Physics Practicals

# Torque

PHY180 Module 10 - PHY180 Student Guide April 18, 2023, 2:27 p.m.

## Activity 1

Use some string to hang a mass from the end of the meter stick. Find the balance point (the location where you can hold the ruler and mass up using only one finger). Record the distance between the end of the meter stick where the mass is and the balance point. Call this variable d. Change the mass many times and record the value of d each time.

If you plot 1/d as a function of mass, your graph should be linear. You can then fit the graph and find the mass of the ruler. You will have to do a torque calculation and rearrange the variables to figure out how to determine the mass of the ruler from your graph. Do so. Compare your value (with uncertainties) to the mass of the ruler as determined by a mass scale in your room.

## Activity 2

You have a yo-yo. Stand the yo-yo up so it can roll on your table. Pull the string in each of the three configurations diagramed below and observe in what direction the yo-yo rotates.

Explain your observations using the concepts of forces and torques. Explain each of the three situations twice: once using the middle of the yo-yo as the pivot point and once using the point of contact between the ground and the table as the pivot point.

## Activity 3

You have a gyropscope. Wind the string up then pull it quickly to the gyroscope spins rapidly. With one hand flip the gyroscope so that its rotation goes from clockwise to counterclockwise (as seen from above) and back again. Describe what you feel. Carefully note which way the gyroscope moves compared with how it is spinning and how you are trying to flip it. Now explain your observations in terms of forces, torques and angular momentum.

Next, put the spinning gyroscope on its stand. Do this by holding it at about 45o and then release it. Describe the motion of the gyroscope. What part of the motion is the precession and what part of the motion is the nutation?

Finally, for fun, there is a gyroscope with an LED inside a case. If you get it spinning and then hold it in one hand and move your hand correctly, you can speed up its rate of rotation a lot. Your TA should be able to help you.