Monday, September 23, 2013

Static vs. Kinetic Friction



I was watching Top Gear this weekend (obviously the UK version) and thought about static versus kinetic friction in terms of a drag race and why static friction coefficients are greater than kinetic friction coefficients.  The hosts often test to see how fast a car can go in a given distance.  When they first step down on the gas peddle, there is a significant amount of static friction preventing the car from moving immediately.  Enough force must be applied to get the car to move to overcome the molecular interactions of the tires and ground "locking" together.  Once the car is moving, these forces are easier to overcome because the car already moving and has acceleration, forces being applied, etc.  This means there is less kinetic friction to overcome because the molecular interactions aren't as "locked" together.  So once the car is moving, it speeds up really quickly.  So the coefficient of kinetic friction is less than the coefficient of static friction.

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