Transcript Energy - handsonict.com

DTTP Science
Energy
Energy
What is energy?
What do we already know?
Brainstorm session
Energy
Several distinct forms of energy.
The language we use in everyday talk gets in
the way of a deeper understanding of energy.
Energy
Energy is not used up,
it is just converted.
Energy
As an abstract idea,
energy is difficult to understand.
Implications for the National Curriculum.
In primary schools, teachers focus on the
effects of energy and rarely study energy
itself.
Energy
Trainees are expected to understand some of
the fundamental ideas about energy and see
how they apply to the ideas taught in
schools.
Energy
What is energy?
Without energy nothing happens
Energy
Energy is the capacity to do work.
Work is done when objects are moved
or heated.
Energy
Energy can be converted from one form to
another such as when coal or oil is burnt in a
power station.
The heat produced by this process is used to
make steam which turns a generator.
This mechanical energy is converted into
electrical energy.
Energy
Fuels and food are sources of energy.
This energy can be traced back to the plants,
including the myriad of single-celled plants,
which used solar power to create their
structures including leaves, stems, roots and
fruits.
Energy
• Fuel in the form of petrol gives cars the
capacity to do work.
• A car engine does work on the wheels to
make the car move.
• Electrical energy from a battery does work
on the filament of a bulb to make it glow.
• The gravitational pull of the Earth does work
on a cyclist as they roll down a hill.
Energy
• A stretched catapult elastic does work on the
stone to make it move.
• A moving hammer does work on a nail to
push it into a piece of wood.
Energy is measured in Joules (J).
The same unit is used to measure work.
Energy
Force
A force is a push or a pull.
To exert a force you must have energy.
Forces can:
 stretch or squash objects
 change the speed of an object
 alter the direction of an object’s movement
Energy
Force
Examples of force are push, pull and their
combinations – twist and bend
Gravity is either a push or a pull – most likely
a pull.
Centrifugal is a nice word
The unit in which forces are measured is
newtons (N). What is Newton’s 3rd Law?
Energy
Work
Work is done when an object moves,
electricity flows or an object is heated.
In moving objects, one joule is defined as
the work done when a force of 1N moves a
distance of 1 metre.
1 joule = 1 newton x 1 metre
Energy – the Go in the world
All energy comes from the sun as radiated heat.
Plants convert this to potential or stored energy.
Animals eat or otherwise use the plants and store it
to do work. All movement using the potential energy
is Kinetic energy - action
Work
In electrical energy, one joule of work is done when
one watt of power acts for one second.
Watts x seconds = work done (joules)
Energy
Forms of energy
Kinetic energy is the energy of motion.
All moving objects have kinetic energy. The heavier
and faster the moving object the more energy it has.
Chemical energy is the energy
associated with food and fuels.
Chemical changes produce new substances.
Chemical changes can sometimes be reversed.
Energy
Gravitational potential energy is the
energy of a position of an object.
We can calculate the potential energy of an object if
we know its mass and the distance it is raised. The
greater the height and the mass the more potential
energy an object has.
Heat energy is the energy of hot objects.
A spark from a sparkler has a high temperature but
relatively little heat energy compared with a large
hand-hot radiator.
Energy
All these are only tags for confusion
Electrical potential energy is the
ability of an electric current to do work.
A cell makes electrical energy from a
chemical reaction.
Energy
Sound energy is a form of kinetic energy.
Sound makes objects and materials vibrate.
Light energy is a form of electromagnetic
radiation.
Light energy from the sun can be converted directly
into electricity in a solar cell.
Nuclear energy is released when a
neutron hits the nucleus of a uranium 235
atom.
The atom splits into 2 parts and smaller particles,
releasing a huge amount of energy as it does so.
This process is called nuclear fission.
Energy
Energy and fuel
Food and fuel contain potential that is
released when these are combined with
oxygen.
Energy
Fuels for generating electricity
There are three main classes of fuels which
can be used to generate electricity:
 fossil fuels such as gas, oil and coal
 renewable fuels such as wood
 nuclear fuel such as uranium
What other ways are there to generate
electricity?
Energy
• Tidal power – the motion of tides coming in and
out of estuaries can be used to drive turbines.
•
Push and pull
• Hydroelectric power – the potential energy of
water is used to turn generators. The higher the
drop the more energy can be generated.
•
Push
• Wind power – moving air can be used to turn
propellers.
•
Push
Energy
• Wave power – moving air creates friction across
the surface of water and makes waves which
can be used to turn generators.
• Geothermal power - the interior of the Earth is
very hot. Where this heat is very close to the
surface, e.g. in Iceland, it can be used to heat
water which in turn is used to drive generators.
• Solar power – can directly produce electricity
using photoelectric cells
Energy
Chemical changes produce
electricity
Luigi Galvani
Allessandro Volta
Some cells are made using carbon and zinc as
the two terminals separated by a chemical
paste. Electricity flows from the zinc to the
carbon.
Energy
Energy transfers in biological processes
At the base of the vast majority of food chains are green
plants which use the energy of the sun to drive the
chemical reactions of photosynthesis.
It is the green plants’ ability to make starch and sugar
from carbon dioxide and water which distinguishes them
from all other living things.
Energy flows within an ecosystem are complex.
Energy
Energy flows in ecosystems
The energy from the sun is used by plants to
photosynthesise.
Some of the plant food is used directly by birds,
herbivorous animals and small arthropods such as
insects and mites. These small animals are in turn
preyed upon by carnivores.
Some creatures are omnivores, consuming both plants
and animals.
Energy
Converting energy in our bodies
Digestion
Respiration
Energy
A person’s body requires different amounts
of fuel to perform functions:
kJ used per hour (approx.)
 sleeping
 sitting
 standing
 walking
 running
 very hard exercise
270
420
440
850
1500
2500
Energy
Heat energy
Heat energy is transferred by three processes:
 conduction
 convection
 radiation
Energy
Energy Changes
Energy cannot be created or destroyed. Energy
can only change in form.
A bungee jumper jumping off a bridge involves:
 gravitational potential energy on the bridge
 increasing kinetic energy as they fall
 increasing elastic strain potential energy in the elastic
 increasing kinetic energy as they spring upwards
 energy dissipated as they hang motionless before being
helped down
Energy
Where does energy appear in the
Science NC and the QCA Unit Plans?
What are the links with other NC
subjects?
Energy
A summary of key points
Energy
• energy is the capacity to do work
• work is done when an object moves,
electricity flows or an object is heated
• energy can be in a number of different
forms
• energy can be converted from one form to
another
• energy cannot be created or destroyed
Energy
• food and fuel do not contain energy but energy
is released when the food or fuel is combined
with oxygen
• energy is released from nuclear material when
nuclei are split
• chemical changes produce electricity
• food pyramids summarise energy transfers in
biological systems
• heat energy moves from hotter objects to colder
Energy
Some questions to consider
Energy
Question 1
Imagine we were able to collect all the
gases given off by a burnt candle.
Would the mass of the gases be:
less than the original candle?
more than the original candle?
the same as the original candle?
Energy
Answer to Question 1
More than the mass of the original ……
……… because burning the wax is a
constructive process in which oxygen
is combined with the elements which
make up the wax.
Energy
Question 2
When plants photosynthesise, what
chemical bonds are they breaking in
the materials they use?
Energy
Answer to Question 2
They are pulling apart the oxygen and
carbon from the carbon dioxide……….
…….and they are separating the
oxygen from the hydrogen in the water
molecules.