To learn more about measuring various frictional forces.
This lab included 5 parts (a through e), with all parts purposed to help us understand friction.
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a) Static friction with cup and water
We began the first part by setting up our apparatus, which included a felt-bottom-block resting on the table surface tied to a string (I will reference this as end A). Between both ends of the string was a pulley/wheel which was secured to the edge of the table. We let the string pass through the pulley and hang off the edge of the table - at this hanging end(end B), we tied a foam cup.
Our task for Part A was to measure the coefficient of static friction.
The process looked like this:
- Weigh the mass of the block(s) tied to End A of the string.
- Gradually fill the foam cup, at End B, with water until the block(s) resting on the table, begin moving. (Note: This point represents the value for the max. static friction)
- Weigh the mass of the cup, with the water still in it.
- Stack another block on top of the block which is tied to End A of the string.
- Repeat all previous steps.
We repeated the experiment, adding one block to the system with each repeat until we had, at one point, four blocks stacked.
Solving for the coefficient of the maximum static friction,
The values we calculated as a group were as follows:
We then plotted the data on a graph with a linear fit, however, before graphing we told the computer to graph without the fourth data point. We noticed during our calculations that something went wrong with the fourth piece, so we ignore it.
We made a plot of the Maximum Static friction force on the y-axis vs. Normal force on the x-axis.
This gave us the average coefficient for kinetic friction (slope) - which turned out to be about 0.39.
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b) kinetic friction with force sensor
For the second part, we needed to find the coefficient of kinetic friction.
Our apparatus for this part was simply a block (mass) tied to a force sensor, which we pulled at a constant velocity (roughly).
This allowed us to find the coefficient of friction using the force recorded on the force sensor, the mass of the block and using the known value of gravity.
Similar to part A, we measured four values (stacked multiple blocks).
To the best of our ability, we pulled a block at constant speed and got a measurement for the Tension force of each of the four measurements.
We then plotted the data from the four measurements on a Force-of-Pull-Vs.-Normal-Force graph.*
Analyzing this new graph, we found that the slope gave us the value for the coefficient of kinetic friction.
*Our graph went missing and our actual values for the forces were lost with the graph.
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c) static friction from angle to get sliding
For the third apparatus we had an incline/ramp and a felt-bottom-block.
The plan was simply to increase the angle under the incline until the block began to move.
This value for theta would help us find the coefficient for static friction between the block and the ramp.
We measured an angle of 20 degrees for the incline just as the block began moving.
We found that the coefficient of static friction between the block and the ramp was 0.36, noting that for this particular set-up, the only information we needed was the angle of the ramp.
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d) kinetic friction from sliding block on a steep ramp
For the fourth part of the activity, we used the same apparatus from part three. The difference in this new apparatus was an attached position sensor, at the top of the ramp.
Our goal for this part was to measure the coefficient for kinetic friction between the block and the ramp. We increased the angle of the incline to 30 degrees so that the block would accelerate down the incline, away from the sensor.
The acceleration of the block that we recorded through the sensor turned out to be 0.896m/s^2 and was in the direction parallel to the ramp.
The coefficient for kinetic friction between the block and the ramp was calculated as 0.47.
e) predicting acceleration of a two-mass system—one on a friction ramp, the other hanging.
We performed the fifth part of the activity using the same apparatus as we did in part 4. The difference this time was that we moved the position sensor from the top of the ramp to the bottom - we also attached the pulley/wheel (from part 1) to the top of the ramp and hung a 500 gram mass, which was connected by a string to the 143 gram block on the ramp.
When we began part 5, we released the hanging mass from a reasonable height and collected the acceleration data through the sensor. The block was moving upward and parallel to the ramp.
Before we examined the sensor's value for the acceleration, we made a prediction for the acceleration using the known value for the coefficient of kinetic friction (0.47), the angle under the ramp(30 degrees), and the known values for each mass.
Our prediction for the acceleration of the block going up the ramp was calculated as 3.15 m/s^2.
We then plotted the sensor's collection data on a position-vs-time graph and a velocity-vs-time graph.
Specifically focused on the part of the graph with an increasing velocity, we were able to find an acceleration from the slope of the velocity-vs-time graph.
However, our graph (pictured above) may have contained some faulty data, or some unaccounted errors - we know this to be true because of the unreasonable value for slope (acceleration) which was 130.5 m/s^2.
A great day for Physics.
(9/15/14 7am)
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