In the pictures shown what do you thing the people are doing?

The people are doing some kind of work.Reading, writing, calculating, drawing are

examples of mental work. While running, swimming, playing are examples

of physical work.

In physics we recognise only physical or non mechanical work and that too only if there is some displacement. (the body has moved from one place to another place.)

Work done always consumes energy.When an applied force can set an object in motion or the

direction of the object is changed, then work is said to be done.

Sometimes when force is applied on a heavy object, but the object does not move, no work is said to be done.

From the pictures shown it is clear that work is said to be done only when the following two conditions are satisfied.

• A force must be applied on the object.

• The object should move from its resting position or there should be a change in shape or size of the object.

A person A moves an object through a distance of 100 metresAnd person B moves the same object through 50 metres. Who

has done more work?

A person moves a trolley weighing 100 kg for 10 metres and another person moves a trolley of 50 kg for 10 metres. Who has done more work?

The amount of work depends upon the force applied and the displacement (shortest possible distance in the direction of force) of the object.

Work is defined as the product of force and displacement.

WORK = FORCE x DISPLACEMENT= F X S

Unit of Work = 1 Newton x 1 metre = 1 Nm = 1 Joule1 kJ = 1000 J

Without energy our body gets tired. In order to do work we need energy.Energy needed by us is stored in food and which gets converted to energy when we

work.

Thus Everything in this universe is either matter or energy.

Matter is any physical substance which exists in nature in one form or other. (S,L,G)

Energy is the ability to do work.

More work needs more energy. Thus there is a direct relationship between work and energy.

The unit of energy is also Joule. Energy and work are measured in the same units, some of which include joules, ergs, electron-volts, calories, and foot-pounds.

Forms of Energy (few of them are)

• MECHANICAL ENERGY– KINETIC ENERGY– POTENTIAL ENERGY• Gravitational Potential Energy• Elastic Potential Energy

• OTHER FORMS OF ENERGY• Energy in action

o Sound, light, electrical, heat

• Stored energyo Chemical, magnetic, nuclear

What is mechanical energy?

The energy possessed by a body due to its state of rest or uniform motion is called mechanical energy.

The energy that a moving body produces is called movement or kinetic energy.

Greek word kinesis means motion.

The amount of kinetic energy depends on the mass and velocity of the moving object.

Definition – the energy possessed by a body due to its motion is called kinetic energy.

A tiny bullet can penetrate into thick sheets of metal, a storm can uproot big trees. HOW?

All due to their speed which increases the kinetic energy of a bullet or air by a very large amount.