# PHYS310 Lab 14 Torque And Rotation

Experiment 1: Open Door Torque

Questions

1. How did the force required to move the door vary as you moved toward the hinges? How did the speed of the door change?
2. Assuming you applied the same force at each position of the door; describe how the applied torque varied as you moved closer to the hinge.
3. Assuming that the door is relatively thin, the moment of inertia will be the same as that of a rod rotating about an axis at its end.* If the mass of the door is 10 kg and its width is 1.5 m, find the angular acceleration of the door after applying a 50 N pushing force (about 10 lbs) at a) 1 m from the hinge, compared to b) 20 cm from the hinge.
4. Explain why door handles are positioned where they are, and not closer to the hinges.

Experiment 2: Rotating Ruler

Questions

1. How much effort was required (approximately) to rotate the ruler when you reduced the end mass by a factor of two?
2. Which clay setup produced the largest moment of inertia? The smallest? Explain why in terms of the relationship between torque and angular acceleration. Make sure to incorporate the distance from the axis of rotation in your answer.
3. Estimate how much more clay you had to add in step 5 for the moment of inertia for each setup to appear the same.
4. Use the information in Table 1 to show that it requires four times as much mass at half the distance from the center in order to produce the same moment of inertia. Assume the ruler mass is negligible.

Experiment 3: Static Lever

Table 1: Balancing force applied to lever at varying distance

Questions

1. How did the required force vary as R1increased?
2. Determine the applied torque at each distance (make sure to use the correct distance!) to complete the above table. Comment on your results.
3. How would you expect your data to change with an R2 value half of what you used above?
4. Write an expression equating the torque applied by the spring scale and the mass. Rearrange this to create an expression for the applied force F in terms of R1, R2, the total mass m, and g.
5. Make a plot of the force F vs. R2/R1 using the graph paper. Draw a line of best fit through your data, and measure the slope. m = _______________
6. What does this slope value represent? Find the percent difference from the known value. (Hint: compare your expression from Question 4 with the general slope-intercept form y = mx +b.)

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