Eugenia and David pull on each other: Observational Experiment

Aim

To construct a relation/rule relating the force Eugenia exerts on David and the force David exerts on Eugenia when either one of them pulls the rope.

Prior Knowledge

  • Kinematics: position, velocity and acceleration.
  • Graphing skills.
  • Newton's first law.
  • Newton's second law.
  • Reference frames.

Description of the Experiment

  • Carefully observe what happens when David pulls on Eugenia and Eugenia pulls on David.
  • Does it seem possible for David to pull on Eugenia without starting to move himself? Does it seem possible for Eugenia to pull on David without starting to move herself?
  • Addtional Information

    Eugenia's mass with gear: 52kg
    David's mass with gear: 83kg


    Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click HERE.

    Questions

    For one particular trial when either David pulls or Eugenia pulls:

    • Decide what you need to measure to determine the speed of Eugenia and the speed of David after the pull is over.
    • After the speeds have been determined, can you find the acceleration of David and the acceleration of Eugenia?
    • What assumptions should you make in order to find their accelerations during the time interval when the pull was exerted?
    • Use the information you have found and previously established relation between acceleration and the net force to compare the forces they exert on each other.
    • Repeat for the other trials
    • What can you conclude about the strength of the pull of David on Eugenia as compared to Eugenia's pull when Eugenia pulls on David?
    • What can you conclude about the strength of the pull of Eugenia on David as compared to David's pull when David pulls on Eugenia?