Mechanics in Exercise

Part I | Part II


Wheels and Axles

Pulleys

Simple pulley: No force/distance trade off, only directional change. Cables may travel through multiple stationary pulleys and will still offer no force/distance trade off. Compound pulley: Load (R) moves half distance cable is pulled so the effort (F) is halved. Opposite end of cable is stationary so compound pulley rotates and travels upward with load. Split pulley: When both cables are pulled simultaneously, load is distributed equally between each side (lower pulley does not rotate and load is moved full height). When only one cable is pulled while the opposite cable is anchored, the split pulley acts as a compound pulley.

Cams

Requires half the effort to raise load as compared to simple pulley. In this position, load also moves through half the distance as compared to side with motive force. Requires at least the same motive force as resistive force to lift load. Both sides of cam move through same distance. Requires twice the effort to raise load as compared to simple pulley. In the position, load moves through two times the distance as compared to side with motive force.

Incline Plane

Pushing a load up a 30 degree ramp is twice the distance as raising the load vertically but requires half the effort (plus the effort to overcome friction). Pushing a load up a 45 degree ramp requires approximately 71% the effort as raising the load vertically.

Gears, belts, and chains


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