Phys4A Physical Pendulum Lab Kevin Nguyen

Kevin Nguyen
09 June 2017
Lab Partner: Jose Rodriguez
Physical Pendulum Lab

Purpose: The purpose of this lab is to find the expressions of the period for physical pendulums. Then verify the expressions by comparing the predicted periods to the experimental periods

Theory:

In this lab, we are finding the value of the period for the triangle with the axis of rotation on the apex and the half circle with the axis of rotation on the midpoint using the concept that

 net torque = Inertia of shape x angular acceleration

We are using the first and third shapes.

 We then derived the inertia and center mass (from the axis of rotation) of the shapes.

For the triangle with axis of rotation on the apex.

For the Half circle with axis of rotation at its midpoint

Then we used the Torque = I alpha equation to solve for angular velocity.

Summary:

First we set up the apparatus like this. 

The tape is added to keep the paperclip attached to the triangle. The strip of notecard is used so that the photo gate kept track of the triangle's period as it oscillates back and forth.

Unfortunately, there was no picture of the semi circle with the axis of rotation at the midpoint, but it was set up similarly to the triangle.

Then set up a graph by bring up the physical pendulum file and ran the program. 

The period of the triangle with axis of rotation at its apex is 0.8627 seconds

The period of the semi circle with axis of rotation at its midpoint, which is 0.6949 seconds

Then compare the experimental value to the predicted value.

The percent error for the calculations are

When comparing the experimental period to the calculated period, we found that they were both very similar to each other as indicated by the very low percent difference from each other (3.41% for the semi circle and 0.7546% for the triangle). It was safe to assume that the mass wouldn't affect the period very heavily since mass does not affect the period of the triangle according to Newton's second law. The masking tape would have affected the period more since the masking tape affects the dimensions of the shapes, so the period of the shapes may have been greater than its true value.

Some external factors that may have affect our values from the experiment include air resistance, since air resistance slows down the shape's angular velocity as it moves back and forth, and friction between the hook and the paper clip, which would have also slowed down the shape's angular velocity.