We are studying friction. To move an object requires a force. This force is equal to the friction coefficient (Greek letter mu) times the Normal Force (mass times gravity expressed in Newtons). To demonstrate the friction coefficient of different materials we placed an object on a wooden ramp and raised the ramp until the object started to slide. We then recorded the angle of the board. We repeated the same exercise with different materials taped to the board including: aluminum foil, parchment paper, light or fine grade sandpaper (high grit number) and rough or heavy grade sandpaper (low grit number). Interesting fact: the grading of sandpaper is based on the number of holes per square inch in the screen used when sieving the grains of of grit during sandpaper manufacture. Thus fewer holes are bigger holes which allow larger grains to pass through.
Results: aluminum foil is smoother than wood, parchment paper smoother than foil. Large grit is rougher than small grit sandpaper and both had a higher coefficient of friction than the wood.
To calculate the static coefficient of friction, find the formula in module 7.
The coefficient of static friction is the tangent of the angle. This is not true for the coefficient of kinetic friction! Why is the mass or weight (mass times gravity) not used in this calculation?
The mass determines how much force is pushing the object down the slope. The mass also determines how much the object is pushing down on the board. The additional force pushing the object down the slope is offset by the additional static friction.
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