PULLEYS

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PULLEYS

Apulley is a wheel with grooved rim that rotates freely about an axle through a centre.A rope or chain passes over the pulley and is prevented from slipping by the grooved

The frame which holds the pulley is called block.

IMPORTANCE OF PULLEYS.

  1. They help in lifting objects from the lower level to higher level.
  2. They help in lifting heavy loads during building.3. They help in off loading heavy vehicles.
  3. They help in towing vehicles.
  4. They are used to raise flags on the poles.
  5. Help to move window curtains.

TYPES OF PULLEYS.

  1. Single fixed pulley
  2. Single movable pulley.
  3. Block and Tackle system.

SINGLE FIXED PULLEY.

The effort applied is equal to the load.It changes the direction of forceBoy applying the down ward force, work becomes easier.The M.A of a single fixed pulley is one (1).

Example;If a load of 30kgf is to be raised using a single fixed pulley, find the effort needed

M.A =1L=30kgf

E=??

M.A = load/Effort

1 = 30/EE x 1 = 30

E = 30kgf.

SINGLE MOVABLE PULLEY

It is supported on two ropes.The rope is pulled up wards.The pulley moves with the load.Each of the ropes share a half of the effort needed.The rope moves twice as far as the load.The M.A advantage of single movable pulley is 2 (two)Effort applied is half the load force. (It reduces the effort needed)

Example. If a load of 30kgf is to be raised using a single movable pulley, Find the effort needed.

work
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BLOCK AND TACKLE SYSTEM.

  1. It does work more easily because it is a combination of both fixed and movable pulleys.
  2. It changes direction of force.
  3. It reduces effort needed.
  4. The ratio of load to Effort is determined by the number of pulleys.
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If A has 30teeth and B has 15teeth, howmany rotations does B make in one revolution?30divided by 15=2 turns.