Lab 6: Rotational Motion I: The Inclined Plan

University of MichiganPhysics Department

Mechanics and Sound Intro Labs

Inclined Plane Experiment

Although it may seem daunting, rotational motion is fairly straightforward. In many ways it is analogous to the linear motion that you have studied previously. Rotational motion can be examined using the same principles of energy and momentum conservation that you have used previously. The equations that accompany these laws take a slightly different form, but at their root, they are based on the same physical principles. So begins your three part study of rotational motion which includes this lab, the rotating bar in Lab 8, and the gyroscopes of Lab 9. Your understanding of rotational motion will also help you understand two-dimensional collisions in Lab 7.

The inclined plane set up that you will use to study the moment of inertia of several objects.

Your apparatus today consists of an inclined plane with a groove down the center and two photogates. A photogate is a device that records the time at which its light beam is broken by some object. In this lab, you have two photogates close together, and you will use them to determine the average velocity of a rolling object as it passes between them. You have been provided with several round objects: a ball and four disks.

PhotogatePhotogates

It is important that you understand on at least a basic level the concepts of moment of inertia and rotational kinetic energy before you begin this lab, so make sure you consult your lab manual for a discussion of these topics.

A dramatization of the workings of the photogate. The photogate has an invisible beam where you see the red line in this photo. The photogate is triggered when this beam is broken.

You will measure the moments of inertia of several objects, including objects having similar shapes but different mass distributions. These will result in different moments of inertia, even though the objects may have the same mass. By the time that you finish this lab, you will have gained much insight into these two ideas as well as their importance to the study of rotational motion.

Various objects whose moment of inertia you will measure.

After this lab, you will be familiar with the notions of moment of inertia and rotational kinetic energy. You will maybe be surprised to see that some of these concepts arise in two dimensional collisions, which you will explore next week. You will continue to study rotational motion in labs eight and nine with the rotating bar and the gyroscope.

See you in the lab!