# Is there any material that has a higher kinetic friction than static friction?

Is there a material that has higher kinetic friction than static friction?

You can assume it's sliding on any surface you want.

Better if you come up with one that has this property on a standard flooring material: steel, wood, smooth concrete, tile, asphalt, etc.

Also better if the material has this property at a macro scale.

• Does shear thickening material count?
– hazzey
Commented May 4, 2016 at 1:20
• You might consider specifying if you are interested in viscous friction (fluids) or Coulomb (sliding) friction. Commented May 4, 2016 at 13:29
• I don't think it exists, but it could be that a material rapidly heats up upon moving, increasing the friction by that. Mostly friction reduces under temperature, but some materials don't, like hazzey mentioned.
– Bart
Commented May 7, 2018 at 15:27

Friction is not a property of a material, it is a property of the interface between two objects, which may be the same or different materials. One interface I can think of that has that property is a thin layer of grease -- the force required to move increases with velocity.

• But that force is not "caused" by kinetic friction, so it does not really answer the question. Commented May 5, 2016 at 21:49

Sliding friction must, logically always be less than static friction. This becomes obvious when you look at it in terms of forces rather than coefficients.

Consider a block resting on a flat surface. You apply a small force to one side of the block to try to slide it along. Initially it doesn't move as the reaction force provided by friction increases in line with the force you exert.

Say that applying 10N of force is just enough to overcome static friction and get the block moving. Now if the sliding friction becomes greater the 10N force is no longer enough to overcome it and so it stops and your back to a static condition.

Another way to look at this is that friction is a reaction force so it can never be greater than the force applied otherwise you would be effectively getting work from nowhere.

However it is certainly possible to have materials whose friction properties change as a result of friction, for example carbon-carbon brakes are most effective at quite high temperatures.

There is also viscous drag which is proportional some function of speed although it is not really very meaningful to talk about static friction in this context.

The numbers for static and kinetic friction in aluminum-on-aluminum interactions, cited by @albseb back in 2016, are unreliable. Strangely though, they're the only published values.

I'm a physics student finishing my bachelor degree this year, and I'm doing my senior thesis with two other students on this exact topic - we may even try to publish it depending how much we can accomplish.

We've only just begun the project, but as far as we've found the values μs=1.05-1.35 and μk=1.4 seem to be the result of a ~30 year-long game of telephone. Without going into too much detail, we've found that a static friction value of 1.05 is somewhat reliable; we found it in the records of a 1940 MIT conference. However, the kinetic value is unfounded as far as we can tell. Following the rabbit hole of citations for the kinetic value of 1.4 led to a paper that did not support this number - a dead end.

What's interesting is how little published data there actually is on aluminum-aluminum friction. We're aiming to fix that in the coming months!

Apparently Aluminium - Aluminium (clean and dry) has a higher coefficient for kinetic friction than static friction.

The numbers I've found listed are:

• Static: 1.05-1.35
• Kinetic: 1.4

I dont think so. as kinetic force is always lesser than static. Here is a similar discussion

Similar question

The link is about the theory behind the static and kinetic friction. the coefficient of static friction can never be less than the coefficient of kinetic friction. Having greater kinetic than static friction just doesn't make any sense.

• This reads as a comment and not a full answer. Linking to an external site, even a StackExchange site, without an explanation or summary of the linked site is a poor answer. Explain why another reader may want to click through. Summarize the findings from the other question.
– user16
Commented May 4, 2016 at 12:06
• My bad. I dont think so. as kinetic force is always lesser than static. Here is a similar discussion [Similar question][1] [1]: physics.stackexchange.com/questions/541/… So, the link is about the theory behind the static and kinetic friction. the coefficient of static friction can never be less than the coefficient of kinetic friction. Having greater kinetic than static friction just doesn't make any sense. Commented May 4, 2016 at 13:34