Lab 4/8: Frictional Force

 Lab 4/8: Frictional Force

Purpose

The purpose of this assignment was to experimentally determine the coefficient of friction by plotting a frictional force vs. normal force graph.

Procedure

The mass of the cart and height of the track were varied while the time to travel 1 meter were collected experimentally according to the measurement plan. 4 trials with the same parameters were done to determine uncertainty. The frictional and normal force were calculated based on the experimental results and equations derived in class. Then, the values were plotted on a graph for further analysis.

Results

What is the coefficient of kinetic friction for wood on aluminum?  How does this compare to your prediction?

 The coefficient of kinetic friction for acacia wood on an aluminum track came out to be about 0.315. The relationship between these two forces is described by the equation: fk= μkN. So, when graphing a frictional force vs. normal force graph, the value of the slope should result in the coefficient of kinetic friction. This result fits nicely within our predicted range of 0.2 to 0.6, which we based on typical values for wood on metal. So getting 0.315 suggests the interaction between the acacia wood and aluminum was about what we expected—moderate friction, not too slippery but not overly sticky either. Overall, it shows that our method worked and our prediction was on point.

What are the limitations on the accuracy of your measurements and analysis?  Over what range of values does the measured graph match the predicted graph best?  Where do the two curves start to diverge from one another?  What does this tell you? 

There were limitations on the accuracy of our time measurements since they were recorded by hand. Holding the height constant while changing the mass of the block produced the most linear results. The lighter the mass of the block, the more the measured graph matched the predicted linear graph, specifically from 80- 100 grams. After the mass reaches 100 grams, the two curves begin to diverge from each other. This implies that there are some other factors that aren’t accounted for in the model that are amplified with larger masses as air drag.

Graph 1. Masses changing, heights constant                Graph 2. Heights changing, masses constant

Uncertainty was calculated to be 0.12 through Excel functions