Modeling Friction Forces (Lab #7)

Ana Leyva, Andrew, Jonathan
3/22/17
The goal for this experiment was to be able to model static and kinetic friction by conducting different experiments. This will be done by using free body diagrams and applying Newton's laws.

1.) Static Friction
In order to find the static friction for this experiment we had to find out how much mass it would take to get a certain object to move. In order to set up for this experiment we first set a white piece of wood on the table that would provide us with a smooth surface. Then we put a pulley on the end of the table. We then attached a string to a block and to a hook that would allow us to place weight on top of it. We then set the block to a designated place on the table and started adding weight to the hook until we got the block to move. We then repeated this process three more times. Each time we added 100g to the block. After doing this we plotted a F_static vs. N graph that would allow us to get a coefficient of static friction. By using the free body diagram you can see that the weight that forces the block to move will be the static friction and the weight of the block will represent the normal force. We then graphed these values and got the following graph with gave us a coefficient of static friction = .3935

2. Kinetic Friction

For this part of the experiment we used a force sensor to find the average force that it takes for an object to keep on moving. We did this for all of the four different masses. Once we got the means for each run we made a F-kinetic vs Normal force graph. For this one we used the mean for each of the four graphs to represent F_kinetic and the mass of the block to represent the Normal force.

According to both of these graph the coefficient of kinetic friction is equal to 0.234

3. Static friction from a sloped surface

In order to find the static friction from a sloped surface we first lifted the board until the board started to slip. For this we got theta= 20.05 degrees. We then used the free body diagram to help us find what the coefficient of static friction would be. After solving for this we got coefficient of static friction = 0.365

4. Kinetic Friction From Sliding a Block Down An Incline

 For this experiment we set the board at a certain angle. We then put a block down on the board and let it slip down. Using a motion detector we calculated the acceleration of the block. By getting the value of the acceleration and the angle at which the block slipped we were then able to calculate the coefficient of kinetic friction. In this case the coefficient of static friction was 0.298.

5. Predicting the Acceleration of a Two-mass System
In order to predict the acceleration of a two-mass system we first had to go back to drawing a free body diagram. We then solved for A and plugged in all of our values.

 This was a very interesting experiment that allowed me to have a better understanding on how to solve for various thing. It also allowed be to see a correlation between everything.