
  

Conclusions:

• Consider the simple case of a bug colliding with a fast moving windshield. What experiences more force - the bug or the car?
• Why does the force have a greater effect on the bug?
• How could you modify the experiment to test the bug-car situation?