Lab 9: Physics 4A (centripetal force with a motor) Daniel Guzman

Daniel Guzman
Physics 4A.
Lab 9: Centripetal force with a motor



The objective for this particular experiment is to come with a clear model, which shows the relationship that exists between the angular velocity and the angle theta for an object that is rotating.

Description of the apparatus and the experimental procedure:

The apparatus for this experiment consisted of an electric motor that was mounted on to a surveying tripod, a long shaft that was oriented vertically, a horizontal rod that was mounted on a vertical rod, a long string that was attached to the horizontal rod, a rubber stopped attached to the end of the string  , and a ring stand that that had a piece of paper sting out.This apparatus was powered electrically and was used for the entire class to repeat multiple trials.
The experimental procedure for this particular experiment consisted first in taking measurement of the apparatus described above due that the dimensions are important to come up with the desired  model. Once the measurement of the apparatus were taken, we had to come up with a mathematical expression, which would relate the angle theta at which the object is rotating to the angular speed of the object,Once this mathematical expression was approved by the professor the entire class started to record the measurements using the apparatus. The measurements recorded included the time for ten rotations passing a fixed mark so one would know precisely when to to start and stop the timer, the other measurement that we had to do was to measure the height at which the the stand was because the height at which it is at every trial would be important when determining the angle theta at which the object is rotating, the same exactly process was repeated for another 5 trials in which the height and the time for ten rotations changed due that the power at which the motor was functioning was increased, which changed the data for the other trials; nevertheless, the same process was done for all the trials.

Mathematical expression that relates the angular speed to the angle theta

Data Table

The data collected for each trial was the time to complete 10 rotations and the height at which the rod will hit the paper that was sticking out on the rig clamp. These were the only two measurements necessary to be able to model the relationship that exists between the angle theta and the angular velocity.

Example Calculations

These calculation were done on the the excel data sheets using the data collected in the experiment, the same calculations were done for every single trial.

Conclusion

This particular lab yielded very precise results due that the apparatus used worked very well, reason why it yielded very precise results for the desired model. Some of the main aspects or reasons why the results were accurate was that the angular speed at which the rod was rotating was kept constant, which is very important when measuring the period of the rod. If the period was correct the theoretical angular speed would be correct, and this would allow one to make a correct comparison between the theoretical and experimental angular speeds. The model that related the angle theta and the angular speed was very accurate, this was proven by plotting the actual omega and the theoretical omega and obtaining a slope of one, which lets one infer that the values compared are equal. Also the percent error calculations were very small, which lets us assume that the model attempted was correct. The sources of error in this experiment can come from measurements made by the group for instance. measuring how tall was the apparatus, or the length of the string. Another source of error for this lab can come from doing a miscalculation or from imputing a wrong value in the data sheets, the error that comes from the apparatus is minimum due that the apparatus worked very consistently through the entire experiment.

Percent error calculations