Sept-18-2014 Determining kinetic friction coefficient

Kinetic Friction

Purpose:

Students conducted an experiment to determine the kinetic friction coefficient between a block and a table.

 Lab:

The lab was accomplished using string, block(s), and a force sensor. It was setup in this way:

The block was connected to the force sensor through the string which would allow the students to record the force necessary to pull the block.

The students first had to zero the block through logger pro to minimize error in data collection. The students then measured the mass of the block and recorded it and then pulled the force sensor at a constant velocity to record the force necessary to move the block.

The force was displayed through a graph: 

The slope of the velocity vs time graph was determined to be the average kinetic friction force.

The experiment was repeated five times with a block added each time. The mass of the blocks and the average force from the force sensor was recorded each time into a table:

The students then used the data to plot a graph of Normal force vs Kinetic friction force and as explained in the static friction lab, the slope of this graph would theoretically be the kinetic friction coefficient.

Graph:

Conclusion:

The students were able to determine a kinetic friction coefficient through hands on lab experience. The kinetic friction coefficient was determined to be 0.2887 from the lab.

Sept-18-2014 Determining Static Friction

Purpose:

Students will use an experiment to determine the static friction coefficient of an object.

Lab:

The students assembled a lab setup that would allow them to measure the static friction coefficient of an object with a table. The accomplished this with a pulley, string, a cup, and a wooden block with felt on one side.

The mass that will be used to determine the static friction coefficient is the wooden block so the mass of the block was measured so that the students would be able to calculate the normal force that the table would have on the block.

Then the components are assembled as shown:

The block is placed on the table with the felt side down and a string is tied to it. the string is then looped on a frictionless*, massless* pulley and the other end is tied to a cup. 

Once the setup is complete the students then took the following steps. They added water to the cup until just the point when the block would start moving. They then measured the mass of the cup and water. The students repeated these steps five times. Each time with an added block to increase the mass and therefore the Normal and ultimately the frictional force the block would have with the table.

The Mass of the block(s), the mass of the water+cup, and the Normal force between the table and the block was recorded and kept track of in a table:

The students then determined that the max static friction force was equal* to gravity x the mass of the water&cup. Also, friction force equals the coefficient of friction x N. 

Therefore in order to find the static friction coefficient, students plotted the graph of Normal force versus the max static friction force. Since slope is y/x, in this case it would be Normal force/ max friction force which would theoretically yield the max static friction coefficient.

The Graph:

The graph displayed a slope of .3865 which the students took to be the max static friction coefficient.

Sept-16-2014 Calculating mass of object

Purpose:
Students calculated the mass of an object by measuring the force needed to hold the object in place.

Lab:

The lab came pre-set up as shown:

A string which held up an object is tied to two force measures that record the force needed to hold up the object.

The students first had to reset the force measures to zero to try to reduce error as much as possible. The students then attached the object to the string and let gravity pull the object down and the strings hold them up.

The students then recorded two key pieces of data from the experiment: the force being recorded on the force measures and the angle of the two parts of the string.

With these two pieces of data students then calculated the mass of the object.

Mass calculation:

Students then accounted for the error in the data with a data analysis by taking into account the a possible angle error of 2 degrees because of the angle measure and human error and the possible error of 0.5 newtons because of the inaccuracy of the force measures.

Error Analysis:

Conclusion:

Students successfully calculated the mass of an object with the use of force measures and string.

Sept-16-2014 Calculating Density and Error Analysis on Aluminum, Copper and Steel

Purpose:

This lab will teach students to perform error analysis on data gathered from experiments.

Lab:

Students were given three cylinders of different materials: Aluminum, Steel and Copper.

Students then used a caliper and mass scale to record the height, diameter and mass of the three cylinders.

A simple volume calculation was done to find volume and with the mass and the volume the students calculated the density of the cylinders with the equation d = m/v.  All of the data was written onto a whiteboard.

Then an error analysis was performed by taking into account the error of the mass scale which had an error of .01 grams and the caliper which had an error of .01 cm

The calculated density for the three materials aluminum, copper and steel along with their respected calculated errors were then compared with the textbook densities for the materials and it was found that the textbook densities were within the student's calculated error range.

Conclusion:

The students successfully calculated the density of the three materials with an error range that met the established 'actual' densities of the three materials.