Daniel Guzman
Physics 4A.
Lab #7 Modeling Friction Forces
Modeling Friction Forces
The purpose of this particular experiment was to model different friction forces, under different circumstances, to then compare and analyze if the model predicted for the friction forces was correct when comparing it to theoretical results.
Summary of Apparatus and Experimental Procedure.
The apparatus changed slightly in this lab due that there were five different experiments.
Instead of a water cup a hook with weights was used
Apparatus for experiment #1: The apparatus consisted of a block, a pulley, weights and a hook. The weights were placed on the hook so the car could accelerate due to the tension created in the string.
The experimental procedure for this part of the lab was quite simple due that my group and I only had to attach a string to the wooden block and to a hook that was hanging from the pulley. Once this was done we proceeded and and put wights on the hook util the block started to move. After the block started to move we stopped it and measured how much weight was hanging from the pulley and recorded it. The other trials for this experiment were the same, but the only thing that changed was that the 220 grams were put in the block every time so the hanging mass changed each trial. After the data was all recorded it was used to create a plot on logger pro.
Apparatus for experiment #2: The apparatus consisted of a force sensor, a wooden block, and a string , which was attached to the bock and sensor, so one member of the group could pull the block at a constant speed and the force would be recorded on logger pro.
The procedure for the second part of this experiment was quite simple, the first thing that we did was to calibrate the force sensor using 500 grams until the reading in the sensor reads 4.9 Newtons. Once this is calibrated a member of the group pulled the string with the car at constant speed, the data for this particular experiment was saved automatically into the laptop, the only thing I had to do was to use the statistics tool of logger pro to obtain the mean of the force exerted on the car by the person who was pulling it.
Apparatus for experiment #3: For the third experiment of this lab the apparatus consisted of a phone which measured the angle of the slope, the same wooden block used in the other parts of the experiment and a wooden board,which was the slope on which the block would slide down.
the experimental procedure for this experiment was the simpler of all experiments because we only had to tilt the board and measure the angle at which the block would slide down, to then calculate the coefficient of static friction between the block and the wooden board.
Apparatus for experiment 3 and 4 was pretty similar the only thing that changed was that in the apparatus for experiment four a motion sensor was used to measure the acceleration of the block sliding down.
Apparatus for experiment #4: For the fourth experiment of this lab the apparatus was the same as the third's experiment the only thing that was added was a motion sensor so we could measure which was the acceleration as the block slides down.
Experimental procedure: The experimental procedure for this experiment of the lab was pretty much the same as the experimental procedure for last part the only thing that changed was using the motion sensor, which helped one record the position and velocity graphs. On the velocity graph we put a trend line, which ends up giving one the acceleration that the block had as it was sliding down the slope.
Data collected for all the experiments of this lab
Graphs of plots and explanations
First plot for first experiment
On logger pro we plotted the data collected in the first experiment. on the x axis we used the mass of the block n grams and in the y axis the weight required for the block to start moving. Once this was plotted we put a linear fit throughout the points and the slope of this linear fit would give us the coefficient of static friction.
For the second experiment the force sensor provided a mean value of the force that was exerted by the person that was pulling the wooden block at a constant speed. In the x axis we used the weight of the wooden block and in the y axis we used the average force recorded by the motion sensor. After these different points were plotted we used a linear fit, and from this linear fit we obtained the slope of the plot,which tells us the coefficient of kinetic friction, which in this case is 0.3096
For part three of the experiment we just calculate the angle at which the block would start sliding and found out that the angle is 27 degrees from the horizontal.
For part four the procedure was the same the only thing that changed was that a motion sensor was used to find the acceleration of the block as it was sliding down.
Once this acceleration is found one can proceed and calculate the coefficient of kinetic friction
Using the data collected from the previous parts, one was able to predict the acceleration for the system, which it came out to be 2.267 m/s^2 Theoretical acceleration. The experimental acceleration came out to be 2.311 and it was found using the motion sensor which recorded the position and velocity as a function of time on logger pro.
Conclusion: The prediction of the acceleration of the two mass system using the data collected trough the experiments was not as accurate as one would have liked to have it due that there are parts for this particular experiment where the sources of error are very big. For instance, the first experiment is not consistent, which means that it is almost impossible to collect similar data twice. Another source of error for this particular lab comes from the second part of the experiment were the force is basically changing every second because it is really hard to pull the car at the same speed all the time, which affects the theoretical calculations for the acceleration of the system. The percent error between the theoretical and experimental values was calculated and it came out to be 1.9408 %, which lets one infer that is not accurate enough due to the sources of error described previously.
No comments:
Post a Comment