Lab 5 - Rotation

# Lab 5 - Rotation - Physics 7A Rotation lab(v.4.0 p 1 of 6...

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Physics 7A Rotation lab (v.4.0) p. 1 of 6 Name ________________________ Partner(s) ____________________ Lab Day/Time ________ LAB 5: ROTATION Introduction In this lab, you will investigate the physical meaning of torque and rotational inertia . As you’re working, keep in mind the big picture about these two physical quantities. Just as a force causes an object to accelerate linearly ( F net = m a ), a torque causes an object to accelerate angularly, in accordance with net = I . So, in rotational motion, torque plays the role of force: The bigger the torque, the more quickly the object’s angular speed increases or decreases. Similarly, rotational inertia plays the role of mass: A bigger I means that the object is more resistant to having its angular speed changed. This sounds simple. But former Physics 7A students tend to agree that rotational inertia, and especially torque, are some of the trickier concepts in the course. That’s why we’re doing this lab. Periodically, your GSI will stop the lab to go over central concepts. Part 1: Rotational inertia Find a rod. Grab the rod in your fist and twirl (spin) it by rotating your wrist back and forth. To make sure gravity plays no important role, spin the rod horizontally. 1. ( Make a prediction before doing the experiment. ) First, hold the rod near its end, and twirl it as just described. Then, do the same thing, but hold the rod near its middle. If you let your wrist exert equal effort both times, then you apply the same both times. In which case (if either) will the rod spin more easily? Since you generate roughly equal torques in both cases, why is this so? Explain your prediction intuitively. Now try it. If the result disagrees with your prediction, see if you can figure out why.

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Physics 7A Rotation lab (v.4.0) p. 2 of 6 2. Explain, conceptually, why the rod has more rotational inertia when pivoted around its end instead of its middle, even though the rod has the same mass in either case. ***************************************************************** Class discussion of rotational inertia. Go ahead and try the following questions now; but double check your answers after the class discussion, to take your GSI’s ideas into account.
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## This note was uploaded on 11/19/2010 for the course LECTURE 1 taught by Professor Yildiz during the Spring '10 term at Berkeley.

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Lab 5 - Rotation - Physics 7A Rotation lab(v.4.0 p 1 of 6...

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