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

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.

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.

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.

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.

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.

› 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)

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

Example & exercise p.85

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

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