Maximum coefficient of friction

In summary, the conversation discusses the question of whether a coefficient of friction (static) can be larger than one. Various examples are given, such as the coefficient of friction of glue, table tennis rubber, and metal on metal. It is concluded that a coefficient of friction can indeed be larger than one, as seen with table tennis rubber sheets having a coefficient of friction of 5.0+. Other examples, such as race car tires and dragster tires, also achieve coefficients of friction above 1.
  • #1
FranzDiCoccio
342
41
This issue was the subject of this old post, now closed.
The question is: can a coefficient of friction (static) be larger than one?

I see confusing replies. Someone talks about glue, but I'm not convinced about that. It's a bit like wondering about the coefficient of friction of a wooden plank nailed to a wall.

I like the "micro hills" explanation by pixel01, and the table tennis video by rcgldr.
Actually, whenever something won't slide down a plane inclined at an angle larger than 45° it should be
[itex]\mu_s>1[/itex], right?
However I'm not sure about the table tennis rubber. To what extent the surface is really a plane? If it has grooves the object can hang onto those "mechanically" (I mean, at the macroscopic level).

Again, it is a bit like saying that the coefficient of friction between ice crampons and ice is very high.

I think that [itex]\mu_s[/itex] can be larger than one, but I'd like a more precise answer... I'm not sure there is one though. I guess that the surfaces one considers should not be too irregular, but I don't know whether a quantitative rule exists. When is a micro hill really micro? When it is small compared to the area of the sliding surfaces?

Thanks
 
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  • #2
FranzDiCoccio said:
The question is: can a coefficient of friction (static) be larger than one?
The answer is: yes.

It's just a ratio, not an efficiency or something that otherwise has a restriction on the numerical value.
 
  • #3
Thanks BvU
I agree with that, but I still find the comments about glue confusing.

Is there a rule of thumb for understanding when it is a matter of friction and when it's not?

Is the force keeping an object from sliding on a plane is still friction, if the object is glued to the plane or if the surfaces are very irregular (on a scale comparable with the object size)?
 
  • #4
I don't think it really works for glued/screwed etc contacts, since the formulaic implication of the coefficient is that the friction force is proportional to the normal force. That obviously is not the case for glue or screws. So you would be calculating a value with a formula that doesn't really apply.
 
  • #5
You're right!
Ok, what you're saying is that if I glue a block of balsa wood onto a plane, its resistance to sliding onto the plane has nothing to do with friction, which depends on the normal force, which is laughable for such a light material.

Cool, this definitely kills the glue argument, which, btw, never convinced me one bit.
I do not know why I did not think this myself, but really, thanks a lot!
 
  • #6
Table tennis racket rubber sheets have a coefficient of friction well above 1.0, more like 5.0+. Example windows movie video using a comb on a steeply angled racket until the comb slides off.

http://rcgldr.net/real/ttstick.wmv
 
  • #8
CWatters said:
some of the highest figures are for metal on metal.
Top fuel and funny car dragster tires achieve a coefficient of friction around 4.5. The initial launch is close to 5 g's, but the exhaust from the engine is adding significant downforce. Race car tires are achieve 1.5 up to well over 2.0 (Formula 1 super soft tires).

As I posted previously, high end table tennis rubber has a coefficient of friction well over 5.0 with table tennis balls or other types of plastic.
 

Related to Maximum coefficient of friction

What is the maximum coefficient of friction?

The maximum coefficient of friction is the highest possible value that can be achieved between two surfaces in contact. It is a measure of the resistance to motion between the two surfaces.

How is the maximum coefficient of friction determined?

The maximum coefficient of friction can be determined by conducting experiments using different surface materials and measuring the force required to move one surface over the other. The ratio of this force to the normal force between the surfaces gives the coefficient of friction.

What factors affect the maximum coefficient of friction?

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

Why is the maximum coefficient of friction important?

The maximum coefficient of friction is important in many real-world applications, such as designing tires for vehicles, determining the stability of structures, and improving the performance of machinery. It also helps in understanding the limitations and capabilities of different materials.

Can the maximum coefficient of friction be greater than 1?

Yes, the maximum coefficient of friction can be greater than 1 in certain situations, such as when two rough surfaces are pressed together with a significant amount of force. However, in most cases, the maximum coefficient of friction is less than 1. A value of 1 would indicate that the two surfaces have equal resistance to motion, which is not common in most materials.

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