1. Work
Crash course and synopsis

2. What is work?
Work (W) Work is defined as a force acting upon an object to cause a
displacement. It is expressed as the product of force and displacement
in the direction of force. W=F x s.
Work is done when a force produces motion.
In the following picture you can see that a man is pushing the box with a
certain force say 5N to cover a distance of 2m so his work done will be
10J. Joules is the SI unit of work = 1 KG m2/s2.
Energy is capacity of a body to do work.

3. F[N] F[N]
S[m]

4. Work depends upon-
The work done on a body depends upon two factors: Magnitude of the force (F),
and. The displacement through which the body moves (s).
We can now say that work done in moving body is equal to the product of the
force exerted on the body and the distance moved by the body in the direction of
force.
When the body is moved on the ground by applying force, then the work is done
against friction(which opposes motion of the body)

5. Unit of work
Work is the product of force and distance. Now unit of force is newton(N) and
distance is metre (m) so the unit of work is newton metre (Nm). When a force of 1
newton moves a body through a distance of 1m in its own direction, then work
done is known as 1 joule. So, 1 joule = 1 newton 1 metre
1J = 1 Nm
Thus the SI unit of work is joule(J). Work is a scalar quantity.

6. Work Done Against Gravity
Climbing stairs and lifting objects is work in both the scientific and everyday sense—it is work done against
the gravitational force. When there is work, there is a transformation of energy. The work done against the
gravitational force goes into an important form of stored energy that we will explore in this section.

7. Let us calculate the work done in lifting an object of mass m through a height h,
such as in Figure 1. If the object is lifted straight up at constant speed, then the
force needed to lift it is equal to its weight mg. The work done on the mass is then
W = Fd = mgh. We define this to be the gravitational potential energy (PEg
) put into
(or gained by) the object-Earth system. This energy is associated with the state of
separation between two objects that attract each other by the gravitational force.
For convenience, we refer to this as the PEg
gained by the object, recognizing that
this is energy stored in the gravitational field of Earth.

8. Why do we use the word “system”? Potential energy is a property of a system rather than
of a single object—due to its physical position. An object’s gravitational potential is due
to its position relative to the surroundings within the Earth-object system. The force
applied to the object is an external force, from outside the system. When it does positive
work it increases the gravitational potential energy of the system. Because gravitational
potential energy depends on relative position, we need a reference level at which to set
the potential energy equal to 0. We usually choose this point to be Earth’s surface, but
this point is arbitrary; what is important is the difference in gravitational potential energy,
because this difference is what relates to the work done. The difference in gravitational
potential energy of an object (in the Earth-object system) between two rungs of a ladder
will be the same for the first two rungs as for the last two rungs.

9. W=MGH
When the work is done against gravity.
This formula will be used to take out work done when a
body is being lifted

10. Question-
The work done by a force acting obliquely is given by the formula: W = F cos θ
ｘs.What will happen to the work done if angle θ between the direction of force and
motion of the body is increased gradually? Will, it increases, decrease or remain
constant?
Solution-
As we increase the force’s angle with respect to the direction of motion, less and
less work is done along the direction that we are considering; and more and more
work is being done in another, perpendicular, the direction of motion.