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Work is done when the force applied to an object moves that object. The amount of work done depends upon two factors:

  • Size of the force on the object
  • The distance the object moves

Work is calculated by multiplying the force by the amount of movement of the object. The equation can be stated as:

Work done  = Force * Distance

The unit of force is newtons and the unit of distance is meters. Work is measured in joules.

Work formula example
If a force of 20 newtons is applied to an object and the object moves 2 meters as a result of this force then the work done can be calculated as
Work = force * distance
    = 20 N * 2 m
    = 40 Nm = 40 Joules

Work and energy
Work is closely related to energy. When work is done energy is transferred from one place to another.

Work done (Joules) = Energy transferred (Joules)

The unit of energy is the same as the unit of work that is Joules. Therefore to do 100 Joules of work, you must transfer 100 Joules of energy. Energy is defined as the capacity to do work.

Potential energy is the energy stored within an object by virtue of its position, electric forces or other factors. The most common form of potential energy is the gravitational potential energy that is possessed by an object due to its vertical position and the mass of the object.

Kinetic energy is the energy produced when an object is in motion. Kinetic energy depends on the mass and the velocity of the object. Kinetic energy is a scalar as it does not have a direction.

Work energy principle
The work energy principle states that the work done by all forces acting on an object is equal to the change in the kinetic energy of that object. If the net work done by all forces is positive then the kinetic energy of the object increases. If the net work done by all forces is negative then the kinetic energy of the object decreases.

The work energy principle can be derived from Newton’s second law of motion that states that, “The rate of change of momentum of a body, is directly proportional to the force applied. This  change in momentum occurs in the direction of the applied force.”

Did you know: Work is also done when gases expand and contract as even in this case energy is being transferred.

Work and Power
Power is the measure of the rate at which work is being done. Sometimes work can be performed quickly while at other times it might be performed slowly. Thus power can be computed by the equation:

Power = Work / time

The unit of work is Joules and the unit of time is seconds. The unit of power is watts. A Kilowatt is equal to 1000 Watts.

Did you know: 1 horsepower is equal to 750 watts

Power can be used to determine the rate at which a machine is capable of doing work. Power can also be computed as

Power     = work / time
Since work is equal to force * distance
Power    = force * distance / time
    = force * velocity

Example:
Question: Calculate the power of a machine that perform 6000 Joules of work in 1 minute?
Answer:
Work done = 6000 J
Time take = 1 minute = 60 seconds
Power     = work/ time
    = 6000/ 60
    = 100 Watts

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