Pendulum Lab
By: Julia Banning, Megan Nanovic, and Taya Wentz
December 8th, 2015
Purpose:
In this lab, the measured and calculated centripetal forces will be discovered and compared by using a pendulum and photo gate sensor. |
Theory:
The mass hanging from the pendulum follows a circular path due to the tension in the rod. In order to find the radial force in this experiment, we used the equation of radial force = mass(velocity) ^2 = radius. From the free body diagram displayed, we found that the tension minus the weight equals the radial force, also. |
Experimental Technique:
A rotary motion sensor was utilized in order to determine the velocity of different masses. Then from that, we plugged in the mass, velocity, and radius into an equation to solve for radial force.
We made sure to have the center of the mass in between the sensors on the photo gate. We used the short rod for our experiment.
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Data and Analysis:
In this lab, we changed the mass of the bob on the pendulum while keeping the radius and velocity relatively the same. The graph displayed shows the first run that was measured:
From this graph and the data table, we used the following equation in order to solve for the Radial Force:
The answer for the first Radial Force would be 1.89 N when calculated, from the experiment it was 1.78 N. Since the answers were slightly different, a percent difference needed to be found, so we used this equation:
The percent difference resulted to be 1.50% for the first run.
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Conclusion:
During this lab, it was discovered that the centripetal can differ for different masses. Some factors that could affect the swing of the bob are the mass of the bob, the rod length, how high the rod is released from (velocity), and the placement of the mass in between the photo gate sensors. Probable reasons that the measured and calculated centripetal forces could differ are the placement of the mass in the photo gate sensors and the measurement of the radius. If the center of the mass is not placed directly in between the photo gate sensors, then the velocity and force results could be skewed a bit. Also, if the radius changes even the slightest and is not taken account for in the equation, the results could be different. Of the measurements that were made, the mass of the rod and the bob was probably the biggest contributing factor to the difference in the accepted and experimental force. The velocity could be a large factor, too, but we did not truly measure that ourselves, the photo gate did. In order to improve the outcome of this experiment, we could place a marker to let us know where exactly to drop the bob from, which would result in the same initial velocity for each mass. Also, the bob could be more accurately placed in between the photo gate sensors to obtain a better reading. Overall, this lab taught us that the centripetal force differs due to the mass of an object hanging from a pendulum.
During this lab, it was discovered that the centripetal can differ for different masses. Some factors that could affect the swing of the bob are the mass of the bob, the rod length, how high the rod is released from (velocity), and the placement of the mass in between the photo gate sensors. Probable reasons that the measured and calculated centripetal forces could differ are the placement of the mass in the photo gate sensors and the measurement of the radius. If the center of the mass is not placed directly in between the photo gate sensors, then the velocity and force results could be skewed a bit. Also, if the radius changes even the slightest and is not taken account for in the equation, the results could be different. Of the measurements that were made, the mass of the rod and the bob was probably the biggest contributing factor to the difference in the accepted and experimental force. The velocity could be a large factor, too, but we did not truly measure that ourselves, the photo gate did. In order to improve the outcome of this experiment, we could place a marker to let us know where exactly to drop the bob from, which would result in the same initial velocity for each mass. Also, the bob could be more accurately placed in between the photo gate sensors to obtain a better reading. Overall, this lab taught us that the centripetal force differs due to the mass of an object hanging from a pendulum.
References:
Bowman, D. LAHS Physics Weebly. Pendulum Lab. lahs.physics.weebly.com. 2015.
Giancoli, D. Physics, 5th Edition. Chapter 5.
Bowman, D. LAHS Physics Weebly. Pendulum Lab. lahs.physics.weebly.com. 2015.
Giancoli, D. Physics, 5th Edition. Chapter 5.