### 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