18 September 2014: Friction Forces Lab 7

Objectives:
1) To use our understanding of friction to calculate either the static friction or the kinetic friction of a system

Part 1:
Materials:
1) 1 wooden block with felt on one side
2) String
3) Frictionless pulley wheel
4) 1 Styrofoam cup
5) water

Set up:

As you can see from this picture, we have clamped the pulley wheel to the table. We then placed the block with the felt side against the table and tied a string from the block, over the pulley wheel, to a cup which lies hanging over the table. We will then slowly add water to the cup.














Procedure:
First we must measure the mass of the cup without water in it. Our cup had a mass of .030 kg

Then we had to measure the mass of the block. Next we had to patiently add water to the cup until the block started to move. Once the cup had moved we had to record the mass of the water and cup. Then we repeated the experiment except we added more and more blocks to the first and recorded the mass of the added blocks.

3 blocks

2 blocks

We continued adding blocks until we had 4 blocks in total tied to the cup. The data that resulted from each trial can be seen below:

table 1

As seen from the table, we were able to calculate the normal force between the block and the table (column 3 of table 1). We did this by multiplying the total mass of the blocks x "g". We were also able to calculate the max static friction force between the block and table (column 4 of table 1). We were able to do this by multiplying the mass of the water and cup x "g". In both these calculations "g" = 9.81 m/(s^2)

We then wanted to plot our data. So we created a graph of the normal force between the block and the table (column 3 of table 1) and the maximum static force between the block and the table (column 4 of table 2). The resultant table could be seen below:

As you can see, we have added a trend line to the data. The slope that occurred from the graph was 0.3957. This was our coefficient of static friction.

So our coefficient of static friction was 0.3957.

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Part 2:

Materials:
1) 1 Block with felt on one side
2) String
3) Force Sensor
4) Logger Pro

Set up:

We have placed the block with the felt side against the table and have tied a string to the force sensor. Someone was then supposed to slowly pull the force sensor horizontally.

















Procedure:
First we had to calibrate the force sensor using a known mass. Then we recorded the mass of the wooden block. We then held the force sensor horizontally, started collecting data on Logger Pro, and started pulling the force sensor slowly moving the block at a constant speed. We then recorded the mass of additional blocks and repeated the procedure until we had a total of 4 blocks. The graphs produced by Logger Pro of these trials can be seen below:

From these graphs, we could collect the mean Force from the most flat part of the graph. The mean force represents the force at which the block was moving at a constant speed.

The data acquired from this lab was organized into the following table:

Table 2

The normal force between the blocks and the table (column 3 of Table 2) was calculated by multiplying the total mass of the blocks (columne 2 of Table 2) x "g". For our calculations "g"= 9.81 m/(s^2).

We again decided to create a graph from our data by plotting Normal Force (column 3 of Table 2) vs Kinetic Friction Force (column 4 of Table 2). The resultant table looked like this:

We again added a trend line to the data The slope that occurred from the graph was 0.3763. This was our coefficient of kinetic friction.

So our coefficient of kinetic friction= 0.3763

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Part 3:
Materials:
1) Ring stand
2) Clamps
3) A smooth track
4) Block
5) Device to measure angles
6)Logger Pro

Set up:

The track has been propped up with help of the ring stand to the point where the block is just about to slide. The bottom part of the track is held in place with a clamp.





Procedure:
First we had to measure the angle made with the track and the table. The angle was found to be 30.5 degrees.

We were then asked to calculate the coefficient of static friction. The calculations can be seen below:

u_s=0.589

For the next part we were asked to find the coefficient of kinetic friction. To do this, we raised the track so that the block slides down the track. We measured the angle at which the block slides down the ramp and found it to be 36.5 degrees. Then using the motion detection and Logger Pro, we recorded the acceleration of the black as it traveled down the track. With this data and the mass of our block, we were able to solve for the coefficient of kinetic friction. The calculations can be seen below:

u_k = 0.852

Conclusions:
From this lab we learned how to calculate static friction and kinetic friction. Unfortunately for part 1 the mass of the cup has a large range of error as we were not very patient. This might have had negative results for our data.