Kevin Tran
Lab Partners: Kevin Nguyen, Jose Rodriguez
March 26, 2017

Friction Forces

Purpose: To find out how to find the static and kinetic friction of an object. Students performed several experiments in order to see what role friction plays on the object that is sliding over different types of surfaces.

Introduction/Theory: My lab partners and I have done 5 experiments to determine both static and kinetic frictions at certain cases. We calculated friction by using a two-mass system and by inclining a wooden board.

(1) 

First, we performed an experiment by using a two-mass system in order to help us determine the coefficient of static friction between the block and the table. (picture below). In order to do so, we use the equation

Coefficient of static friction = (maximum force of static friction)/ (normal force)

To find the coefficient of static friction, we need to find the maximum force of static friction and the normal force exerted on the object.

We chose two masses: a block(0.173kg) and a hanging mass(0.55kg).

During this experiment, we tested how much weight will be needed on the hanging mass in order to determine the static friction of the block. We have done 6 trials: block itself, block with 200g, block with 400g, block with 600g, block with 800g, and block with 1000g. With each trial, we continuously added weight onto the hanging mass until the block moves.

Overall, these are the trials for each mass of block and mass required to move the block in order to move.

With these results, we created a mass(x-block) and mass(y-hanging mass) graph on loggers pro in meters so that when we make a line fit of the plot, the slope gives us the coefficient of static force.

In this graph, we were able to find the slope of the graph, which also represents μs(static friction). The slope of the graph is 0.6025.

(2)

In the 2nd experiment, we were required the measure the coefficient of kinetic friction between the block and table. We use this equation to do so:

Coefficient of kinetic friction = (Force of kinetic friction)/ (Normal force on the object)

In the 2nd experiment, we were told to find the kinetic friction. To find kinetic friction, we had to move the block with a dual-range force sensor. Both of these objects will be connected to a string for more accuracy.

We have done 4 trials while performing this experiment. We used the following weights: block(0.173kg), block with 200g, block with 400g, and block with 600g. We set the force sensor on the 10-N range.

Since were pulling the block in a constant velocity, our acceleration will be 0m/s^2

We also have the data for the 4 trials. We used the mean value from the white boxes.

With this information, we were able to construct a weight and force(tension) graph. We took the mean value the of the pulling force in the interval when the block moved horizontally at constant speed. We plotted the average kinetic friction force. We used the 4 different masses for the x-axis(also our normal force) and force pulled on the x-axis and made a line fit of the plot in order to find the slope of the line, which will give us the coefficient of kinetic friction.

With this graph, we were able to find the slope of the coefficient of kinetic friction(Mu), which results in 0.2786.(slope)

Below is a closer look of the white box.

(3)
The 3rd experiment was to incline a wooden board to know what angle will make the block slide down. We used an angle app on our phones and taped it to the wooden board to get the angle.

In the end, the block starts to slide down the board when the board is at a incline of 26 degrees.

We also calculated in order to find static friction(Mu) of the surface at 26 degrees and we ended up getting 0.488.

(4)
Experiment 4 of the lab is similar to experiment 3 but this time, we are looking for kinetic friction when the block sliding down the incline at 26 degrees. When the block is sliding down, there is a motion detector at the top of the incline steep enough that a block will accelerate down the incline.

We have created a position/time graph and a velocity/time graph in order to find the acceleration of the block when it's accelerating. From the velocity/time graph, we were able to find the slope of when the block begins to accelerate. In the end, we end up getting 1.607 m/s^2.



We also found the kinetic friction of the surface as the block slides down. Our kinetic friction(Mu) value happens to be 0.295

(5)
Experiment 5 was to predict the acceleration of a two-mass system. We set up the apparatus similar to part 1 of the lab. Except we placed the motion sensor behind the object to record the acceleration for the block. We solved for the kinetic friction by setting the direction of acceleration of the block as the x-axis and set the y-axis perpendicular to the x-axis. We needed to solve for the vertical and horizontal forces in order to find the kinetic friction force and normal force. We apply the formula for kinetic friction by dividing the kinetic friction force by the normal force in order to find the coefficient of kinetic friction.

This is the set up for experiment 5. (picture below). The reasoning for the white tape that is connected to the block is because it makes the block to detect for the motion sensor when the block accelerates away from the motion detector.

Mass of block= 0.188 kg
Mass of hanging mass= 0.09 kg

For this experiment, we created a position/time graph and a velocity/time graph in order to give us the acceleration of the block when it is moving. From the velocity/time graph, we found that the acceleration of the two-mass system is 0.7627 m/s^2 from the slope.

Below, we have found the kinetic friction(Mu) of the two-mass system of 0.3704



Conclusion:
This lab allowed us to understand how static and kinetic friction works. The value of static Mu from experiment 1 is greater than the value from experiment 3. The difference between these results came up because the experiment 1 tends to be inconsistent. Even though the mass of the block remains the same, it falls with different masses added on the hanging mass. In the comparison to experiment 2 and 4, the value of kinetic Mu is close to each other but not exact. Also the value of kinetic Mu in experiment 2 is closer to experiment 4's result than experiment 5. Even though neither static Mu nor kinetic Mu values are similar, the results of experiment 1 and 3 were both greater than the results from experiments 2, 4, and 5, allowing the lab to be valid.