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ItDoesn'tMatter
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I am aware that there needs to be two materials for there to be a coefficient of friction, but I mean in general. For example, I know synthetic setae are very resistant to slipping on surfaces.
The highest coefficients of static friction are for dry contact between identical metals.ItDoesn'tMatter said:I am aware that there needs to be two materials for there to be a coefficient of friction, but I mean in general.
That's interesting I did not know that about self stick of metalsBaluncore said:The highest coefficients of static friction are for dry contact between identical metals.
Examples of coefficients ≥ 1.00 are;
1.00 Iron — self
1.00 Copper — self
1.05 Copper — Cast iron
1.10 Cast iron — self
1.10 to 1.35 Aluminium — self
1.15 Rubber — self
1.20 Platinum — self
1.40 Silver — self
1.46 Indium — self
The setae on small animals feet conform to follow the surface so a high proportion of the area can have an attractive adhesion. By conforming to the surface there is never a high pressure exerted on a high point that would push the foot away from the surface and counter the adhesion.ItDoesn'tMatter said:For example, I know synthetic setae are very resistant to slipping on surfaces.
Yes, it is peculiar since the dry surfaces do not immediately cold weld to each other. Maybe there is enough surface oxidation to prevent a weld forming.Andy SV said:That's interesting I did not know that about self stick of metals
You may wish to review SAE paper #942484 (Chuck Hallum) for some very interesting findings on how a Top Fuel drag tire works. Statically, the coefficient of friction is 3.0 but dynamically the 36.0x17.0-16 Top Fuel tire generates close to 5.0 . We have some of the data you have requested and hope you find it helpful. The coefficient of friction is speed dependent and declines with speed. In our Pro Stock tire (33.0X17.0-15 in D-6 tread compound) the coefficient of friction was measured in the laboratory (flat belt treated with VHT track prep tackier application) for various speeds:
0 MPH 3.0
40 MPH 2.9
80 MPH 2.0
120 MPH 1.8
This is pure speculation but maybe the similarities of field allow the two samples to get closer together ... The only way I can think to say it is, less zero distance?Baluncore said:Yes, it is peculiar since the dry surfaces do not immediately cold weld to each other. Maybe there is enough surface oxidation to prevent a weld forming.
The crystal structure in the two samples is extremely unlikely to be aligned on the sample interface so the contact surface must be the average of all the diagonal contact “dislocations”, hence the high coefficient without a weld forming.
The thing that at first glance surprised me was indium. It has the highest static coefficient against itself in the list, yet it is used as the surface layer on thin shell engine bearings. I believe that is because it is highly resistant to acids and runs only against cast iron, steel or chrome that is very well lubricated with oil.
The list also demonstrates another reason why copper sheet makes such a good head gasket for old tractors with cast iron blocks and heads.
"Over wood"... What kind of wood and how was the surface prepared? Was it polished or roughed up? Was the aluminum polished or roughed up? The highest friction is when the two surfaces are like Velcro, even at the micro level. So, can we ask "what is the friction coefficient of sand paper on sand paper?" Why not?phinds said:Low grit sandpaper is really good at not slipping over wood
CWatters said:Interestingly metal on metal can be quite high..
http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
Car tire on Asphalt = 0.72
Aluminum on Aluminum 1.05 - 1.35
A coefficient of friction is a measurement of the force required to move one surface over another. It is a dimensionless value that represents the ratio of the force of friction to the normal force between the two surfaces.
The coefficient of friction is typically measured using a device called a tribometer. This device applies a known force to a test object and measures the force required to move it over a surface. The ratio of these two forces is the coefficient of friction.
The materials with the highest coefficients of friction are typically rough and coarse surfaces, such as sandpaper, rubber, and asphalt. These materials have a high level of surface roughness, which increases the amount of friction between them and another surface.
Knowing the coefficient of friction is important for understanding the behavior of objects in motion. It can help engineers design structures and machines with the appropriate amount of friction to ensure safety and efficiency. It is also important for predicting the performance of vehicles, such as tires on roads.
Yes, the coefficient of friction can be changed by altering the properties of the surfaces in contact. For example, adding a lubricant can reduce the coefficient of friction between two surfaces. Additionally, changing the surface roughness or texture can also affect the coefficient of friction.