Author: Alyssa Jordan
Partners: Julia Fisher & Kirsten LeVan
Date: December 8, 2015
Partners: Julia Fisher & Kirsten LeVan
Date: December 8, 2015
Pendulum
Purpose
The purpose of this lab is to use a pendulum to investigate radial forces.
Theory
A pendulum bob moves in a circular path and thus, has centripetal force, or acceleration. This centripetal acceleration is caused by the tension in the rod. The weight, however, also affects it and must be subtracted from the tension to find the centripetal force. The velocity and centripetal force have a parabolic relationship. This means the centripetal force is dependent on the square of the velocity which is an independent variable.
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Experimental Technique
Measurements will be taken of the constants in this lab. These are flag length, radius of the circle, and mass and thickness of the bob. An equation will be derived to calculate the centripetal force. As stated above, the centripetal acceleration is caused by the tension in the rod, but the weight, however, also affects it, and must be subtracted from the tension to find the centripetal force. In order to subtract the weight, the force sensor will be zeroed. This means the force that appears on the screen will be the actual force and no weight must be subtracted from it. The pendulum will then be set up, and go through a trial run. Velocities and forces will appear on the screen. My group is investigating how velocity affects the centripetal force, so multiple velocity points will be recorded along with their corresponding force. This information will then be compared to the calculated velocity figured out using the derived equation.
Data
Analysis
This graph represents the parabolic relationship between velocity and centripetal force.
Conclusion
There are three factors that affect the centripetal force on a pendulum bob as the pendulum swings back and forth. They include mass, velocity, and radius. In this lab, we chose to investigate how velocity affects centripetal force. After completing the experiment, we used the equation we derived earlier to figure out the calculated mass. The percent difference was relatively small for most of the velocities. However, a three velocities had a percent difference over 5%. Some possible reasons for the differences between the measured and calculated values of the centripetal force are accuracy when measuring the radius since it was difficult to line it up perfectly, paradox in all measurements, and the pendulum bob moving slightly side to side when swinging back and forth. Velocity contributes most to the error in the lab because there are more elements that affect its measurement. Mass and radius are simple measurements that require one tool to measure quite easily. Velocity is measured using a whole system of things. To improve the outcome of the investigation, more trial runs should be held. The pendulum bob should be released at the same height each time and the bob moving side to side should be minimize as much as possible.
References
Bowman, Doug. "Pendulum Lab." Lahs Physics. Web. 6 Dec. 2015.
Giancoli, Douglas C. "Circular Motion; Gravitation." Physics: Principles with Applications. 5th ed. Upper Saddle River, N.J.: Prentice Hall, 1998. Print.
Giancoli, Douglas C. "Circular Motion; Gravitation." Physics: Principles with Applications. 5th ed. Upper Saddle River, N.J.: Prentice Hall, 1998. Print.