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jhk0428
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I don't understand what determines the coefficient of friction. Can someone explain it to me using examples?
What determines the coefficient of friction?
- Thread starter jhk0428
- Start date
In summary, the coefficient of friction is determined by the materials of the object and surface, as well as other factors such as surface impurities and roughness. Local bonding and surface interlock also play a role in friction. This phenomenon can even be observed at home with glass on glass. Overall, understanding the coefficient of friction requires knowledge of tribology and its various components.
- #2
Whovian
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What the coefficients of friction depend on are the materials the object and the surface it's sliding over are made of.
- #3
Studiot
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Look at my post#9 in this thread
https://www.physicsforums.com/showthread.php?t=437463&highlight=friction
https://www.physicsforums.com/showthread.php?t=437463&highlight=friction
- #4
Vargo
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The coefficient depends on the two materials and especially on the impurities on their surfaces. For example take copper and copper. "Clean and dry" 1.21. Thick oxide film .76. Sulfide film .74. These values serve to illustrate how variable the coefficient can be. If you cleaned the copper perfectly and stuck the two surfaces together in a vacuum, you would get a huge coefficient because essentially the two pieces fuse together into one continuous copper piece.
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Studiot
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Vargo, it would be worth expanding upon coefficients greater than unity since this implies a greater force required to slide the object than to simply lift it off the other surface and move it along, supporting it in thin air.
- #6
Vargo
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Good point Studiot. But consider rubber on rubber. Doesn't it seem plausible that picking up the rubber and moving it through the air would be less work? Check out
http://www.engineershandbook.com/Tables/frictioncoefficients.htm for other particular examples.
I don't know a lot about this personally, but I can try to faithfully paraphrase R. Feynman in "Lectures on Physics". If you have two surfaces of the same pure substance such as copper and you are somehow able to eliminate all impurities separating them, then they can bond together and form a continuous metal piece. Apparently this can be observed at home with glass on glass. If you put a bit of water between the surfaces it can lift the impurities out of the way and allow the two pieces of glass to bond together in places. If you then slide one along the other, you will notice nicks in the glass where the two pieces of glass were ripped apart.
I don't know how this phenomenon would affect the coefficient of friction between two different materials like copper and steel, but it at least serves to illustrate the tricky nature of the coefficient and its dependence on "hidden variables" such as surface impurities that could vary depending on the exact situation.
http://www.engineershandbook.com/Tables/frictioncoefficients.htm for other particular examples.
I don't know a lot about this personally, but I can try to faithfully paraphrase R. Feynman in "Lectures on Physics". If you have two surfaces of the same pure substance such as copper and you are somehow able to eliminate all impurities separating them, then they can bond together and form a continuous metal piece. Apparently this can be observed at home with glass on glass. If you put a bit of water between the surfaces it can lift the impurities out of the way and allow the two pieces of glass to bond together in places. If you then slide one along the other, you will notice nicks in the glass where the two pieces of glass were ripped apart.
I don't know how this phenomenon would affect the coefficient of friction between two different materials like copper and steel, but it at least serves to illustrate the tricky nature of the coefficient and its dependence on "hidden variables" such as surface impurities that could vary depending on the exact situation.
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Studiot
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Pity because I thought I was offering you a cue.
Local bonding or fusion between the two surfaces is one aspect of friction.
Another is the degree of surface roughness, which allows some mechanical interlock to increase friction.
Reducing such interlock is also the main part of the mechanism of lubricants in reducing friction.
The science of surface contacts is known as Tribology.
FAQ: What determines the coefficient of friction?
What is the coefficient of friction?
The coefficient of friction is a measure of the amount of resistance between two surfaces in contact with each other. It is a dimensionless number that ranges from 0 to 1, with lower values indicating less friction and higher values indicating more friction.
What factors determine the coefficient of friction?
The coefficient of friction is determined by several factors, including the nature of the two 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 friction tester or a tribometer. These instruments apply a known force to the two surfaces and measure the amount of friction that occurs.
Why is the coefficient of friction important?
The coefficient of friction is an important concept in physics and engineering as it helps us understand and predict how objects will interact and move across surfaces. It is also crucial in the design of machines and structures to ensure proper functioning and safety.
Can the coefficient of friction be changed?
Yes, the coefficient of friction can be changed by altering the factors that determine it. For example, using a lubricant between two surfaces can reduce the coefficient of friction, while increasing the roughness of the surfaces can increase it.