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We already know that work is said to be done when a force produces motion.
The unit of work is Newton meter (N m) or joule (J). Thus 1 J is the amount of work done on an object when a force of 1 N displaces it by 1m along the line of action of the force.
The work done by a force can be either positive or negative or zero.
Positive Work
If a force displaces the object in its direction, then the work done is positive
So, W=Fd
An example of this kind of work done is the motion of the ball falling towards the ground where displacement of the ball is in the direction of the force of gravity.
Negative work
If the force and the displacement are in opposite directions, then the work is said to be negative.
For example, if a ball is thrown in an upwards direction, its displacement would be in an upwards direction but the force due to earth’s gravity is in the downward direction. So here in this case gravity is doing negative work when you throw the ball upwards. Hence the work done by the gravitational force is negative. Mathematically when displacement is opposite to the force work done is given by
Negative work just means that the force and the displacement act in opposite directions.
Case of zero work done
If the directions of force and the displacement are perpendicular to each other, the work done by the force on the object is zero.
For example, when we push hard against a wall, the force we are exerting on the wall does not work, because in this case, the displacement of the wall is d = 0. However, in this process, our muscles are using our internal energy and as a result, we get tired.
physicscatalyst.com/Class9/work_and_energy.php
courses.lumenlearning.com/physics/chapter/7-1-work-the-scientific-definition/
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