Work And Its Types | What is Work Done In Physics

Work And Its Types

You would agree that its hard work pulls a truck, to lift a stack of books, from the floor to the shelves or to pull a sofa set across the room. Indeed, all of these examples agree with the everyday meaning of work. Any activity that requires muscular or mental effort is work. In common parlance, you are working hard. All this hard work may involve very little work if we go by the scientific definition of work. In day-to-day life, we consider any useful physical or mental labour as work. Activities like playing in a field, talking with friends, humming a tune, watching a movie, attending a function are sometimes not considered to be work. What constitutes work depends on the way we define it. We use and define the term work differently in science.

SCIENTIFIC CONCEPT OF WORK

In physics, work has a much more precise definition. In all the examples cited above, there is something in common. In each case, you do work by exerting a force on the body while the body moves from one place to the other. Lift a book through a height. To do this you must apply a force. The book rises up. There is a force applied to the book and the book has moved. Hence, work is done. Thus, two conditions need to be satisfied with the work to be done: 1. A force should act on the object and 2. The object must get displaced.

If any of the above two conditions are not met, then scientifically we say that no work has been done. work is done when a force 'F' pushes a body through a displacement 's'

if an object undergoes a displacement ab = s, the work done by the force F is W =Fs. The work done by a constant force is defined as the product of the force in the direction of the displacement and the magnitude of the displacement.

Since F is in the direction of 's', hence work done by the force F is given by

W = Force*displacement = Fs

Work is a scalar quantity. It has only a magnitude

Types of Work

Work is of three depending on the angle between the force vector and the displacement vector. 1.Positive work 2.Negative work 3.Zero work

Positive work:

Work done is said to be positive if the applied force is in the direction of the displacement.

EXAMPLES:

• Work is done by gravity if a body falls towards the earth.
• Work is done by a horse pulling a cart.
• Work is done by the stretching force acting on a spring.

Negative work:

Work done is said to be negative if the applied force is in a direction opposite to that of displacement.

EXAMPLES:

• Work is done by the braking force when brakes are applied to a vehicle

• Work is done by friction.

• Work is done by the force of gravity when a body is projected away from the surface of the earth.

Zero Work:

Work done is said to be zero if the applied force is zero or displacement is zero or the angle between displacement and force is 90 degree.

 EXAMPLES:

• Work is done by the tension in the string of a simple pendulum.
• Work is done by centripetal force.
• Work is done by a coolie-carrying load on his head and walking straight on a level platform.

Zero work: Force is applied but displacement is zero

UNITS OF WORK

In the cgs system, the absolute unit of work is erg. Work done is said to be one erg if a force of one dyne displaces a body through a distance of one centimetre in its own direction. Mathematically, we have,

1 erg = 1 dyne* 1 cm In SI, the absolute unit of work is the joule (J). Work done is said to be one joule if a force of one newton displaces a body through a distance of one metre in its own direction Mathematically, we have 1 joule = 1 newton * 1m Further 1 joule = 1N* 1m = 10^5 dyne * 10^2cm =10power7 erg