energy,power,work Flashcards
Energy is
If something contains a store of energy it is
If something does not store energy then it
the capacity of something to do work:
able to do work.
will not work.
The law of conservation of energy states that…
we say taht energy is
What this means is that the
Energy cannot be created or destroyed, it can only change from one form to another.
conserved
the total amount of energy in a closed system remains constant, although how much of each form there is may change.
total energy …=total energy out of
into system
out of system
the uit of all forms of energy is
joules
list all forms of energy
kinetic, potential, gravitational potential, nuclear , internal, chemical, elastic,
A falling object (in a vacuum):
describe change in energy forms
Gravitational potential energy → Kinetic energy
describe change in energy forms
A gas cooker:
Chemical → Internal (Heat)
describe change in energy forms
An LED (Light Emitting Diode):
Electrical → Light
describe change in energy forms in page 53
Conservation of Energy in Multiple Stage….
for example
A fossil fuel power station takes chemical energy (the fuel) and uses it to produce electrical energy, but the individual steps are:…
Many processes involve several steps before energy ends up in its final form.
Chemical → Internal (heat) → Kinetic (steam) →
Kinetic (turbine and generator) → Electrical
In addition to the six forms of energy mentioned above, there are four ways in which energy can be transferred from one form to another:
list them
forces or mechanical working
eletrical currents or electrical working
heating
waves
In addition to the six forms of energy mentioned above, there are four ways in which energy can be transferred from one form to another:
describe Energy Dissipation
When energy is transferred from one form to another, not all of the energy will end up in the desired form (or place).
This lost energy often ends up being dissipated (spreading out into the environment), usually in the form of heat, light or sound.
The gravitational potential energy (GPE) of an object is the…
If an object is lifted up it will…GPE.
If it falls, it will …GPE.
energy it has due to its height in a gravitational field:
gain
lose
when an object is lifted
the work done against gravity is transformed into gravitational potential energy
gravitational potential energy is abbrevieted in
g.p.e.
the change in g.p.e. can be expreesed in the formula
The gravitational field strength (g) on the Earth is approximately
10 N/kg.
The kinetic energy (k.e) of an object is the
energy it has as a result of its speed.
when speed and velocity increase ….
k.e. increases
kinetic energy is related to the mass (m) and speed (v) of the object by the equation:
do problem page 56
calculate speed using k.e. formula
root 2k.e./m
the size of the velocity is equal to the …of the object
speed
when a car travels at constant speed, its kinetic energy is …as its …
the car still needs fuel(…)
to keep moving at a constant speed because it is doing
constant
speed not changing
chemical energy
work against frictional forces
do problem page 55
Energy resources are
large banks of energy that can be transferred into a form that can be used by society,
list the main energy resources and their energy form
describe the main energy resources and their energy form
A renewable energy resource is one that
is replenished at a faster rate than the rate at which it is being used.
A reliable energy resource is one that can
roduce energy at any time.
Non-reliable resources can only produce energy some of the time (e.g. when it’s windy).
Most of our energy resources on the Earth come from the
Sun
Most of our energy resources on the Earth come from the Sun:
The Sun heats up the atmosphere, creating wind and producing waves.
Water evaporated by the Sun falls as rain, filling up reservoirs.
Plants grown using sunlight form the basis for fuels – both biofuels and fossil fuels.
The Sun’s energy is produced by through the process of
The Sun’s energy is produced by through the process of nuclear fusion in its core.
Nuclear fusion involves
the collision (and bonding) of hydrogen nuclei to form helium nuclei, releasing nuclear energy in the process.
Some forms of energy, however, do not come from the Sun.
These include:
Geothermal – this comes from heat produced in the Earth’s core.
Nuclear – this comes from elements which make up a small proportion of the Earth’s crust.
Tidal – this comes (mainly) from the gravitational attraction of the moon.
Whenever energy is transferred from one form to another, some of that energy is
usually wasted and is transferred away from the system usually in the form of heat or waves (light and sound).
An efficient system is one where
most of the energy going into that system ends up in the form that is wanted.
An inefficient system is one where
most of the energy ends up in forms that weren’t wanted.
E.g. An old incandescent light bulb is inefficient because only a small amount of the electrical energy (5%) ends up as light.
The efficiency of a system is
the percentage of energy transferred from the original store that ends up in the intended form.
Efficiency can be calculated using the following equation:
Efficiency can also be written in terms of power (the energy per second):
Work is done whenever
The greater the force, the… the work
The larger the distance moved, the…. the work.
a force acts on an object that moves (or is moving) in the direction of the force.
greater
larger
Whenever any work is done,
The amount of energy transferred (in joules)
Whenever any work is done, energy
is equal to the work done (also in joules).
energy transferred (J) = work done (J)
Usually, if a force acts in the direction that an object is moving then the object will
gain energy.
If the force acts in the opposite direction to the movement then the object
lose energy.
The amount of work that is done if related to the size of the force, and the distance moved by the object, in the direction of the force:
The units of work are … but can also be given as
joules (J)
(Nm).
The power of a machine is
the rate at which the machine transfers energy.
The greater the rate at which energy is transferred,the ….
greater the power.
power is equal to …
because
equal to the rate at which work is done.
Because work done is equal to energy transferred,
Power is the
amount of energy transferred (or work done) every second.
Power, work and time are related by the following equation:
The unit of power is the..
which is the same as
watt (W
a joule per second (J/s).
Think of power as
“energy per second”.
Thinking of it this way will help you to remember the relationship between power and energy.
And to help you remember the unit of power: “Watt is the unit of power?”
describe solar energy
it makes use of energy from the sun
solar cells, wnown as photovoltaic cells convert light energy into electricity
wind energy
uses wind to turn turbines
wind energy turns the turbine blades in a wind turbine
the kinetic energy of the wind is conveted into electrical energy by the generator
wave energy
makes use of ocean waves to turn turbines
generatior are driven by the trasverse motion of waves.
the kinetic energy of the wave motion causes water to rise and fall in the air chamber
the air above the water causes the turbine to turn and electricity is produced by the generator
tidal energy
makes use of incoming and outgoing tides
tidal energy causes the water to move
it turns the turbine and electricity is generated
g.p.e. and k.e. convert into elecrical energy
geothermal energy
uses heat from the earth’score
water is fed down through pipes several kilometres
underground, passing through hot rocks
these rocks heat the water until it turns into very hot steam.
the steam is fed back up to the ground level and is used to turn turbines and generate electricity
hydroelectric energy
uses a dam to trap water
a dam is built to trap water, sometimes in a valley where there is an existing lake. Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive the generators that produce electricity
