In everyday life, we use terms like work and energy. The definition of work in physics means work is the force to move an object to some distance. In scientific ways, work is done only when you exert a force to move an object from one place to another.
Applying force and doing work has a difference. So, when you are using force, it means pushing or pulling, which tends to produce motion, tends or stops the motion. But doing work means when a certain required amount of force is applied on an object and the object tends to move in the required direction of the applied force, then you say work is said to be done.
The action of a force is associated with the action of energy. If the displacement is either perpendicular or zero to the force, then the work done by a force is zero. The work done can be positive or negative if the force and displacement are in the same or the opposite direction.
Definition of Work done
We say work is done when a force produces the motion. Work done involves both the application of the force on the body and the body’s displacement.
Consider a block of an object placed on a horizontal frictionless floor. A constant force (F) is acted upon as a block. Now, the action of this force is to move the body in a straight line in the direction of force through a distance (d). Now, you can say work (W) done by this force is equal to the product of the magnitude of the force applied and the distance through which the object moves. Work done formula is:
W=F*d
Where F=|F|
In this case, the force exerted on the body is constant, but the direction of displacement and direction of force influenced by this force is different. Hence, the force (F) reacts at an angle to the displacement (d):
W=|F| cos Ɵ * |d|
Thus, the work done is defined as the product of the magnitude of displacement d and the force component in the direction of displacement. Work has only magnitude and no direction. Hence, it is a scalar quantity. From the work formula, we can summarise that no work is done if:
- The force is zero
- The displacement is zero
- The force and displacement are mutually perpendicular to each other.
The most important condition for a force to do work is that an object produces the motion, i.e., the work done on an object is zero when the distance moved is zero.
For example, if a person stands still with heavy luggage in his hand, they do not work in this situation, but they may get tired soon since their luggage does not move at all. So, it can be concluded that work doesn’t need to be done whenever a force is applied to a body. But the work is done when force can move the body.
Work done formula
When a thrust is applied to a block with force (F), the body travels with a rising or a falling speed liable to the direction of the force; as the speed surges or declines, the kinetic energy of the system changes. Hence, the work done by a force is equal to the change in kinetic energy.
W=½ (mV2)-½ (mU2)=½ m(V2-U2)
Where V2-U2=2as
W=½(2mas)
Form Newton’s Second law of force, F=ma
W=F*s
The unit of work done in any unit of the system is equal to the unit of force multiplied by the unit of distance. The unit of work in the SI system is 1Nm which is called Joule (J).
1J=1Nm
Work done examples
Work done by a force on an object can be positive, negative and zero.
- Positive work done: The work done can be said positive if the force is in the same direction as the displacement. Examples are the motion of the ball dropping towards the ground where the displacement of the ball is in the direction of the force of gravity, kicking a football, riding a bicycle, moving and pushing a table, throwing a stone.
- Negative work done: The work done can be said negative if the force is in the opposite direction to the displacement. Examples are when a ball is thrown upwards, the displacement will be in the upwards direction, but the force because of the gravity on earth will be in the opposite direction. For a liquid flowing, viscous force acts opposite to the direction of the force and negative work is done. When you pull water from a well, work done is negative since the rope is pulled downwards, but the bucket is displaced upwards, stopping a moving object, work done by brakes in a vehicle.
- Zero work done: The work done is zero if the force is at a right angle to the displacement. Examples are when we push hard against a wall, the force applied does not work, since the displacement of the wall d=0, when you hold an object and walk when you stand with a big suitcase in your hands and do not move it.
Conclusion
We can conclude that the work is said to be done whenever a force is applied to move a body. Also, the work done by a force depends on two factors: the magnitude of the force and the distance by which the body moves in the direction of the force. Many physical situations can be simplified by understanding the work and better understanding the object over time.
Important FAQs
- Which are the factors that affect the work done?
The factors affecting the work done are force acting on an object, displacement of the object and the angle between the force and displacement.
- What are the types of work done?
The varieties of work done are positive work, negative work and zero work.
