In the Classroom

Note: The ping pong ball accelerator used in the science carnival demonstration requires vacuum pumps capable of extremely low pressures. As most non-university settings cannot obtain these types of materials, this write-up is designed around a spring propelled ‘catapult’ style launcher.

Science Disciplines

Physics

Topics

  • Acceleration
  • Air Resistance

Materials

  • Plastic Spoon
  • Mouse Trap
  • Plyers (optional)
  • Tape (scotch, electrical, or duct will work best)
  • Ping pong ball

 

Safety

  • Mouse traps by design carry enough force to seriously injure human fingers, and other body parts. Rat traps carry even more closing force. The mouse trap should never be held on the “danger” side where the hammer meets the platform.

 

  1. Use plyers to remove the holding bar, and catch, while leaving the spring and hammer in place. (optional)
  2. Place a spoon between the hammer and platform, along one of the side shafts of the hammer.
  3. Tape the spoon, to the hammer securely, so that it will not come off or move during launch.
  4. Tape the platform down to a stable surface for launching.
  5. Prime the catapult by pulling it back to the lever to the launching side of the platform, and adding the payload to the bucket.
  6. Once the danger side of the platform has been cleared, release the lever, and send the payload flying.

 

Questions

  1. Why did the ping pong ball fly so far?
  2. How would the spring size change the outcome?
  3. Why doesn’t the ball simply get smashed into the table as the trap swings around?
    1. Or why did it get smashed into the table? (this is typically a problem with the curvature of the spoon, as the ball will be thrown outwards as it accelerates around the circle)

Explanation

The lever acts on the ping pong ball with a very rapid force along a circular path. Just like a car driving too fast around a circle, the ping pong ball is thrown from the circular path and continues on a perpendicular path to the circle from the point where it was released. As the system’s mass is very low, and the spring is preloaded to a high tension rate, it accelerates the ping pong ball very quickly to speeds that are typically faster than what a normal human could throw a ping pong ball.