Lever

In a lever the relative positions of Force(F), Effort(e) and Load(L) may vary and this leads to different types of lever. The lever operates on the principle of moment.

First Order Lever

In first order lever, the fulcrum is between the load and the effort e.g crowbar, claw hammer,  pliers, scissors, see-saw e.t.c

Taking moment about F gives;

Clockwise moment = anticlockwise moment

Y×L=X×ELE=XY=M.A=V.R

Second Order Lever

In second order lever, the load is between the effort and the fulcrum. E.g wheelbarrow, bottle opener, nut cracker

Third Order Lever

In third order lever,  the effort is between the load and fulcrum. E.g Forearm of a human being, tongs etc.

LEVERS AND PULLEYS SLIDESHOW. Click to view next.

 Pulleys

Definition of Pulley

A simple pulley is a fixed wheel with a rope passing round a groove in its rim. A load is attached to one end of the rope while effort is applied at the other end. If there is no friction, load is equal to the effort which is equal to the tension in the rope.

L = T = E, therefore  M.A = V.R

For a block and tackle or systems of pulley of n pulleys, the velocity ratio is equal to the number of pulley.

Velocity ratio = number of pulleys = n

A system of pulley is used for lifting loads. They are used by builders for hauling heavy loads to high floors or in loading and unloading ships.

CALCULATIONS:

Example 1:

The velocity ratio and efficiency of a system of pulleys are 6 and 80% respectively. How much effort is required to lift a load of mass 120kg  with this system? [g = 10ms^-1]

Solution:

V.R = 6,  Efficiency = 80%,  Load = 1200N, e = ?

Calculating M.A,

Efficiency =M.AV.R×10080=M.A6×100M.A=80×6100=4.8M.A=LoadEffortEffort=LoadM.A=12004.8=250N

EVALUATION

A pulley system with a velocity ratio of 6 is used to raise a load of 80N through a vertical height of 16m,

1. Draw a diagram of this arrangement
2. Calculate the effort required in the system, if its efficiency is 70%.
3. Calculate the work done.