- #1
reza
- 26
- 0
why coefficient of friction is less than 1?
dose it have a phisical answer
dose it have a phisical answer
Why coefficient of friction is less than 1
- Context: High School
- Thread starter reza
- Start date
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Discussion Overview
The discussion centers around the question of why the coefficient of friction (COF) is typically less than 1, exploring its physical implications and dependencies. Participants examine factors influencing COF, including surface characteristics and material properties, while also addressing misconceptions about friction coefficients.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants question whether the coefficient of friction can be greater than 1, suggesting that it might have a physical explanation.
- Others propose that the COF depends on the surface roughness of the materials involved, noting that highly polished surfaces can exhibit unexpected friction behaviors.
- A participant mentions that a coefficient of 1 is often considered perfect, implying frictionless interaction, but this is challenged by another participant who points out that this would actually correspond to a coefficient of 0.
- One participant models surface interactions using a pyramid analogy, suggesting that the angle of the pyramid's base relates to the friction coefficient, with most materials exhibiting a COF less than or approximately equal to 1.
- Another participant claims that a COF greater than 1 implies less force is needed to lift an object than to slide it, which raises questions about the interpretation of friction in different contexts.
Areas of Agreement / Disagreement
Participants express differing views on the nature of the coefficient of friction, with some asserting it can exceed 1 while others maintain it is typically less than 1. The discussion remains unresolved regarding the implications of a COF greater than 1 and the conditions under which it may occur.
Contextual Notes
Participants reference various sources and models to support their claims, indicating a reliance on empirical data and theoretical frameworks that may not be universally accepted. The discussion includes assumptions about surface interactions and the definitions of friction coefficients that are not fully clarified.
- #2
Gyroscope
No, it is not.
- #3
reza
- 26
- 0
then what is the coefficient of friction depends on
- #4
FredGarvin
Science Advisor
- 5,097
- 10
To an extent, the COF depends on surface roughness of the mating materials. However, you can get to a point where highly polished surfaces exert more friction than would be expected. You see that in some high speed seals and lapped surfaces in hydraulics.
The range of COF can span both >1 and <1. Here are a couple of references:
http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm
http://en.wikipedia.org/wiki/Friction
http://www.school-for-champions.com/science/frictioncoeff.htm
If you do a google search, there are tons of references.
The range of COF can span both >1 and <1. Here are a couple of references:
http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm
http://en.wikipedia.org/wiki/Friction
http://www.school-for-champions.com/science/frictioncoeff.htm
If you do a google search, there are tons of references.
- #5
reza
- 26
- 0
thank you very much
- #6
engineroom
- 29
- 0
A cooefficent of 1 is considered perfect and the mating surfaces are hence frictionless. If an object was pushed across a surface with a coefficient of 1 then the object would continue to slide forever.
Any cooefficent is always unitless.
Any cooefficent is always unitless.
- #7
C4guy
- 2
- 0
Hi!
Errr... That would be a friction coefficient of 0.
c4guy
engineroom said:
Errr... That would be a friction coefficient of 0.
c4guy
- #8
reza
- 26
- 0
if (coefficient of friction)=1 we can say just f=N.(COF) => f=N and some times f=m.g
- #9
pixel01
- 688
- 1
When you magnify the surface of the objects, it is surely not completely flat, but rough. From that viewpoint, I model it like pyramids (see picture). So with the model you can calculate the friction coefition. If the angular of the pyramid (at bottom) equals 45 degree, the coefition is 1.
It is easy to see that it's very difficult for a pyramid with bottom angular of more than 45 degrees. That's why as you can chech in the friction table, most of the materials have the friction coefficient of lower than 1 or approx. to 1. Of course this depends on the crystal structure of the material.
The friction I mention above is the dynamic, not the static one. For static friction, there may be some more force linked with the adsorption force or else..
It is easy to see that it's very difficult for a pyramid with bottom angular of more than 45 degrees. That's why as you can chech in the friction table, most of the materials have the friction coefficient of lower than 1 or approx. to 1. Of course this depends on the crystal structure of the material.
The friction I mention above is the dynamic, not the static one. For static friction, there may be some more force linked with the adsorption force or else..
Attachments
- #10
DyslexicHobo
- 249
- 0
With a coefficient of friction greater than 1, you can assume that it requires less force to lift the object from the ground, rather than slide it across a surface.
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