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

In summary, the physics professor's father passed away, so another professor taught the class and assigned a take-home lab on friction. The instructions state that the static coefficient of friction (force required to get an object moving) and kinetic coefficient of friction (force required to keep an object moving) are both unitless and less than one. The lab requires measuring these coefficients between an object and five different surfaces using a force probe. The weight of the object should be in Newtons, not grams. The probe gives the force, which needs to be divided by the weight to get the coefficient.
  • #1
Lida
10
0
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
Lida said:
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
Thanks!
 

1. What is the difference between static and kinetic friction?

Static friction is the force that prevents an object from moving when a force is applied to it, while kinetic friction is the force that opposes the motion of an object that is already in motion.

2. How do I measure the static and kinetic friction coefficients?

The static friction coefficient can be measured by gradually increasing the force applied to an object until it begins to move, while the kinetic friction coefficient can be measured by measuring the force required to keep an object in motion at a constant speed.

3. What factors affect the static and kinetic friction coefficients?

The static and kinetic friction coefficients can be affected by the materials of the two surfaces in contact, the weight of the object, and the roughness of the surfaces.

4. Can the static and kinetic friction coefficients be different for the same two surfaces?

Yes, the static and kinetic friction coefficients can be different for the same two surfaces. This is because the surfaces may have different levels of roughness or other factors that can affect the friction coefficients.

5. How can the static and kinetic friction coefficients be used in real-world applications?

The static and kinetic friction coefficients are important in various engineering and design applications, such as determining the maximum weight an object can hold on a surface, designing brakes for vehicles, and creating anti-slip materials.

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