Eugenia on Rollerblades: Qualitative Observational Experiment


To observe the motion of an object when it does not interact with other objects and when it does interact with other objects. (Friction between the floor and rollerblades is negligible.)

Prior Knowledge

  • Kinematics: position, velocity and acceleration.
  • Reference frames.

Description of the Experiment

Observe what is needed for Eugenia to start moving. Notice what happens when she interacts with other objects. Notice what happens when she does not interact with other objects.

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  • What was necessary for Eugenia to start moving? Consider the different ways in which she got moving. What did they have in common?

  • What was necessary for Eugenia to keep moving?

  • What did Eugenia have to do to stop moving?

  • What can you say about Eugenia's speed after David pushed her once? How do you know? With respect to what observer did you make your statement? What observers would see Eugenia speeding up or slowing down after David pushed her? What observers would see her moving with constant velocity?
  • Represent Eugenia' motion during the moment when David pushes her, after he pushed her (several instances) and when she stops using motion diagrams and force (free-body) diagrams. Find a pattern in those diagrams. How are the two diagrams for each instance related? What assumptions did you make?