Transcript energy - SchoolNotes

Energy
What is energy
Energy is the action or stored
ability to cause change in matter
through movement, temperature
or state of matter
It is also the ability to create
work
It is not a substance like matter,
but rather an unseen force that
is present in the universe
What does energy do
Energy moves things
Energy lights things
Energy heats things
Energy changes things into other
things
Energy can not be created or
destroyed, but it can change its
form
Where does energy come from
Energy can not be created or
destroyed, but it can change from
one form to another
This is know as the Law of
Conservation of Energy (Newton’s
First Law of Thermodynamics
Forms of Energy
Types (conditions) of energy
Kinetic energy – energy that is
actively doing something
Potential energy – stored energy
that is waiting to be used
There are seven forms of energy
Mechanical – energy of movement
Electrical – energy of electric
charges
Chemical – energy of chemical
compounds
Heat – energy in an object
Nuclear – energy inside an atom
Solar – energy of the sun
Sound – the energy of vibration
Mechanical Energy
Energy of motion and
position
If not moving, an object has
potential mechanical energy
– car parked on a hill
If moving, an object has
kinetic mechanical energy
– car rolling down a hill
Mechanical Energy
Electrical Energy
Energy of electrical charges
Electrical energy in a conductor
-current electricity
–House wiring
Electrical energy not in a
conductor- static electricity
–Doorknob spark
–Lightning
Electrical Energy
Chemical Energy
Energy of chemical bonds
Released when chemical
bonds are broken
–Explosions
–Burning wood
–Energy in candy bar
oxygen
Chemical energy
Bond (Energy
stored in bond)
hydrogen
Bond (Energy
stored in bond)
Bond (Energy
stored in bond)
Hydrogen
Water
produced
Energy
release
Heat (Thermal) Energy
Energy of moving atoms in an
object
More movement - more energy
More energy - more movement
Large objects have more energy
than small objects if temperature is
same
Temperature is average heat energy
Simulation of heating of
gases
Nuclear Energy
Energy stored in nucleus of
atoms
Holds atomic particulars
together
Tremendous release of
energy if atom is split
–Atomic bomb
–Nuclear power plants
Solar Energy
Energy from solar radiation
Largest source of energy on
earth
Many other energy sources
come from solar energy
–Wind power
–Fossil fuels
–Biomass fuel
Provides most of heat and
light on earth
Energy Transformation and
Transfer
Energy Transformations
Energy changes from form to form
Electricity is generated by
mechanical energy (generators) that
are turned by other forms of energy:
Heat - steam from:
sun (Solar)
burning fuels (Chemical)
fission reactions (Nuclear)
–Mechanical – moving water or wind
Electricity can be transformed easily
Electricity can be transformed into
many other forms of energy
–Light energy – light bulbs
–Sound energy – radios
–Chemical energy – battery charger
–Mechanical energy – electric motor
–Heat energy – toaster
Not all energy is transformed
Some is lost as heat or friction
Efficiency is a measure of how
much energy is transferred in
percent
Examples:
–Chemical to mechanical (engine,
your body) loses heat
–Electrical to mechanical (motor)
loses to friction
High efficiency = little energy lost
Energy can be stored
Energy can be stored for use
–Mechanical energy can be stored
as elastic or gravitational potentia
–Electrical energy can be stored as
chemical potential in a battery
–Plants store chemical energy
through photosynthesis
–Chemical energy is stored in
explosives
The Law of Conservation of
Energy
Energy is never lost even with low
efficiency
All energy is conserved in one form
or another
The Law of Conservation of Energy
states: “Energy is not created or
destroyed, it only changes forms
Energy can be transferred
Energy can be moved (transferred)
from one object to another
–Mechanical – legs using motion
move bicycle pedals which give
motion to the wheels
–Heat – moving atoms bump into
each other and transfer
movement from one to another
Three Forms of Heat Transfer
Conduction
–Solid objects in direct contact with
each transfer heat by conduction
transfer
Convection
–Gases and liquids transfer heat
away from the source by
convection transfer
Radiation
Energy traveling by waves
through empty space transfer
heat radiation transfer
Work, Force and Simple
Machines
What is Work
Anytime some object is moved some
distance, work is accomplished…if
A force is required to move that object
that distance
A force is a push or a pull in one
direction
Energy is required to create that force
Therefore, another definition of energy
is:
Energy is the ability to do work
What is Work
No matter how much effort is applied,
if there is no movement, there is no
work
There is also a requirement that the
movement is because of the effort
Therefore, the force must be in the
direction of the movement
Even if there is force applied, if it is
not in the same direction as the
movement, no work is done
Examples
Trying to unscrew a lid that won’t open
–No work is done
Carrying a bag a groceries in your arms
–No work is done
Picking up a feather
–Work done
Pushing a ant across a piece of paper
–Work done
The formula for work
The is an easy formula to find out
how much work is being done
Work is equal to the amount of force
being used multiplied by the distance
the object is moved
Work = Force x distance
What are simple machines
Simple machines are devices that allow
work to spread out over a longer
distance in exchange for a smaller force
Because work is equal to force x
distance, a longer distance multiplied by
a smaller force will mean the same
amount of work is done
Or a bigger force multiplied by a shorter
distance will mean the same amount of
work is done
How do simple machines work
By using a machine that moves a long
distance, the force needed to do work
will be less
A large wheel turns a greater distance
by is easier to turn than a smaller
wheel if both are attached to the same
load
A lever with a long arm is easier to
push or pull than one with a short arm
is they both are pushing the same load
More Examples
A screw with more turns on it is easier
to screw in than one with less turns,
even though it takes longer to screw in
A pulley that uses more rope is easier
to pull up than one that only uses a
small amount of rope
A long ramp is easier to walk up than a
short one even though it takes more
steps to do it
Which machine is easier to use
Vocabulary
Work – the force required to move an
object some distance
Lever – a beam or rod that rotates around
a fixed point called a fulcrum
Arm – the beam or rod of a lever
Fulcrum –fixed point that a lever turns
around
Wheel and axel – a large wheel that is
attached to a smaller wheel by a rod
Pulley – a kind of wheel that has a
groove hold a rope of cord that passes
over or under the wheel
Inclined plane – a slanted surface
Wedge – a moveable inclined plane,
also sometimes two inclined planes
placed together
Screw – an inclined surface that has
been wrapped around a cylinder
Electricity and Magnetism
Electricity and Magnetism are
caused by the same thing
Both electricity and magnetism have
the same beginning…movement of
electrons
Electrons are small particles that spin
or fly around the nucleus of an atom
In magnetism the direction of spin
sets up a field of energy around the
atom called a magnetic field
In electricity, free electrons moving
along a conductor causes electric
current
Magnetism
+
+
+
North pole
+
+
+
Magnetic Domain
+
+
South Pole
When the atoms all point in the same direction, a magnetic
field is produced called a domain which has a north pole and
a south pole
+
+
When the atoms point in different directions, no magnetic
field is produced
Electrical Current
Free
Electron
e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-
Electric current is the movement of electrons down a
conductor
Magnetism
Only three elements from the
periodic table of elements are
capable of producing magnetic
fields…iron, nickel and cobalt
These are known as the ferrous
metals from the Latin work for
iron…ferris
When a large enough number of
atoms of these metals are lined up
into a domain, the piece of metal is
Magnets
Magnets have a magnetic field
around them that has a north pole
and a south pole, just like the
domain around atoms
Magnetic energy leaves the south
pole of a magnet and circles around
and enters the north pole of that
magnet
N
S
Magnetic Attraction
Because magnetic energy leaves a
north pole and enters a south pole,
magnets act strangely around other
magnets
A north pole of one magnet will be
attracted to the south pole of
another magnet
A north pole of one magnet will be
repelled by a north pole of another
magnet
The Earth is a Magnet
Because of its very large iron-nickel core, the
earth acts like a very large magnet
The spinning of the liquid core sets up a
magnetic field around the earth with a
magnetic north pole and south pole
A compass reacts to the magnetic field of the
earth because it too is a magnet
The south pole of the earth attracts the south
pole of a compass because the south pole of a
compass is really… a north pole of another
magnet (the needle of a compass is a
magnet)
What’s this got to do with electricity
In the early 1800’s a Swedish
scientist named Hans Oersted
discovered that moving electricity
through a wire that had compass
near it made the compass swing
Something in the wire had changed
A magnetic field had been produced
in the wire… but by what?
He discovered that electrons moving
through a wire produce a magnetic
field
Cool…but so what, what good was it?
Oersted’s Discovery
Electric current
from a battery
causes a
magnetic field
around the
wire
Magnetism has everything to do
with electricity
A short time later an English scientist
named Michael Faraday discovered
just the opposite
He found that moving a magnet
through a coil of wire caused an
electric instrument to move
Somehow the movement of a
magnet caused electrons to leave
their atoms and travel to other
atoms…electric current
Faraday’s Discovery
Movement of a
magnet toward a
coil of wire
causes electric
current in the
wire
A new beginning for energy
Faraday’s discovery led to the
invention of both the electric motor
…the electric generator
A motor is a device that can use
electricity to produce mechanical
energy
A generator is a device that uses
mechanical energy to produce
useable amounts of electrical energy
Electricity generators
Because of Faraday’s discovery, it is
possible to create large amounts of
electricity
Generators are devices that contain
a magnet that rotates within a coil of
wire
The movement of the magnet causes
electrons to begin to move within the
wire
That movement of electrons is
Electrical Generator
Electricity Production
By connecting a generator to a power
source, electricity can produced
Wind power, hydro electrical power,
fossil fuel, and nuclear energy can
provide the energy to create electricity
Water is heated to steam by the above
energy sources
The steam turns a turbine that drives
the generator
How generators make electricity
Electric Motors
Electric motors are similar to generators,
but they have one major difference
Generators use mechanical energy to
turn a magnet inside a coil of wire
Generators use magnetism to create
electricity
Motors use electrical energy in a coil of
wire to create a magnetic field which
turns a magnet connected to the drive
shaft of the motor
Motors use electricity to create
Electric motor
Electric energy flows
from a power source
through the loop and
back to the power
source
_ +
Electromagnets
Magnetism created by electricity has
some advantages over permanent or
natural magnets
Electromagnets consists of a coil of
wire, a power source, and a piece of
ferromagnetic material (iron, nickel or
cobalt)
Electromagnets can be controlled –
they can be turned on and off
This allows them to be used in devices
such as door bells, telephones and
Electromagnet
Electric Circuits
When electricity is generated, it is sent
to do work
The pathway that the electricity
follows is called a circuit
Electricity must always return to its
source or into the ground or it will not
flow
Circuits have four parts; power source,
conductor, device, and a switch
(optional)
Electric Circuits
In an electric
circuit, the
pathway must
be complete
from the source
back to the
source to allow
electricity to
move through
the circuit
Series Circuit
If electricity
follows a single
pathway from
the source
through all of
the parts and
then back to the
source it is
called a series
circuit.
Series Circuit
If any part of a
series circuit
stops working,
the entire
circuit stops
working
Parallel Circuit
If electricity has
more than one
pathway that it
can follow from
the source
through all the
parts it is called
a parallel circuit
Parallel Circuit
If any part of the
circuit stops
working, the rest
of the circuit will
continue to work
Electricity can be transformed into
many other types of energy
Electricity can be used to
…toaster or room heat
Electricity can be used to create light as in a
…lamp
Electricity can be used to create motion as in a
…motor
Electricity can be used to create sound as in a
…radio or doorbell