The purpose of this lab is to observe and figure out the friction force and coefficient of static and kinetic friction between two objects. This is done with multiple experiments dragging a block(s) across a surface.
Experiment
The first part of the lab was to observe static frictional force between the block and the table. This is done by having a block with felt on one side and having it face down on the table while connected to a string which is ran trough a pulley that is in turned connected to a cup. The cup is then filled with water until the block just barely starts to move. Once the block has moved the cup is weighed to find the mass, the mass of the block is found as well and all of this is recorded into a table witch is used to help calculate the normal force and the static friction force. This is repeated with blocks stacked on top of each other until there are four blocks in total.
The static frictional force is then taken and graphed against the normal force because the graph given will be used to find the coefficient of static friction between the felt under the block and the table. This is done by proportional fitting which would give us an equation of the line fs = AN which is similar to fs=μsN, meaning that the A is our coefficient of static friction.
The second part of this lab is to show the kinetic friction found between the block and the table. This experiment is set up with the same blocks used prior but this time with a force probe attached to other end of the string instead of a cup. Also instead of having the sting run through the pulley and have a weight to pull the block, the force probe is instead pulled at a constant pace to move the block at a constant pace. The force probe is also hooked up to the lap top and records the forces it is reading into logger pro. This is done repeatedly like prior with blocks stacking one on top another until there are four blocks.
Then from the graph produced by logger pro by using the statistic option in the area highlighted that was determined to be where the force was constant, it gives the mean of the forces in that region which is the average kinetic friction force acting against the block.
The mean kinetic frictional force is then taken and graphed against the normal force because the graph will be used to find the coefficient of kinetic friction between the felt under the block and the table. We then linear fit the graph and from the equation given the slope of the graph between the kinetic mean friction force and the normal force is the coefficient of kinetic friction.
The third part of this experiment was set up using a track, ring stand and motion sensor like seen below. For this set up the ramp has to be set at an angle where the block barely moves and then enough that the block would slide down it by itself. The purpose of this part is to find the coefficient of static and kinetic friction between the block and tack.
When the block just barely moves that is where the max static friction of the block is reached. From there the angle of the ramp is taken and the coefficient of static friction is calculated. In the calculation only the angle is needed because the mass and force of gravity cancel out. This is because the static friction is the force that keeps an object at rest therefore the weight of the block and normal force cancel out.
Now in a similar set up as before but at a steeper slope by letting go of the block and letting it slide, the motion detector picks up and records the data into logger pro creating a velocity vs time graph. The part of the graph that shows a constant velocity is once again taken and linear fitted. From the equation the fit gives the slope will be the acceleration of the block which will be used to calculate the coefficient of kinetic friction. The calculations for the kinetic friction is above next to the static friction.
In the last part of this experiment the block on the track flat with no incline and is tied to a string with a hanging mass at one end. Once the mass is released the block will move across the ramp and the motion detector will generate a graph from the blocks movement. This part of the experiment is used to see how accurate our coefficient of kinetic friction is in the prior part.
Before we analyze the graph the theoretical acceleration was calculated by using the kinetic friction found between the block and the ramp and angle in the prior part.
From the graph we can see that we were not far off from the theoretical meaning that these experiments are a good way to find he coefficients of kinetic and static friction. The errors that could have affected this experiment would be the track being dirty and not allowing the block to slide as smoothly. Another would be that the felt under the block was getting worn out and this slowing down the block not giving us accurate data.
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