Lab 9: Rotational Motion III: The Gyroscope University of Michigan Physics Department Mechanics and Sound Intro Labs

Precession is a motion exhibited by rotating objects which change their angular momentum when subjected to torques, in accordance with Newton’s Second Law, and whether you realize it or not, torques and angular momentum have an impact on your everyday life. If you rode your bike today, the angular momentum of the wheels helped you maintain your balance.  Food for thought: At the completion of this lab, you should be able to say whether it is better to lean to the inside or outside while turning on a bicycle.

Spinning tops wobble (precess) when they are tilted because they experience a torque due to their weight. The rotation axis of the Earth wobbles in space due to the torque the Sun’s gravity exerts on the non-spherical shape of the Earth. In this lab, we will explore Newton’s Second Law for rotating objects and the resulting precessional motion by studying the gyroscope.  This spinning top is a very simple example of a gyroscope.

You have seen a gyroscope in this course before. Recall that, in essence, a gyroscope is a wheel spinning freely about an axis. The gyroscope can be supported in a variety of ways to study the effect of applied torques on its motion. In order to observe precession, the gyroscope must have angular momentum and it must be subjected to a torque. To give the gyroscope angular momentum, it is necessary to spin it up to high angular speeds. You will use a Dremel motorized tool for this purpose. Remember, safety comes first, so be careful when spinning the gyroscope. Keep clothing, jewelry and fingers away from the spinning wheel to avoid having them pinched between the wheel and support frame and wear safety glasses.  The proper method of spinning up the gyroscope.

You need to precisely measure the angular speed of the gyroscope, for which you will use a photo tachometer (“speed-measurer”). This tool measures the angular speed of the rotating gyroscope in revolutions per minute (RPM). Aim the photo tachometer at the reflective strip on the gyroscope.  For best results, the tachometer should be held at about 30 degrees from the gyroscope axis.

You will use two different mechanical mounts to support the gyroscope for your experiments. With the first mount you will measure the precession of the gyroscope about a fixed pivot point. With the other you will study the effect of torques applied to the gyroscope suspended from both ends in space. In both mounts, it is important that you make sure that the gyroscope is secure, which you can do by ensuring that the pins which hold the assembly are firmly in place. You now should have a better idea of how to use this experiment’s equipment, and a better understanding of its goals. The mechanical mounts used in this lab.