Transcript Chemical energy - Cloudfront.net

Objective 4
Energy, Forces, and Motion
Middle School Science
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Energy
The ability to do
work or to cause
change
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Chemical Energy –
Energy transformations
Chemical energy – when light energy from the sun is converted to the
energy in the bonds of the sugar molecules formed in photosynthesis.
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Chemical Energy
Examples of chemical
energy changing into
heat energy:
Lighting a match
Burning a wood fire
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Heat energyEnergy transformations
Heat energy –
energy is absorbed
and temperature
rises.
Specific heat- the
ability of a substance
to absorb heat
energy
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Electrical energyEnergy transformations
Electrical energy- flow of electrons (a current)
Other ways of generating electricity:
•Water flowing through a dam in a river to move
turbines
•Wind generators that use the energy of moving
wind & operate a generator
•Nuclear power plants convert atomic energy into
heat. Heat boils water to form steam & then
follows the same energy transformations as coal
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power plants Science TAKS Need to Know
Many energy transformations…
Electrical to mechanical:
Electricity used to spin the CD (Spinning CD has mechanical energy due
to its position or motion)
Electrical to sound:
A laser converts the digital information on the CD into electrical energy and
this energy goes to the headphones as a vibration- this transmits Sound!
Chemical to electrical:
Batteries store chemical compounds that react when they are used to
power something. This produces a flow of electrons which is electricity!!
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Sound energyEnergy transformations
Sound – consists of mechanical
energy waves created by vibrations.
Sound must travel through
something (called “medium” or
“media”) such as air, water, or a
solid.
The medium carries the energy of
the wave from one place to another.
Example: Air transmits the energy
of the vibrating material in the
headphones to your eardrums.
A vacuum is a space that contains little or no matter. Sound can’t
travel through a vacuum since there are no particles to squeeze
together (compression) or spread apart (rarefaction)
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Many times it takes a whole series of energy conversions to do a certain job.
For example, just to get the energy to make a piece of toast, there are several
energy conversions involved.
Chemical energy stored in coal is released as heat and light energy when the coal
is burned. The heat energy is used to produce steam and is changed into
mechanical energy in a generator. The generator converts mechanical energy into
electrical energy that travels through power lines into your home. When you use
your toaster, that electrical energy is again changed into heat energy.
Have you ever touched a light bulb when it was on? Or tried to change it when it
burnt out after being on? What you have discovered is the conversion process of
energy- When you turn on a light, not all of the electricity is converted to light
energy. Some of the energy is converted to heat.
Remember, energy is never lost- it’s only converted from one form to another.
This is the law
of conservation of energy
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Light waves do not
need a medium to
transmit energy! They
can even travel through
empty space.
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A wave is a disturbance that
transfers energy from one place
to another.
Water waves are
a form of a wave
that transmits
mechanical
energy across
the surface of
water.
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Seismic waves are caused by
earthquakes that transmit
mechanical energy through the
Earth’s layers.
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Potential (PE)
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Before the yo-yo begins its fall it has stored energy due to its
position. At the top it has its maximum potential energy. As it
starts to fall the potential energy begins to be changed into kinetic
energy. At the bottom its potential energy has been converted
into kinetic energy so that it now has its maximum kinetic energy
A waterfall has both potential and
kinetic energy. The water at the top
of Bridal Veil Falls has stored
potential energy. When the water
begins to fall, its potential energy is
changed into kinetic energy.
This change in energy also
happens at Niagara Falls where it
is used to provide electricity from
the transformation of mechanical
and electromagnetic energy.
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Kinetic Energy (KE)
Energy due to
motion of an object
Did you know that
the gas burned in a
car engine is
chemical energy
being turned into
Kinetic Energy?
Rubber band flying
through the air has
kinetic energy
Speed & mass affect
kinetic energy–
Faster/heavier…more
Kinetic Energy
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Energy Transformations
Potential energy
A rock sitting at the
top of a cliff
Roller coaster car at
the top peak of a
hill
A swimmer posed to
dive off the end of
a diving board
NO MOTION !!
Kinetic energy
A bouncing ball
A moving roller
coaster
A track star
running
A girl skiing
MOTION is the
key!!!!
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You use force to move your body
When you bend your arm, your
muscles contract, which
applies force to your arm
bones. Your arm responds to
this force by moving.
During breathing, muscles
contract (use force) to move
air in and out of the lungs.
The heart contracts
(uses force) to pump
blood through the
blood vessels,
carrying oxygen to the
muscles.
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All living things use force to move
Emerging seedlings
exert force on the
surrounding soil.
This force pushes
the stem of the plant
out of the ground.
Plants exert
force to open
flower petals,
curl & uncurl
leaves &
push roots
through the
soil.
Force is used to
move materials
in & out of cells.
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Fish exert force to
swim by pushing
against the water.
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In order for a force to move something, it must be
an unbalanced force. This means that a force is
stronger in one direction than the forces in the
opposite direction.
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Speed involves distance & time
Average speed – can be calculated by dividing total distance by
total time.
S= D/T
Instantaneous speed – an object’s speed at a specific moment
When instantaneous speed does not change, an object is moving
at constant speed; in this situation average speed and
instantaneous speed are the same.
Speed and direction of motion is velocity.
Acceleration is the change in velocity divided by the time it takes
for the change to happen. It can be a change in speed or a
change in direction or both. Acceleration can be calculated using
this formula: a = ( final speed - initial speed )
time
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Acceleration can be shown on a speed-time
graph.
A change in speed is a change in velocity – so,
a change in speed is an example of
acceleration! Acceleration may be positive or
negative. Negative acceleration is sometimes
called deceleration.
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Data can be
displayed &
interpreted in many
ways
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The energy transferred when a
force moves an object or changes
its shape
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Newton’s 1st law – states an object at rest will
stay at rest unless acted on by an unbalanced
force. An object in motion will stay in motion at
the same speed and direction unless acted on
by an unbalanced force.
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- a moving object moves in a straight line with constant speed
unless a force acts on it.
- An object will not start moving unless a force acts on it
- An object will not stop moving unless a force acts on it
- An object will not change speed unless a force acts on it
-An object will not change direction unless a force acts on it 30
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2nd law states that the acceleration of an
object depends on its mass and the size
and direction of the force acting on it.
Acceleration can be calculated as
Acceleration = force/mass
~or~
Force = mass X acceleration
The more mass an object has the more force it takes to cause
acceleration.
- Big masses are hard to accelerate.
- Small masses are easy to accelerate.
- Objects accelerate more quickly when a greater force is
used.
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