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Home Newtonian Physics Vectors and Motion Examples Pushing a block up a ramp | |||||||
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Pushing a block up a ramp
Figure (g) shows a block being pushed up a frictionless ramp at constant speed by an applied force FA. How much force is required, in terms of the block's mass, m, and the angle of the ramp, θ?
Figure (h) shows the other two forces acting on the block: a normal force, FN, created by the ramp, and the weight force, FW, created by the earth's gravity. Because the block is being pushed up at constant speed, it has zero acceleration, and the total force on it must be zero. From figure (i), we find
|FA| = |FW| sin θ Since the sine is always less than one, the applied force is always less than mg, i.e., pushing the block up the ramp is easier than lifting it straight up. This is presumably the principle on which the pyramids were constructed: the ancient Egyptians would have had a hard time applying the forces of enough slaves to equal the full weight of the huge blocks of stone. Essentially the same analysis applies to several other simple machines, such as the wedge and the screw.
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Home Newtonian Physics Vectors and Motion Examples Pushing a block up a ramp |