Are Coefficients of Friction Independent of Weight?

In summary, coefficients of friction (µs and µk) are independent of the weight being pulled, as seen in PF Library on friction and other reliable sources. Although the pressure may affect the coefficient, it is directly proportional to the weight, so the coefficients will stay the same regardless of the weight. It is still recommended to do trials to determine the coefficient for specific applications.
  • #1
mybrohshi5
365
0
Are coefficients of friction Ms and Mk independent of the weight being pulled?

We just had a lab on friction and i am just curious about this.

Thank you
 
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  • #2
Hi mybrohshi5! :smile:

(have a mu: µ :wink:)

In examination questions, µs and µk are always independent of weight. :wink:

In reality, see this, from the PF Library on friction:

Tables of coefficients of friction:

Many tables can be found on a http://www.google.com/search?client...ficients+of+friction+table&ie=UTF-8&oe=UTF-8", which begins
"Extreme care is needed in using friction coefficients, and additional independent references should be used. For any specific application the ideal method of determining the coefficient of friction is by trials. A short table is included above the main table to illustrate how the coefficient of friction is affected by surface films. When a metal surface is perfectly clean in a vacuum, the friction is much higher than the normal accepted value and seizure can easily occur."
For some materials, the coefficient can be greater than one, and for solids on rubber it can be as high as four.

Increasing pressure between dry surfaces may increase the coefficient, at first slightly, but eventually very quickly, leading to seizing. For this and other factors affecting coefficients of friction, see the top box in http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm" [Broken]
 
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  • #3
Thanks tiny-tim.

In my lab we used about a 1 kg weight on top of a wooden block and that was dragged across the table.

So say i reduced that weight down to 0.5 kg and dragged it again would the coefficients of friction be the same or different?

From what i got from the websites you posted i think the coefficients of friction will be independent of the weight therefore making them stay the same because...

...since relatively low pressures are being used then the friction would go down as the weight goes down and the friction would go up as the weight goes up (to an extent) so basically i am saying that the friction is directly proportional to the weight so µk and µs will stay the same making them independent of the weight being pulled...
 
  • #4
Hi mybrohshi5! :smile:

Should be the same, for exactly the reasons you've given.

(But you should still try it! :wink:)
 
  • #5
Thank you. That helped clear up a lot of things for me :)
 

What is a coefficient of friction?

A coefficient of friction is a dimensionless quantity that represents the amount of resistance or friction between two surfaces in contact with each other. It is a ratio of the force required to move one surface over the other to the normal force between the two surfaces.

What factors affect the coefficient of friction?

The coefficient of friction is affected by several factors, including the nature of the surfaces in contact, the roughness of the surfaces, the force pressing the surfaces together, and the presence of any lubricants or contaminants.

How is the coefficient of friction measured?

The coefficient of friction can be measured using a variety of methods, including a coefficient of friction tester, a tribometer, or by conducting experiments in which the force required to move one surface over the other is measured and compared to the normal force.

Why is the coefficient of friction important?

The coefficient of friction is important in many fields, including engineering, physics, and materials science. It helps us understand how two surfaces will interact with each other, and it is crucial in designing and predicting the performance of various mechanical systems.

What are some real-world applications of the coefficient of friction?

The coefficient of friction is used in a variety of real-world applications, such as determining the traction of tires on different road surfaces, designing brakes for vehicles, and predicting the performance of bearings and other mechanical systems. It is also important in sports, such as determining the grip of shoes on different playing surfaces.

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