Pendulum on rollerblades: Qualitative Testing Experiment

Aim

To test whether Newton's first law is applicable to a particular situation with respect to a particular reference frame

Prior Knowledge

  • Kinematics: position, velocity and acceleration.
  • Newton's First Law.
  • Reference frames.

Description of the Experiment

Daniel holds a pendulum in his hand. The pendulum consists of a bob on the end of a string and it hangs vertically. Using Newton's first law, predict what will happen to the pendulum's bob as Jeff pushes Daniel abruptly. Try and answer this question from the camera's frame of reference and from Daniel's frame of reference. Use motion diagrams and force (free-body) diagrams for analysis.

Use the following reasoning before and after observing the experiment from the point of view of (1) the observer on the floor and (2) Daniel.

BEFORE EXPERIMENT AFTER EXPERIMENT
IF If Newton's first law is correct,
THEN the pendulum bob should.........
BUT/AND the bob..........,
THEREFORE ...................................


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Questions

Remember to focus on the motion of the bob in each of the two reference frames. Did Newton's first law hold in both reference frames? If not, why not? Can you formulate a general rule in which reference frames Newton's first law is true?