Lab 22 Physical Pendulum Lab

Lab 20

Purpose:

Predict an expression for the period of various physical pendulums. Verify the predicted value with the value getting from experiment. Learn to find out a physical pendulum’s period by calculating and by Logger Pro and video camera.

Theory:

In the first part, we need to get the center of mass of different shapes so that we can determine the momentum of inertia of them at the center of mass. By parallel axis theorem, we can derive the momentum of inertia of them at required center. Use the T=Iα where α=ω^2*Θ to get the ω. And 2π/ω is the result we want. We assume the parameter B as the base and H as height for an isosceles-triangle. When it comes to the semicircle, we use R stands for the radius of the semicircle. The result of each physical pendulums is followed. We will use Logger Pro for the experiment part to determine the period in the videos.

Setup:

Set the equipment up like the following figure. When we perform this lab, we need to make sure the clips always stay at the same places so that the pendulum will maintain the simple harmonic motion. Tapes is necessary here to fix the clips and both sides of the pendulum should be fixed. Or the clips may fall, which will make the experiment fail. Attach thin pieces of masking tape to the base of the pendulum. By this way the masking tape can get through the photogate set up for small oscillations.

Procedure:

Semicircle pendulum

Isosceles-triangle pendulum

With Logger Pro, we can get two values of time from the result plots. For semicircle pendulum, the experiment result is 0.665700 s determined by Logger Pro. For isosceles-triangle pendulum, the experiment result is 0.761826 s determined by Logger Pro. Actually it is quite close to the true value.

Conclusion:

The error could have come from wrong measurement for the parameters. In this lab we just take the triangle as the isosceles-triangle but the actual shape may have error and so does the semicircle. Besides, the friction we didn’t take into consideration in theory value exists in the experiment, which will have influence on the result, too. The tapes will have influence on the momentum of inertia because the radius, base and height is possibly influenced.

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