Contents are appropriate for IGCSE Physics

2.  In everyday activities, the word ‘work’ is used.
 Work is defined as: the product of force and
distance in the direction of the force.
Work down = force x distance in the direction of the force
W = F x d
 Work is only done when distance moved is in
the direction of the force.
 A person carrying a bucket of water on the
head and covers a distance of 20km gets tired.
However, no work has been done. This is
because the applied force is not in the
direction of the force.
give example & exercise

3.  What is energy?
› The ability to do work
 List down different forms of energy.
› Kinetic, GPE, chemical, elastic, …
 What is the difference between Kinetic and
Potential energies?
› Kinetic = energy in a body in motion
› Potential = energy due to an object’s position
 Explain the following:
› Chemical, electrical, nuclear, thermal and
radiated energy
 State the law of conservation of energy
and give examples.

4.  The Sun supplies 98% of the Earth’s
energy.
 The Sun is 75% hydrogen.
 It releases energy by a process called
Nuclear fusion.
 In Nuclear fusion, two hydrogen atoms
come together to form Helium. In the
process, energy is released. This energy is
the one that reaches the Earth in form of
light and heat (Electromagnetic energy).
 It takes 8minutes for energy from the Sun
to reach the Earth.

5.  Another process that produces Nuclear
energy is Nuclear Fission.
 In nuclear fission, atoms of heavier
elements are split into smaller atoms and
in the process release energy. This
process takes place in nuclear power
plants.

6.  Albert Einstein calculate the energy
released in the Sun as:
E = mc2
 Where:
› E = energy
› m = mass
› c = speed of light (3.0 x 108m/s)
 The energy from the Sun is non-renewable.
It will one day run out.
 Non-renewable energy sources: are energy
sources that when once used, cannot be
used again. E.g.
› Fossil fuels: coal, oil and natural gas.
› Nuclear fuels: nuclear fusion and nuclear fission.

7.  Renewable energy sources: are energy
sources that can be used over and over
again without running out. E.g.
› Hydroelectric energy: a river fills a lake
behind a dam. Water flowing down from the
lake turns generators.
› Tidal energy: a lake fills when the tide comes
and empties when it goes back. This process
turns generators.
› Wind energy: turbines driven by wind.
(Windmills)
› Wave energy: generators are driven by up-
and-down motion of waves.

8. › Geothermal energy: water is pumped down
to hot rocks underground and rises as steam
and turns the generators.
› Solar energy: solar panels absorb solar
energy and convert it to electrical energy.
› Biofuels: plant and animal matter are used to
make biofuels. (Ecology process)

9.  A vehicle covers 10km faster than a
bicycle.
 A vehicle consumes energy faster than a
bicycle.
 The rate of doing work is called POWER.
Power = work done
time taken
 Or
Power = energy transformed
time taken

10. Example & exercise p.85

11.  An engine can only do work when
energy is supplied to it.
 In reality, no engine can use all the
energy supplied usefully. No engine is
100% efficient.
 The efficiency of a system is defined as:
the percentage ratio of useful energy
output to the total energy input.
 Mathematically:
efficiency (Є) = useful energy output x 100%
total energy input

12.  Efficiency can also be calculated using:
Є = useful work done x 100%
total energy input
Є = power dissipated x 100% = power used x 100%
power input total power input
Example:
The crane below lifts a 100kg block of
concrete through a vertical height of 21m is
16s. If the power input to the motor is
2500W, what is the efficiency of the motor?
p.85