# Differences in kinetic friction coefficents

• jmcmillian
In summary, the speaker conducted an experiment to determine the coefficient of kinetic friction for a wooden block and weight using two methods. The results from the two methods showed a difference of .07 in the coefficient of friction. The speaker ruled out any anomalies and was seeking an explanation for this difference. Another individual suggested that the slight angle in pulling the block may have affected the normal force and resulted in a different coefficient of friction. The speaker was advised to calculate the angle to determine its plausibility.
jmcmillian
Is a difference in .07 when it comes to coefficients of kinetic friction for the same object on the same surface significant? I thought it was, but I have yet to determine a reason why. Below is an explanation of my experiment, as brief as possible.

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I ran an experiment in which I had a wooden block and a weight.

My objective was to determine the coefficient of kinetic friction for the block and the weight.

I did this using two methods: One in which the block+weight was tied to a sensor box, which was connected through an interface to software. As I diligently pulled the sensor box, the block+weight would move (overcoming static friction) and then both units would slide across the table as I pulled, only facing kinetic friction. I did this four times, and received similar results on each.

The other method I used was with a motion detector apparatus. I took the block+weight and simply gave it a shove towards the detector. I did this five times, and saw similar results.

Now my problem is that my coefficient of kinetic friction for the push is on average .07 more than my value for the pull.

My first attempt to rationalize this is that the force I applied in the shove (push) was much greater than the force for the pull, but I then reasoned that it shouldn't really affect the kinetic friction coefficient, only the static value.

I ruled out a anomaly in the average of each because the results were precise...
< .02 or less difference in each of the 5 trials on the push experiment
< .03 or less difference in each of the 4 trials on the pull experiment.

Any ideas on how to explain this?

Are you pulling the block absolutely horizontally? You may have some force going into lifting or pushing the block down which would cause your normal force to be less/greater than what you calculated, resulting in a different coefficient of friction.

hunter151 said:
Are you pulling the block absolutely horizontally? You may have some force going into lifting or pushing the block down which would cause your normal force to be less/greater than what you calculated, resulting in a different coefficient of friction.

hunter, Thanks for the advice. There might have been a slight angle to me holding the rope, resulting in the difference.

Try calculating the angle you would have to make to account for the difference in the the coefficients and see if this is a plausable angle.

## 1. What is kinetic friction coefficient?

Kinetic friction coefficient is a measure of the amount of friction between two surfaces in motion against each other. It represents the ratio of the force required to keep an object moving at a constant velocity to the perpendicular force between the two surfaces.

## 2. How is the kinetic friction coefficient different from the static friction coefficient?

The kinetic friction coefficient is generally lower than the static friction coefficient. This is because once an object is in motion, it requires less force to keep it moving than it does to overcome the initial resistance to motion when the object is at rest.

## 3. What factors affect the kinetic friction coefficient?

The kinetic friction coefficient can be affected by various factors such as the nature of the surfaces in contact, the roughness of the surfaces, the temperature, and the presence of any lubricants or contaminants.

## 4. How can the kinetic friction coefficient be measured?

The kinetic friction coefficient can be measured by conducting experiments where the force required to keep an object moving at a constant velocity is measured and compared to the perpendicular force between the surfaces. It can also be calculated using mathematical equations.

## 5. What are some real-world applications of understanding differences in kinetic friction coefficients?

Understanding differences in kinetic friction coefficients is important in various industries such as transportation, manufacturing, and sports. It can help in designing more efficient vehicles and machines, reducing wear and tear on surfaces, and improving athletic performance by selecting the right materials and surface textures.

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