In our daily life , the word "work" means any kind of mental and Physical activities , But in physics , the terms work has entirely a different meaning.
Scientific Conception of work :
Definition: Work is said to be done by a force on a body or an object of the force applied causes a displacement in the body or the object.
Factors on which work done depends :
(1). The magnitude of the applied force (F).
W ∝ F
(2). The distance travelled by the body on the application of force .
W ∝ S ( displacement)
Work done by a contant force :
(i) When a contant force is applied in the horizontal direction.
W = F.S
(ii) When force is applied at an angle with the horizontal direction.
W = FScosΘ
# Dot product of two Vector quantities gives a scalar quantity. So work is a scalar quantity.
Thus , Work done on a body by a force is defined as the product of the magnitude of the displacement and the force in the direction of the displacement of the body.
Type of work done :
1. Positive work done : if Θ is 0°
W = FScos0° = FS
Such work done is known as Positive work done.
# if Θ < 90° ( Acute angle ) , then work is positive .
# Work done by the force of gravity on a falling body is positive.
# When a coolie lifts a box from the ground to put it on his head.
2. No work done or Zero work done : if Θ = 90° the force F acts at right angles to the displacement ( S ) of the body , then
W = FScos90° = 0
# When a stone attached to a string is rotated in a horizontal circular path , the force acting on the stone is always towards the centre of the circular path. This force is called Centripetal force F.
# if S = 0 , the body does not move from it's position , then W = 0.
# When a person pushes a wall but fail to move the wall , then work done by the force on the wall is zero.
3. Negative work done : if Θ = 180° , force (F) acts just opposite to the displacement ( S ) of the body .
W = FScos180° = -FS
# When Θ is 90<Θ<180 , then work also negative.
# When an object is lifted upward to a certain height , then the work done by the force of gravity on the object is negative.
# In a tug of war , the work done by the losing team is negative.