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Confused - How do I find the static and kinetic friction coefficient?

  • Thread starter Lida
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  • #1
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My physics prof's father died last week, and rather than cancel class, a different prof taught our class (by different, I mean a different one each day). This assignment was emailed to us by the head of the physics department, who spent less than five minutes with the class, and did not explain the lab that she assigned. Therefore, I'm doing a take home lab on friction, and need a few answers to complete it. Here are the instructions.

"The static coefficient of friction between two surfaces, υs, is equal to the friction force required to get the object moving divided by the object's weight. The kinetic coefficient of friction, uk, is equal to the force required to keep the object moving at the same velocity divided by the object's weight. Both coefficients are thus unitless and less than one. Using the force probe provided, measure the coefficient of static friction and the coefficient of kinetic friction between an object of your choice and five different surfaces. To do a good job, you will want to zero the probe, figure out a way to connect your object to the probe, and conduct multiple trials and average. All of the probes measure forces in "Newtons" or "grams". Read "Newtons". We ought never measure forces in "grams"."

I already did all the data collecting; here's one set:
I used my makeup case, weighing 1800g, or 17.5N, and hooked the probe to the handle on the top. On my linoleum floor, the average static force reading from the probe was 9.5N.

(I've attached a pic of my case on the linoleum floor)




From what the instructions say, static coefficient= force/weight and kinetic coefficient= force/weight.




My questions are:
1. is the reading from the probe my answer, or should I plug it into the equation like this? Static=9.5N/17.5N etc.

and

2. Should I give the weight of my case in Newtons or grams?

Thanks!
 

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  • #2
Doc Al
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My questions are:
1. is the reading from the probe my answer, or should I plug it into the equation like this? Static=9.5N/17.5N etc.
The probe gives you the force (in Newtons); to get the coefficient you need to use force/weight (like you did).

2. Should I give the weight of my case in Newtons or grams?
Weight is a force, so it should be in Newtons. (Grams is a measure of mass, not weight.)
 
  • #3
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Thanks!
 

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