Work, Energy and Power Overview

Work done is the product of the component of the force in the direction of the displacement and the magnitude of the displacement.

Subjects > Physics > Work, Energy and Power

Before moving direct into the problems of Work and Energy, let's see what we need to know about Work and Energy.

Work done

When a force causes a body to move, work is being done on the object by the force. The amount of work done when a force acts on a body depends on two things:

  • the size of the force acting on the object
  • the distance through which the force causes the body to move in the direction of the force
Hence,
Work done = force x distance
`W = F times d`
Force (F) is measured in Newtons `N` and distance (d) in metres `m` hence,
`W = N times m =` Joules (`J`)
∴ The SI Unit of Work done is Joule

So now we can say, Work is the measure of energy transfer when a force (`F`) moves an object through a distance (`d`).
When work is done, energy has been transferred from one energy store to another, and so:

Energy transferred = Work done
Both Energy transferred and Work done are measured in Joules (`J`)

Energy

Energy simply means ability of doing work. A system possesses energy if it has ability to do work.

Energy can exist in many different forms. All forms of energy are either kinetic or potential.

Kinetic Energy (`K*E`)
is the energy possessed by the body or an object due to its motion. Examples of the forms of Kinetic energy are:

  • mechanical energy - motion of macroscopic systems (machines, wind energy, wave energy, sound energy).
  • thermal energy - motion of particles of matter (geothermal energy)
  • electrical energy - motion of charges (lightning, household current)
  • electromagnetic radiation - disturbance of electric and magnetic fields or the motion of photons (solar energy, radio, microwaves)

Formula:
Kinetic energy = `1/2 times mass times (velocity)^2 = 1/2 mv^2`
SI unit of Kinetic energy is `J o u l e (J)`

Potential Energy (`P*E`)
is the energy possessed by the body or an object due to its position. Examples of the forms of Potential energy are:

  • gravitational potential energy (roller coaster, waterwheel, hydroelectric power)
  • electromagnetic potential energy
  • strong nuclear potential energy
  • weak nuclear potential energy (radiactive decay)

Formula:
Potential Energy = `mass times gravity times height = mgh`
SI unit of Potential Energy is `J o u l e (J)`

Power

Power is the rate of doing work. That is to say, is the amount of energy transferred or converted per unit time.
`Power = (Wo rk)/(time) = (en ergy)/(time)`

  • Has no direction, hence it is scalar quantity
  • SI unit of power is Joule per second, known as `W a t t (W)`
  • Another traditional measure of power is `ho rsepower (hp)`
  • `1 hp = 746 W`

Now, let's move in. Solved Work and Energy problems.

Recommended Lessons

Before moving direct into the problems of Work and Energy, let's see what we need to know about Work and Energy.

Work done

When a force causes a body to move, work is being done on the object by the force. The amount of work done when a force acts on a body depends on two things:

  • the size of the force acting on the object
  • the distance through which the force causes the body to move in the direction of the force
Hence,
Work done = force x distance
`W = F times d`
Force (F) is measured in Newtons `N` and distance (d) in metres `m` hence,
`W = N times m =` Joules (`J`)
∴ The SI Unit of Work done is Joule

So now we can say, Work is the measure of energy transfer when a force (`F`) moves an object through a distance (`d`).
When work is done, energy has been transferred from one energy store to another, and so:

Energy transferred = Work done
Both Energy transferred and Work done are measured in Joules (`J`)

Energy

Energy simply means ability of doing work. A system possesses energy if it has ability to do work.

Energy can exist in many different forms. All forms of energy are either kinetic or potential.

Kinetic Energy (`K*E`)
is the energy possessed by the body or an object due to its motion. Examples of the forms of Kinetic energy are:

  • mechanical energy - motion of macroscopic systems (machines, wind energy, wave energy, sound energy).
  • thermal energy - motion of particles of matter (geothermal energy)
  • electrical energy - motion of charges (lightning, household current)
  • electromagnetic radiation - disturbance of electric and magnetic fields or the motion of photons (solar energy, radio, microwaves)

Formula:
Kinetic energy = `1/2 times mass times (velocity)^2 = 1/2 mv^2`
SI unit of Kinetic energy is `J o u l e (J)`

Potential Energy (`P*E`)
is the energy possessed by the body or an object due to its position. Examples of the forms of Potential energy are:

  • gravitational potential energy (roller coaster, waterwheel, hydroelectric power)
  • electromagnetic potential energy
  • strong nuclear potential energy
  • weak nuclear potential energy (radiactive decay)

Formula:
Potential Energy = `mass times gravity times height = mgh`
SI unit of Potential Energy is `J o u l e (J)`

Power

Power is the rate of doing work. That is to say, is the amount of energy transferred or converted per unit time.
`Power = (Wo rk)/(time) = (en ergy)/(time)`

  • Has no direction, hence it is scalar quantity
  • SI unit of power is Joule per second, known as `W a t t (W)`
  • Another traditional measure of power is `ho rsepower (hp)`
  • `1 hp = 746 W`

Now, let's move in. Solved Work and Energy problems.

Recommended Lessons