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Material Type: Lab; Class: General Physics-GTSC1; Subject: Physics; University: Mesa State College; Term: Fall 2007;
Typology: Lab Reports
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Phys 111L Fall 2007
The behavior of physical systems in general can be described in terms of standard variables such as velocity, acceleration, force, energy and momentum. Although this scheme is applicable to all classical physical systems, it is useful to used modified versions of the standard variables when describing orbital or rotational motion. The goal of this laboratory is to introduce you to variables suitable for describing the kinematics of rotational motion: angular position, angular velocity and angular acceleration.
1 Angular Velocity and Angular Acceleration: Theory Complete sections I and II of the workbook exercise, “Rotational Motion” (this is an excerpt from “Tutorials in Introductory Physics” by McDermott and Shaffer).
2 Angular Velocity and Angular Acceleration: Experiment. The laboratory is equipped with a PASCO rotary motion sensor with an attached rotating arm. The rotary motion sensor can measure angular position and velocity. There is also a PASCO smart pulley which can be used to measure linear (ordinary) velocity.
a) Connect the PASCO rotary motion sensor and configure it so that it records angular position, measured in rad/s, and angular velocity, measured in rad/s^2. b) Configure the display so that it displays graphs of angular position vs. time and angular velocity vs. time in the same window. c) You will rotate the arm at approx- imately constant angular velocity in four different combinations of fast vs. slow and counterclockwise vs. clock- wise. Using a single set of axes, sketch and label predicted graphs of angu- lar velocity vs. time for motion:
i) counterclockwise at a slower rate,
ii) clockwise at a slower rate,
iii) counterclockwise at a faster rate, and
iv) clockwise at a faster rate.
Time
Angular velocity
d) For each of the four situations above, carry out the motion by rotating the arm. Run the motion sensor, display the four observed graphs of angular velocity vs. time on the same set of axes, print this and attach it to the worksheet. e) Do your predictions and observations agree? Explain any major discrepancies that you may have noticed.
f) What is the main distinction between a graph for counterclockwise rotation and one for clockwise rotation?
3 Relationship between angular and linear speeds. For an object that rotates in a circle at a distance r from the axis of rotation, the speed is given by v = ωr (1)
where ω is the angular speed. The magnitude of the (linear) acceleration is
a = αr (2)
where α is the angular acceleration. In this experiment you will check these relationships.
a) Attach a string to the largest pulley on the rotary motion sensor. Run the string over the directional pulley and over the smart pulley. Suspend a 50 g mass from the string. b) Configure DataStudio to read smart pulley and display the graph of velocity vs. time in the same window as the graph of angular velocity vs. time. The smart pulley measures the speed with which the string moves. Describe, at any single instant, which points on the pulley and arm arrangement move with the same speed as the string. Determine the corresponding r. c) Wind the string and release the suspended mass, after clicking Start.