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### KS4 Physics

Contents Contents

Types of Energy

Contents

Types of Energy

Different types of energy

Nuclear energy

Gravitational potential energy

Kinetic energy

Summary activities

Rita’s bedroom

Rita is not very energetic in the morning.

What types of energy can you see in her bedroom?

Different types of energy

Energy cannot be seen or observed directly and can be thought of as the ability to do work.

Energy exists as different types and can be transferred, or changed, from one form to another.

The amount of energy an object has is measured in joules (J).

There are nine different types of energy that you need to be aware of:

light

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sound

kinetic

nuclear

electrical

chemical

elastic

gravitational

thermal

Light energy

Light is a form of electromagnetic radiation. This is energy carried

by vibrating electric and magnetic forces in transverse waves.

Light travels in straight lines

and has the properties of waves.

The Sun is a light source, as is

a filament lamp or a firefly.

How do we see objects?

by reflected light

Which colour of light has the most energy: red or violet?

violet

Sound energy

Sound energy needs a medium through which to travel.

Sound energy is transmitted by vibrations of the particles in the medium through which it is travelling .

Sound travels in longitudinal waves.

The louder the sound, the more energy it transmits.

The quieter the sound, the

less energy it transmits.

Thermal energy

All objects have thermal energy. It is the energy a substance has due to the kinetic energy (movement) of its particles.

The more thermal energy a material has, the hotter it is.

In which state of matter (solid, liquid or gas), do water molecules have the most thermal energy and why?

Thermal energy

Ice (frozen water) has the least thermal energy.

Its molecules have little kinetic energy and so are unable to move past each other.

Liquid water has more thermal energy.

Its molecules have more kinetic energy. They can move past each other but are still held together.

Water vapour has the most thermal energy.

Its molecules have lots of kinetic energy and are moving so fast they are no longer held together.

Electrical energy

Electrical energy is carried by wires and is the energy that electrons have as they flow around a circuit.

Electricity is useful because it is a convenient way of transporting energy to a particular location or device.

Electrical energy can be used to do work in a wide range of different devices.

Elastic energy

If a material like this sponge is squashed (compressed), when the material is released it has the potential to return to its original shape.

The energy stored in a compressed material is

called elastic energy.

The same is true for materials that are stretched and have the potential to return to their original shape. They also store elastic energy.

Chemical energy

Chemical energy is a type

of stored energy that is released by chemical reactions.

Fuels, food and batteries all contain chemical energy.

When a fuel burns, energy is released by a chemical reaction with oxygen.

Respiration is the process used by the body to release the chemical energy stored in digested food.

Contents

Types of Energy

Different types of energy

Nuclear energy

Gravitational potential energy

Kinetic energy

Summary activities

Nuclear fission

The particles in the nucleus of an atom are held together by strong forces.

Some atoms, such as uranium, have a very large unstable nucleus, which can split into two smaller nuclei.

This splitting is called fission and releases huge amounts of nuclear energy.

The release of nuclear energy is exploited in nuclear power stations and some atomic bombs.

Nuclear fission

A uranium nucleus is split by bombarding it with neutrons. This fission forms two new elements and two neutrons.

The new neutrons can cause other nuclei to split, which releases even more neutrons. This is achain reaction.

Nuclear fusion

Atomic nuclei can join together, which also releases huge amounts of energy. This joining together is known as fusion.

Nuclear fusion is the process that releases energy inside stars such as the Sun.

Contents

Types of Energy

Different types of energy

Nuclear energy

Gravitational potential energy

Kinetic energy

Summary activities

Gravitational potential energy

Any object in a gravitational field has gravitational potential energy due to its position in that field.

The Moon has gravitational potential energy due to the gravitational field of the Earth.

The Earth has gravitational potential energy due to the gravitational field of the Sun.

The gravitational potential energy depends on the distance between the two objects.

Gravitational potential energy

The gravitational potential energy of an object on Earth depends on its weight and its height above the Earth’s surface.

When a bungee jumper starts to fall they start to lose gravitational potential energy.

As the elastic cord pulls the bungee jumper back up, they gain gravitational potential energy.

Calculating gravitational potential energy

GPE = weight x height

The gravitational potential energy (GPE) of an object depends on its weight and its height.

The equation for calculating GPE is:

What are the units of GPE, weight and height?

- GPE is measured in joules (J).
- Weight is measured in newtons (N).
- Height is measured in metres (m).

Calculating gravitational potential energy

GPE = weight x height

gravitational field strength

GPE = mass x x height

The weight of an object is its mass multiplied by the strength of the gravitational field acting on the object.

This can be substituted into the GPE equation to give:

What are the units involved?

- GPE is measured in joules (J).
- Mass is measured in kilograms (kg).
- Gravitational field strength is measured in newtons per

kilogram (Nkg-1).

- Height is measured in metres (m).

Gravitational potential energy problem

A seagull with a weight of 30N flies at a height of 10m above the ground.

How much gravitational potential energy does the seagull have?

GPE of seagull = weight x height

=30 N x 10 m

=300 J

Calculating gravitational potential energy

GPE = weight x height

When an object falls or is raised, it is useful to calculate the change in gravitational potential energy (GPE).

To do this, the change in height is used in the GPE equation:

change in GPE = weight x change in height

What are the units involved?

- Change in GPE is measured in joules (J).
- Weight is measured in newtons (N).
- Change in height is measured in metres (m).

Gravitational potential energy problem

A parachutist of weight 600N jumps from a plane, which is 2000m above the ground.

How much gravitational potential energy will the parachutist have lost when she reaches the ground?

GPE = weight x height

change in GPE = weight x change in height

= 600 N x 2000 m

= 1200000J

Types of Energy

Different types of energy

Nuclear energy

Gravitational potential energy

Kinetic energy

Summary activities

Kinetic energy

So, if the velocity of a car is slightly above the speed limit, its kinetic energy is much greater than it would be at the speed limit. This means it is more difficult to stop the car

and there is more chance of an accident.

Kinetic energy is the energy an object has because it is moving.

- The greater the mass of a moving object,

the greater its kinetic energy.

- If the mass is doubled, the kinetic energy is doubled.

- The greater the velocity of a moving object,

the greater its kinetic energy.

- If the velocity is doubled, the kinetic energy is quadrupled!

Calculating kinetic energy

kinetic energy =½ x mass x velocity2

KE = ½mv2

The kinetic energy (KE) of an object depends on its mass and its velocity.

The equation for calculating kinetic energy is:

What are the units of kinetic energy, mass and velocity?

- Kinetic energy is measured in joules (J).
- Mass is measured in kilograms (kg).
- Velocity is measured in metres per second (ms-1).

Kinetic energy problem

A car has a mass of 1500kg and is travelling at a velocity of 10ms-1.

What is the kinetic energy of the car?

kinetic energy = ½xmass x velocity2

= ½ x 1500kg x (10ms-1)2

= 75000J

Rearranging the kinetic energy equation

KE = ½mv2

Ö

2KE

m

2KE

v2

velocity =

mass =

Sometimes it is necessary to rearrange the kinetic energy equation in order to calculate the mass or the velocity of a moving object.

What are the rearranged versions of this equation for calculating mass and velocity?

TIP: If you do not think you can rearrange the KE formula during an exam, learn the rearranged formulae instead.

Kinetic energy problem

Ö

2 x 3000000

100000

Ö

=

2KE

m

velocity =

Ö

=

60

A train has a mass of 100 000 kg.

If its kinetic energy is 3 MJ,

what velocity is it travelling at?

3 MJ = 3000000J

=7.75 ms-1

Types of Energy

Different types of energy

Nuclear energy

Gravitational potential energy

Kinetic energy

Summary activities

Glossary

- chemical energy – The energy stored in chemicals and which is released when they react.
- elastic energy –The energy stored in a material because it is being stretched or compressed.
- gravitational potential energy –The energy an object has because of its position in a gravitational field.
- kinetic energy –The energy an object has because it is moving.
- nuclear energy –The energy stored in an atom’s nucleus.
- nuclear fission – The splitting of a large nucleus into two nuclei, which releases very large amounts of energy.
- nuclear fusion –The joining together of two atomic nuclei, which releases very large amounts of energy.
- thermal energy –The energy of a substance due to the

movement of its particles.

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