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?
