Download Station 2: Kinetic Energy

Station 1: Mechanical Energy
The concept of energy was first introduced in the chapter States of Matter, where it is defined
as the ability to cause change in matter. Energy can also be defined as the ability to do work.
Work is done whenever a force is used to move matter. When work is done, energy is
transferred from one object to another. For example, when the batter in Figure below uses
energy to swing the bat, she transfers energy to the bat. The moving bat, in turn, transfers
energy to the ball. Like work, energy is measured in the joule (J), or newton·meter (N·m).
It takes energy to swing a bat. Where does the batter get her energy?
Energy exists in different forms, which you can read about in the lesson “Forms of Energy”
later in the chapter. Some forms of energy are mechanical, electrical, and chemical energy.
Most forms of energy can also be classified as kinetic or potential energy. Kinetic and potential
forms of mechanical energy are the focus of this lesson.
Mechanical energy is the energy of an
object that is moving or has the potential
to move. It is the sum of an object’s
kinetic and potential energy.
In Figure below, the basketball has
mechanical energy because it is moving.
The arrow in the same figure has
mechanical energy because it has the
potential to move due to the elasticity of
the bow. What are some other examples
of mechanical energy?
Kinetic and potential energy add up to mechanical energy.
Station 2: Kinetic Energy
Moving things have kinetic energy. The heavier a thing is and the faster it moves the more
kinetic energy it has. All moving things have kinetic energy, even very large things, like planets,
and very small ones, like atoms.
What do all the photos in Figure below have in common? All of them show things that are
moving. Kinetic energy is the energy of moving matter. Anything that is moving has kinetic
energy—from the atoms in matter to the planets in solar systems. Things with kinetic energy
can do work. For example, the hammer in the photo is doing the work of pounding the nail
into the board. You can see a cartoon introduction to kinetic energy and its relation to work at
this URL:http://www.youtube.com/watch?v=zhX01toLjZs.
All of these photos show
things that have kinetic
energy because they are
moving.
The amount of kinetic
energy in a moving object
depends on its mass and
velocity. An object with
greater mass or greater
velocity has more kinetic
energy.
The kinetic energy of a moving object can be calculated with the equation:
This equation for kinetic energy shows that velocity affects kinetic energy more than mass
does. For example, if mass doubles, kinetic energy also doubles. But if velocity doubles, kinetic
energy increases by a factor of four. That’s because velocity is squared in the equation. You
can see for yourself how mass and velocity affect kinetic energy by working through the
problems below.
Problem Solving
Problem: Juan has a mass of 50 kg. If he is running at a velocity of 2 m/s, how much kinetic
energy does he have?
Solution: Use the formula:
You Try It!
Problem: What is Juan’s kinetic energy if he runs at a velocity of 4 m/s?
Problem: Juan’s dad has a mass of 100 kg. How much kinetic energy does he have if he runs at
a velocity of 2 m/s?
Station 3: Potential Energy
Did you ever see a scene like the one in Figure below? In many parts of the world, trees lose
their leaves in autumn. The leaves turn color and then fall from the trees to the ground. As the
leaves are falling, they have kinetic energy. While they are still attached to the trees they also
have energy, but it’s not because of motion. Instead, they have stored energy, called potential
energy. An object has potential energy because of its position or shape. For example leaves on
trees have potential energy because they could fall due to the pull of gravity.
Before leaves fall from trees in autumn, they have potential energy. Why do they have the
potential to fall?
Gravitational Potential Energy
Potential energy due to the position of an object above Earth is called gravitational potential
energy. Like the leaves on trees, anything that is raised up above Earth’s surface has the
potential to fall because of gravity. You can see examples of people with gravitational
potential energy in Figure below. At the URL below, you can watch a cartoon introduction to
gravitational potential energy.
Elastic Potential Energy
Potential energy due to an object’s shape is called elastic potential energy. This energy results
when elastic objects are stretched or compressed. Their elasticity gives them the potential to
return to their original shape. For example, the rubber band in Figure below has been
stretched, but it will spring back to its original shape when released. Springs like the
handspring in the figure have elastic potential energy when they are compressed. What will
happen when the handspring is released?
A)
C)
B)
D)
E)
Station 4: Sound energy
A vibrating drum and a plucked guitar string transfer energy to the air as sound. Kinetic energy
from the moving air molecules transfers the sound energy to your eardrum.
The drummer in Figure below is hitting the drumheads with drumsticks. This causes the
drumheads to vibrate. The vibrations pass to surrounding air particles and then from one air
particle to another in a wave of energy called sound energy. We hear sound when the sound
waves reach our ears. Sound energy can travel through air, water, and other substances, but
not through empty space. That’s because the energy needs particles of matter to pass it on.
Vibrating objects such as drumheads produce sound energy.
If an object is vibrating quickly, it has a higher frequency and shorter wavelength. As a result,
the sound is more high-pitched. On the other hand (or claw), if it is vibrating more slowly, the
wave has a lower frequency and longer wavelength, emitting a more low-pitched sound. This
quality is measured in units of Hertz, with more Hertz indicating higher pitches.
If the sound wave is larger in height, it has greater amplitude and therefore a louder sound. If
the sound wave is smaller in height, it has lower amplitude and a quieter sound.
Station 5: Thermal energy
Thermal energy is what we call energy that comes from heat. A
cup of hot tea has thermal energy in the form of kinetic energy
from its particles. Some of this energy is transferred to the
particles in cold milk, which you pour in to make the tea cooler.
The atoms that make up matter are in constant motion, so they
have kinetic energy. All that motion gives matter thermal
energy. Thermal energy is defined as the total kinetic energy of
all the atoms that make up an object. It depends on how fast
the atoms are moving and how many atoms the object has. Therefore, an object with more
mass has greater thermal energy than an object with less mass, even if their individual atoms
are moving at the same speed. You can see an example of this inFigure below.
Atoms are moving at the
same speed in the pasta on
the fork as they are in the
pasta on the plate.
However, there are more
atoms of pasta on the
plate, so it has more
thermal energy.
Heat and temperature are not the same thing, although both are concerned with thermal
energy.
 The heat an object contains is the amount of its thermal energy, measured in joules or J.
 The temperature of an object is to do with how hot or cold it is, measured in degrees
Celsius. Note that the unit of temperature is written as °C, (not °c or oC). A thermometer
is used to measure the temperature of an object
Let's look at two examples to see the difference between heat and temperature.
Example 1
A swimming pool at 30°C is at a lower temperature than a cup of tea at 80°C. But the
swimming pool contains more water, so it stores more thermal energy than the cup of tea.
Example 2
To boil water we must increase its temperature to 100°C. It takes longer to boil a large beaker
of water than a small beaker because the large beaker contains more water and needs more
thermal energy to reach 100°C.
Thermal energy can be transferred in three different ways: conduction, convection, and
radiation.
Station 6: Conduction (Thermal Energy Transfer)
Thermal energy can be transferred by the process of CONDUCTION.
When a substance is heated, its particles gain energy and vibrate more vigorously. The
particles bump into nearby particles and make them vibrate more. This passes the thermal
energy through the substance by conduction, from the hot end to the cold end.
Stages in conduction
This is how the handle of a metal spoon soon gets hot when the spoon is put into a hot drink.

Substances that allow thermal energy to move easily through them are called conductors.
Metals are good conductors of thermal energy.

Substances that do not allow thermal energy to move through them easily are
called insulators. Air and plastics are insulators.
Station 7: Convection (Thermal Energy Transfer)
Thermal energy can be transferred by CONVECTION. The particles in liquids and gases can
move from place to place. Convection happens when particles with a lot of thermal energy in
a liquid or gas move, and take the place of particles with less thermal energy. Thermal energy
is transferred from hot places to cold places by convection.
Station 8: Radiation (Thermal Energy Transfer)
All objects transfer thermal energy by infrared radiation. The hotter an object is, the more
infrared radiation it gives off.
No particles are involved in radiation, unlike conduction and convection. This means that
thermal energy transfer by radiation can even work in space, but conduction and convection
cannot.

Radiation is how we can feel the heat of the Sun, even though it is millions of kilometres away
in space.

Infrared cameras give images even in the dark, because they are detecting heat, not visible
light.
Conduction and convection need moving particles to transfer the thermal energy, but
radiation does not.
Station 9: Chemical energy
Chemical energy is stored in wood and released when the wood burns.
Some chemical reactions release energy. For example, when an explosive goes off, chemical
energy stored in it is transferred to the surroundings as thermal energy, sound energy and
kinetic energy.
Energy is stored in the bonds between atoms that make up compounds. This energy is
called chemical energy, and it is a form of potential energy. If the bonds between atoms are
broken, the energy is released and can do work. The wood in the fireplace in Figure below has
chemical energy. The energy is released as thermal energy when the wood burns. People and
many other living things meet their energy needs with chemical energy stored in food. When
food molecules are broken down, the energy is released and may be used to do work.
Station 10: Electrical energy
Electrons are negatively charged particles in atoms. Moving electrons have a form of kinetic
energy called electrical energy. If you’ve ever experienced an electric outage, then you know
how hard it is to get by without electrical energy. Most of the electrical energy we use is
produced by power plants and arrives in our homes through wires. Two other sources of
electrical energy are pictured in Figure below.
A lightning bolt is a powerful discharge of electrical
energy. A battery contains stored chemical energy and
converts it to electrical energy.
Bulb and battery
A battery transfers stored chemical
energy as electrical energy in moving charges in wires. For
example, electrical energy is transferred to the surroundings
by the lamp as light energy and thermal energy.
Station 11: Nuclear Energy
The nuclei of atoms are held together by powerful forces. This gives them a tremendous
amount of stored energy, called nuclear energy. The energy can be released and used to do
work. This happens in nuclear power plants when nuclei fission, or split apart. It also happens
in the sun and other stars when nuclei fuse, or join together. Some of the sun’s energy travels
to Earth, where it warms the planet and provides the energy for photosynthesis
(see Figure below).
In the sun, hydrogen nuclei fuse to form helium nuclei. This releases a huge amount of energy,
some of which reaches Earth.
Station 12: Energy transfer diagrams
Energy transfer diagrams
show the locations
of energy
stores and energy
transfers.
For example, consider the
energy transfers in the
simple electrical circuit to
the left.
We can show the transfers like this:
The battery is a store of chemical energy. The energy is transferred by electricity to the lamp,
which transfers the energy to the surroundings by light. These are the useful energy transfers
- we use electric lamps to light up our rooms.
But there are also energy transfers that are not useful to us. In the example above, the lamp
also transfers energy to the surroundings by heating. If we include this energy transfer, the
diagram looks like this:
Station 13: Sankey diagrams
Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the
line or arrow, the greater the amount of energy involved. This Sankey diagram for the lamp
shows that it transfers most of the energy by heating, rather than by light:
Notice that the total amount of energy transferred to the surroundings is the same as the
amount of electrical energy. We say that the energy has been conserved. Energy is always
conserved, it is never "lost" or "wasted", although some energy transfers are useful and some
are not.
Station 14: Electromagnetic Energy
Energy that the sun and other stars release into space is called electromagnetic energy. This
form of energy travels through space as electrical and magnetic waves. Electromagnetic
energy is commonly called light. It includes visible light, as well as radio waves, microwaves,
and X rays (Figure below).
Radio waves, microwaves, and X rays are examples of electromagnetic energy.
Station 15: Non-renewable Sources of Energy: FOSSIL FUELS
We get energy from many different types of energy resources, including fuels, food and stores
of energy such as batteries or the wind. We can divide energy resources into two
categories: non-renewable and renewable.

Non-renewable energy resources cannot be replaced once they are all used up.

Renewable energy resources can be replaced, and will not run out.
On the this page we'll look at non-renewable resources.
Fossil fuels
Coal, oil and natural gas are called fossil fuels. They formed
millions of years ago from the remains of living things. Coal was
formed from plants. Oil and natural gas were formed from sea
creatures.
The energy stored in the fossil fuels originally came from sunlight.
Plants used light energy from the Sun for photosynthesis to
make their chemicals. This stored chemical energy was
transferred to stored chemical energy in animals that ate the
plants. When the living things died, they were gradually buried by
layers of rock. The buried remains were put under pressure and
chemical reactions heated them up. They gradually changed into the fossil fuels.
When the remains of the plants and animals became fossil fuels, their chemical energy was
stored in the fuels. The energy is transferred to the surroundings as thermal energy
and light energy when the fuels burn.
Once we have used them all up, they will take millions of years to replace, if they can be
replaced at all. For this reason we call fossil fuels non-renewable energy resources.
Most of the UK's electricity is generated in power stations using fossil fuels. Thermal energy
released from the burning fuel is used to boil water to make steam, which expands and turns
turbines. These drive the generators to produce electricity.
1. the fuel is burned to boil water to make steam
2. the steam makes a turbine spin
3. the spinning turbine turns a generator which produces electricity
4. the electricity goes to the transformers to produce the correct voltage
As the fossil fuels are non-renewable energy resources, and they also produce pollution when
they burn, we are aiming to produce more of our electricity using other, renewable energy
resources. This will reduce the rate at which the fossil fuels are used up.
Reducing energy use
We can also reduce the rate at which the fossil fuels are used up by saving energy. For
example, we can:

walk to instead of getting using cars where possible

turn down the heating

turn off the lights when leaving the room
Station 16: Renewable Resources
Renewable energy resources can be replaced, and will not run out. Be careful - it is not true to
say that they can be re-used.
1) BIOMASS
Biomass fuels come from living things. Wood is a biomass fuel. As long as we continue to plant
new trees to replace those cut down, we will always have wood to burn. Just as with the fossil
fuels, the energy stored in biomass fuels came originally from the Sun.
2) WIND
Wind is caused by huge convection currents in the Earth's atmosphere,
driven by heat energy from the Sun. The moving air has huge amounts
of kinetic energy, and this can be transferred into electrical energy
using wind turbines. Wind turbines cannot work if there is no wind, or
if the wind speed is so high it would damage them.
3) WATER
Moving water has kinetic energy. This can be transferred into useful energy in different ways.
For example:

wave machines use the up and down movement of waves to turn electricity generators

tidal barrages are built across the mouths of rivers. As water moves in or out of the river
mouth when the tide turns, the kinetic energy in the water is used to turn electricity
generators.

Hydroelectric power (HEP) schemes store water high up in dams. The water has gravitational
potential energy which is released when it falls. As the water rushes down through pipes, this
stored energy is transferred to kinetic energy, which turns electricity generators.
An energy transfer
diagram for an HEP
scheme:
4) GEOTHERMAL
In some places the rocks underground are hot. Deep wells can be drilled and cold water
pumped down. The water runs through fractures in the rocks and is heated up. It returns to
the surface as hot water and steam, where its energy can be used to drive turbines and
electricity generators
5) SOLAR POWER
Solar cells are devices that convert light energy directly into electrical energy. You may have
seen small solar cells on calculators. Larger arrays of solar cells are used to power road signs,
and even larger arrays are used to power satellites in orbit around Earth.
Solar panels are different to solar cells. Solar panels do not generate electricity. Instead they
heat up water directly. A pump pushes cold water from a storage tank through pipes in the
solar panel. The water is heated by heat energy from the Sun and returns to the tank. They are
often located on the roofs of buildings where they can receive the most sunlight.
Generating electricity
Electricity can be generated in many ways, including:

in power stations using fossil fuels or biomass fuel

using wind turbines

using hydroelectric power schemes

using wave power or tidal power

using solar cells.