Work, energy and power
Work and energy are mutually connected and must be considered together as work is often defined in terms of energy and vice versa.
Work can be generally defined as transfer of energy.
In physics we say that work is done on an object when you transfer energy to that object.
If one object transfers (gives) energy to a second object, then the first object does work on the second object.
Energy can be defined as the capacity for doing work.
The simplest case of mechanical work is when an object is standing still and we force it to move. Consider a small car with a broken engine in the center of the street. The driver can apply force, push it and move to the side of the street. The driver transfers energy to the car.
While the car is in motion (very slow one, but motion) it has energy.
The energy of a moving object is called kinetic energy.
For an object of mass m, moving with velocity of magnitude v, this energy can be calculated from the formula
(1)
EK is called a kinetic energy as it is the energy of moving object.
Let’s calculate the work done by a force acting on an object. First we will consider the simplest case when force is aimed in the same direction as the displacement. The amount of work done by the force in such a situation is equal to the product of force and displacement caused by this force.
W = F D (2)
W – work , F force, D – displacement. Unit of work is Newton times meter and is called Joule
1 Joule = 1 N x 1m
Energy has the same units. It is a consequence of the definition of work. Work done on an object can be transferred into the energy of this object, so units for these quantities must be the same.
The last word from the title of this paragraph –
power is the work done in a unit of time
In other words it is the rate of doing work.
The unit of power is
Watt = 1 Joule/ 1 second
In next few paragraphs we will explain in detail the three quantities briefly defined here.