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I have a physics question that I don't understand conceptually:

The coefficient of kinetic friction between a skier's skis and the snow is 0.18 when the skier is sliding down one side of the valley. As the skier moves up the other side of the valley, the coefficient of kinetic friction exceeds 0.18 because gravity is acting against the skier's motion. True or False?

The answer is apparently false, but that doesn't make sense because the skier is slowing down, and therefore the coefficient of kinetic friction has to be increasing to go against its movement. Any help would be appreciated.

Qmechanic
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ORBITAL_PHOTON
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  • This skier is using the wrong wax. He should be around 0.04 to be competitive: https://ac.els-cdn.com/S1877705815015155/1-s2.0-S1877705815015155-main.pdf?_tid=69c6f979-5bc2-4d88-b1be-0ad2b792a8b7&acdnat=1523415388_1c2c9433d31a4f3446f6c39910eb46af – JEB Apr 11 '18 at 02:55
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    Related? https://physics.stackexchange.com/q/48534/ – Farcher Apr 11 '18 at 05:10

1 Answers1

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The coefficient of friction depends on roughness among others things. Does the roughness change just because you slow down?

No, you slow down because of that roughness. (I guess we are assuming stamped snow that doesn't deform while skiing. Otherwise we might argue that the roughness does indeed change.)

In general, unless the surface itself changes along the way, the coefficient of friction is always constant.

  • When skiing downhill, the weight pulls down and the kinetic friction up (it counteracts the motion direction) since the weight is largest, the skier speeds up downwards.
  • When skiing uphill, the weight still pulls downwards and kinetic friction does as well now (it still counteracts the motion). With both of these forces pulling downwards the skier is slowing down and eventually starts skiing backwards downwards.
Steeven
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