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.
- They help in lifting objects from the lower level to higher level.
- They help in lifting heavy loads during building.3. They help in off loading heavy vehicles.
- They help in towing vehicles.
- They are used to raise flags on the poles.
- Help to move window curtains.
TYPES OF PULLEYS.
- Single fixed pulley
- Single movable pulley.
- 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 = 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.
BLOCK AND TACKLE SYSTEM.
- It does work more easily because it is a combination of both fixed and movable pulleys.
- It changes direction of force.
- It reduces effort needed.
- The ratio of load to Effort is determined by the number of pulleys.
If A has 30teeth and B has 15teeth, howmany rotations does B make in one revolution?30divided by 15=2 turns.