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Uniform Circular Motion (Y 20)


Keyword: Mechanics Lab

Demonstration Description:
The direct goal of this experiment is to study a "conical pendulum", and apply Newton's 2nd law to an object moving in a circular orbit. A round weight of mass m (the "mass") is attached to a rotating shaft by a spring; you will adjust the angular velocity &omega of the shaft rotation, measure the radius rm(&omega) of the circular motion of the mass, calculate the centripetal force from F = ma and use the results to find the force constant of the spring. To simplify the analysis of your results, assume that the mass of the spring can be neglected.
You will do the following things in this experiment:

  • Measure the radius rm(&omega) of the orbit of the mass m as a function of &omega for the shaft, and interpret your measurements with a model based on two things (i) the spring obeys Hookes' law (spring force proportional to amount of stretch) and (ii) Newton's Second Law holds Fspring = mrm(&omega)^2 .
  • This model predicts rm(&omega) &rarr &infin at a critical angular frequency, &omegaC, for the shaft rotation; you will observe the approach to this behavior and understand what causes it.


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