AbstractThe purpose of this lab was to find the coefficient of kinetic friction when a cart runs along a track. All variables needed to be measured and calculated, including; acceleration, mass, vertical and horizontal net force, with a final goal of calculating the coefficient of kinetic friction between the cart and the track.
IntroductionThis lab explored the concept of various forces being applied on an object. While only one variable is being asked to find, other forces must be considered to calculate the variable that is question. In the case of this lab the unknown variable that was to be found was the coefficient of kinetic friction (the proportionality between kinetic friction and normal force) between the friction cart and the track.Therefore, the coefficient will increase in value when the surfaces are more textured. To find this variable, acceleration, mass and other forces were calculated to then go on and solve for the coefficient. When solving this force related equation it must be completed in parts, vertical and horizontal. One must move through each equation before it is possible to solve for the final variable, each step that is completed will gain more information which will then lead one to be able to solve for the final variable.
HypothesisIf acceleration, mass, and force of gravity are known, as well as the net force, then the coefficient of kinetic friction of an object can be found.
Materials |
MethodAn electronic scale was used to measure the car's mass and the hanging weights mass, and the recorded. the car was then set upon the track about 20 cm away from the end of the track. A string was attached to the end of the cart and was also tied to a hanging weight. This string was then rested on a pulley wheel, so that the cart remained on the track in its original position and the hanging weight hung close to the track above the floor. A logger pro motion detector was set up at the other end of the track approximately with the same 20 cm still remaining between the cart and censor. The censor was used to measure the acceleration of the cart as it was pulled down the track. When the motion censor was ready five trials were conducted by having someone release the cart and calculating the acceleration and then recording the results. From this information the average acceleration was calculated using the formula below and then used to solve for the coefficient of friction using the combination of formulas listed below.
EquationsDATAAll the measured variables were constant throughout each trial, as the acceleration of the cart varied slightly. It ranged from 0.8410 m/s/s to 0.8593 m/s/s.
With all the variables measured, the coefficient was calculated, resulting as 0.00355.
DISCUSSION and analysisThe purpose of this lab was to experiment with the concept of the force of friction, and whether or not the coefficient of kinetic friction can be determined while only been given the mass of the objects used, acceleration, and the force of gravity. The hypothesis of the lab that was stated at the beginning was proven through this experiment, as a value for the coefficient was determined using the information that was measured. Most aspects of this lab were expected and predicted before the actual experiment. The coefficient was pretty expected, it resulted in being 0.00355, which is between 0 and 1 which is what was predicted and also most coefficients of friction between surfaces are in that range, so naturally this was an easy prediction. An unexpected aspect was the accuracy that each trial of acceleration had compared to the other. they all resulted in staying very close in range to the other 4 and only slight variation in decimals occurred. This was unexpected because in past experiments to keep the acceleration consistent throughout a lab has been a difficult task, however this did not seem to be an issue during this lab.
sources of errorA few experimental errors occurred in this experiment that could have potentially influenced the data, changing the results. Firstly, in the experiment an experimenter would release the cart by moving their finger, this lead to potential human error. In that, it is impossible to ensure that each time the cart was released an measured that it left from exactly the same point on the track. Another source of error is when using the motion detector when measuring the acceleration. As the acceleration is quite sensitive it will read and track and movement that appears to be closer to the censor than the cart. Therefore when releasing the cart the experimenter could have gotten in the way of the censor, in which it would effect the data collected. In addition to the other sources, there was also a piece of felt attached to the bottom of the cart to increase the friction being applied, however the friction that was being applied could have potentially been slowly decreasing as each trial was completed and the felt became more worn. All of the sources listed above could have played a part in the data being slightly inaccurate to the true values.
Further ResearchFor further research, perhaps another experiment could be conducted comparing how the coefficient of kinetic friction changes as the materials vary. For example, a cart with a rubber bottom could be experimented with, observing how this different material changes the coefficient. The experiment could also extend the displacement of the cart so that force of friction has a longer period of time to be applied.
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