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ropo
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Relationship Between Static And Kinetic Coefficient Of Friction

07/13/2016 2:42 AM

Is there any existing formula or model for converting static coefficient of friction to kinetic coefficient of friction.
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Tornado
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#1

Re: Relationship between static and kinetic coefficient of friction

07/13/2016 2:49 AM

My bet would be no, or at best with a large ± factor.

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Randall
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#2

Re: Relationship between static and kinetic coefficient of friction

07/13/2016 5:32 AM

No: definitely not.

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Rixter
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#3

Re: Relationship Between Static And Kinetic Coefficient Of Friction

07/13/2016 7:44 AM

Depends on the materials involved.

Approximate coefficients of friction

MaterialsStatic Friction, {\displaystyle \mu _{\mathrm {s} }\,}Kinetic/Sliding Friction, {\displaystyle \mu _{\mathrm {k} }\,}
Dry and cleanLubricatedDry and cleanLubricated
AluminiumSteel0.610.47

[13]

Alumina ceramicSilicon Nitride ceramic0.004 (wet)

[14]

BAM (Ceramic alloy AlMgB

14)

Titanium boride (TiB

2)

0.04–0.05

[15]

0.02

[16][17]

BrassSteel0.35-0.51

[13]

0.19

[13]

0.44

[13]

Cast ironCopper1.050.29

[13]

Cast ironZinc0.85

[13]

0.21

[13]

ConcreteRubber1.00.30 (wet)0.6-0.85

[13]

0.45-0.75 (wet)

[13]

ConcreteWood0.62

[18]

CopperGlass0.68
CopperSteel0.530.36

[13]

GlassGlass0.9-1.0

[13]

0.4

[13]

Human synovial fluidCartilage0.01

[19]

0.003

[19]

IceIce0.02-0.09

[20]

Polyethene

Steel0.2

[13][20]

0.2

[13][20]

PTFE (Teflon)

PTFE (Teflon)0.04

[13][20]

0.04

[13][20]

0.04

[13]

SteelIce0.03

[20]

SteelPTFE (Teflon)0.04

[13]-0.2[20]

0.04

[13]

0.04

[13]

SteelSteel0.74

[13]-0.80[20]

0.16

[20]

0.42-0.62

[13]

WoodMetal0.2–0.6

[13][18]

0.2 (wet)

[13][18]

WoodWood0.25–0.5

[13][18]

0.2 (wet)

[13][18]

https://en.wikipedia.org/wiki/Friction
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WJMFIRE
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#7
In reply to #3

Re: Relationship Between Static And Kinetic Coefficient Of Friction

07/13/2016 3:00 PM

Another clear example of why we use rubber tires on concrete roads instead of cartilage tires on Human Synovial Fluid roads.

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phoenix911
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#4

Re: Relationship Between Static And Kinetic Coefficient Of Friction

07/13/2016 7:54 AM

Rixter has a good chart. which reminds me, look under conveyor belt design such as Intralox, if I recall, they had some info.

For materials listed as well as not listed its empirical data.... in other words, you'll have run tests.

Physics 101, the proceedures and formula to be solve for the coefficient of friction would be listed.

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JohnDG
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#5

Re: Relationship Between Static And Kinetic Coefficient Of Friction

07/13/2016 8:15 AM

Here's a scatter chart of kinetic vs static (dry & clean) coefficients from Rixter's chart, for the entries for which both were given. I took the arith. men where a range was given. Not much sign of a relationship there.

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Rixter
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#6

Re: Relationship Between Static And Kinetic Coefficient Of Friction

07/13/2016 2:57 PM

You can measure the static and kinetic friction using a ramp which can be elevated on one end until the object under test begins to slide (static friction) or continues to slide at a constant rate (kinetic friction). The friction coefficient is the tangent of the angle.

http://physics.bu.edu/~duffy/semester1/c6_measuremus.html

One interesting fact is that the coefficient of kinetic friction is independent of the area in contact. This can be demonstrated by making a wooden block from a section of 2x4. The angle at which it slides uniformly down a ramp is the same whether it is resting on the large side or small side. The reason is that the frictional force (parallel to the ramp) is proportional to area x pressure. Since pressure is (normal force)/area, 'area' cancels out.

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JohnDG
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#8
In reply to #6

Re: Relationship Between Static And Kinetic Coefficient Of Friction

07/13/2016 7:57 PM

I learnt a big lesson doing that experiment as a schoolkid (about 15yo). It seemed so obvious to me that I slewed the recorded results to show that the friction was proportional to the contact area. After I was pulled up, I repeated the experiment - this time writing down exactly what the spring balance read (was a bit of a dodgy way of measuring it anyway) and got a better result. First (and last) time I've bent experimental results (I hope!).

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ropo
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#9
In reply to #8

Re: Relationship Between Static And Kinetic Coefficient Of Friction

08/06/2016 2:37 PM

Thanks, am contemplating a simulation on it.
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