LAB 8

PhysicsLab8 Tuesday, August 17, 2010 Name __________________
Dr Dave Menke, Instructor

I Title: Simple Harmonic Motion

II Purpose: Study Simple Harmonic Motion using a plumb bob pendulum.

III Equipment
1. String, yarn, or cord ≥ 1.0 meter long (or as close as possible)
2. Weight - to make a plumb bob pendulum (washers?)
3. Stop Watch, face watch, digital watch, clock, or other chronometer
4. Meter stick or metric ruler
5. Protractor


IV Procedure (Some of this is similar to the Gravity lab)
1. Obtain, or make, a length of string or cord that is very close to 1.00 meter long. Slightly longer is better than slightly shorter.
2. Attach a weight to one end of the string to create a plumb bob, that we will call Bob.
3. Attach the other end of the string to some stationary object (door hinge, ceiling, weighted ring stand, etc.). Do NOT use a primate because it is not stable or other mammal to hold Bob because it is not stable.
4. Measure the length of Bob exactly (to the closest millimeter) after you have set it up. This will be from the point of connection on top to the middle of the weight. Record this length (we will call the length “r”) as accurately as possible.
5. Put the Data in the Table below; one column is for the number of the trials; another for the time (in seconds) for each cycle. And a third column for amplitude in the x-direction.
6. Have one of the lab partners pull the pendulum back, to an angle of θ = 45° (try to be exact; use protractor) as seen in the diagram a
7. Measure the x-component of the Bob's motion. If the string pendulum is exactly 1.0 meter long, and if the angle is exactly 45°, then the x-component will be (1.0 m) Sin 45° = 0.707 m = 70.7 cm. Thus, when you measure the x-component, it will be very close to 70 cm. This will be your original (and maximum) amplitude.
8. Simultaneously, release Bob and depress the stop watch button to start the time “running.” It is best to have the same homosapien release Bob and operate the stopwatch (the same brain controls both hands).
9. Allow Bob to swing freely as long it can. Every time that it returns to its starting point, note and record the time, and the distance. For example, at t = 0.00 s, the x-component will be (about) 70 cm. The next time that it comes back, about 1.8 seconds later, the x-component will be less, maybe 65 cm; next time, maybe 60 cm; and so forth. If you find it very difficult to do both the time and the x-component distance, you may substitute that data that you gathered for Lab #2 about Gravity. Keep the pendulum swinging until it stops, or, nearly stops. If you need to create another table to extend the data, please do so.
10. When done with gathering the data, plot the data points on a graph, with time in seconds, t, along the horizontal (left-right) and amplitude (length of x) along the vertical. Connect the dots as smoothly as you can.
11. Determine the period of oscillation using the graph of data.

V Data & Calculations:


Trial Time (sec) Amplitude (cm)























VI Results:
The purpose if this laboratory (Example of Simple Harmonic Motion) was / was not achieved due to:

VII Error Analysis:
A. Quantitative Error: NA

B. Qualitative Error:
1. Personal -
2. Random -
3. Systematic –

VIII Questions:
1. What is the period of oscillation?
2. What is the maximum amplitude?
3. What is the average periodic decrease in amplitude for each cycle?
4. List 4 items in your life and your world that oscillate.