## Thursday, May 17, 2007

### X revision - Machines

What is machine?A machine is a device by which we can either overcome a large resistive force at some point by applying a small force at a convenient point and in a desired direction or by which we can obtain a gain in speed.

The energy lost in overcoming the force of friction between the moving parts of a machine is the most common type of loss of energy in it.

In actual practice, the mechanical advantage of for all practical machines is always less than velocity ratio as velocity ratio as efficiency is less than 1.

what is a lever?
A lever is a rigid, straight or bent bar which is capable of turning about a fixed axis.

The mechanical advantage of lever is equal to the ratio of the length of its effort arm to he length of its load arm.

For class I levers, the mechanical advantage and velocity ration can be have any value greater than 1, equal to 1 or less than 1.

The mechanical advantage of and velocity ration of class II levers are always more than 1.

The mechanical advantage of and velocity ration of calls III levers are always less than 1.

What is an inclined plane?

An inclined plane is sloping surface that behaves like a simple machine whose mechanical advantage is always greater than 1.

What is fixed pulley?
A pulley which has is axis of rotation fixed is called a fixed pulley.

A pulley whose axis of rotation is not fixed in position or space is called a movable pulley.

In a block and tackle system, the effort gets multiplied n times, where n is the total number of pulleys in the system.

In block and tackle system, the pulleys in the lower block should be as light as possible and the friction in pulleys should be minimized by the use of lubricants.