Force, Motion and Energy
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Section 1
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What is Energy?
Energy is the ability to do work or cause
change.
Examples: When the wind moves
a leaf, or picks up a house.
In this case, the change is in the
position of the
object, so the
wind has energy.
Work is done when a FORCE moves an OBJECT some
DISTANCE.
When an object or
organism does work
on an object, some of its
ENERGY is transferred to that object. So WORK
could be
thought of as THE
TRANSFER OF ENERGY. When energy is
transferred, the object upon which the work is done
GAINS
energy.
Energy is measured in
units called JOULES.
One
JOULE (J) is the amount of work you do when you exert
a
force of one NEWTON to move an object a distance of one
METER.
One
NEWTON is the amount of force required to accelerate
one
kilogram of mass at 1 meter per second.
1 N = 1kg X 1m/s
There are two general kinds
of Energy
Kinetic
Energy
and Potential Energy
Whether the energy is Kinetic or Potential depends on whether
the energy is being TRANSFERRED OR STORED.
KINETIC
ENERGY: This is the energy of motion. Because the
object is
MOVING it is doing work,
therefore it has ENERGY.
The word “Kinetic” comes
from the Greek word KINETOS, meaning
“moving”.
The Kinetic Energy of an object depends on both its MASS
and its VELOCITY
“MASS” the amount of matter in
an object
“VELOCITY” speed in a given
direction.
“SPEED” the distance an object
travels in one unit of
time.
Think about rolling a golf ball and a bowling ball so
that they travel
at the same
velocity. Which ball would you have to roll more
forcefully? You
would have to exert a greater force on the
bowling ball because it
has a greater mass than the golf ball.
Since energy is
transferred during work, the more work you do, the
more energy you give to
the ball. So, a bowling ball has more
KINETIC ENERGY than a
golf ball traveling at the same velocity.
KINETIC ENERGY INCREASES
AS MASS INCREASES
KINETIC ENERGY ALSO
INCREASES AS VELOCITY INCREASES
(because you would have to do more work on the bowling
ball to
give
it a greater velocity)
So KINETIC ENERGY depends on both MASS AND VELOCITY
Potential Energy
Sometimes
when
you transfer energy to an object, you change its position or
shape.
For example: you lift a book up to a shelf, or you compress a
spring to wind a toy.
Unlike
Kinetic
Energy, which is the energy of motion, Potential Energy is stored.
Energy
that
is stored and held in readiness is called POTENTIAL ENERGY.
This type of energy has the POTENTIAL to do work. Just like
you people!
Examples of Potential Energy:
An archer gives potential energy to a bow
by pulling it back. This stored
energy can send an arrow flying towards its
target.
The potential energy associated with
objects that can be stretched or
compressed is called ELASTIC POTENTIAL
ENERGY.
POTENTIAL ENERGY that depends on height is
GRAVITATIONAL
POTENTIAL ENERGY.
You might give this type of
potential energy to an object when you lift it.
The GRAVITATIONAL
POTENTIAL ENERGY of an object is
equal
to the work done to lift it.
The greater the weight of an object, or the greater height it
is lifted, the greater the gravitational potential energy.
How could the hiker
have gained MORE gravitational potential energy?
OTHER FORMS OF ENERGY
Kinetic
and
Potential Energy involve objects being moved or physically
changed.
Both kinetic energy and potential energy have a variety of
different forms.
Some
of
the major forms of energy are :
MECHANICAL
ENERGY,
THERMAL ENERGY,
CHEMICAL ENERGY,
ELECTRICAL ENERGY,
ELECTROMAGNETIC ENERGY
AND
NUCLEAR ENERGY.
MECHANICAL
ENERGY- This is energy associated with the motion or
position of
on object. Mechanical energy can occur as
kinetic energy OR potential energy
THERMAL ENERGY- This is the total energy of the
particles in an object. When
the thermal energy increases, the particles move
FASTER, making it feel
warm to the touch. The particles have both
potential and kinetic energy
due to their arrangement and motion.
CHEMICAL
ENERGY- This is potential energy stored in chemical bonds
that
hold chemical compounds together. Chemical
energy is stored in the foods
you eat, and in a match used to light a candle, and
even in the cells of your
body.
ELECTRICAL
ENERGY- Moving electrical charges produce electricity or
electrical
energy. We rely on electrical energy from
batteries and power lines to run
electrical devices such as radios, TVs, lights and
computers.
ELECTROMAGNETIC
ENERGY- Electromagnetic Energy is energy that travels
in waves. These waves have some electrical
properties and some
magnetic properties. Some examples of
electromagnetic energy are:
visible light, ultra violet radiation, microwaves, and
infra red radiation.
NUCLEAR
ENERGY- This is a type of potential energy stored in
the nucleus of
an atom. One kind of nuclear energy occurs when
a nucleus splits
(nuclear fission) and another occurs when nuclei fuse
(fusion). Power plants
use fission to produce energy. Fusion occurs in
the sun and other stars, as
well as in nuclear bombs.
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Section 2
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Energy Conversion and
Conservation
A
change from one form of energy to another is called ENERGY
CONVERSION or
an ENERGY TRANSFORMATION.
Any
form
of energy can be converted
into any other form
Examples:
Toaster: Converts
electrical energy into thermal energy.
Electric Motor:
electrical energy converted to mechanical energy
Your Body-converts
chemical energy in the food you eat into the mechanical
energy
you need to move your muscles. Chemical energy in your
body
is
also converted to the thermal energy your body uses to
maintain its
temperature. Chemical energy is also converted
into the electrical energy
your
brain uses to think.
OFTEN, A SERIES OF ENERGY
CONVERSIONS ARE NEEDED TO DO A TASK.
Example:
A match: Strike a
match and the mechanical energy needed to move the match is
converted to thermal energy. The thermal energy
causes the match to
release the stored chemical energy, which is converted
to thermal energy,
and
then to the electromagnetic energy you see as light.
A car engine: Electrical
energy produces a hot spark. The thermal energy of the
spark releases the chemical energy of the fuel. When the
fuel burns, the chemical energy turns into thermal
energy. Thermal energy is converted into mechanical
energy used to move the car, and to electrical energy to
produce more sparks
Energy cannot be created OR destroyed,
but it can change form!
(This is
much more important than it sounds, try
and remember it! Trust me!)
THE
LAW OF
CONSERVATION
OF ENERGY-
when one energy form is converted into another, NO
ENERGY is destroyed in the process. Energy cannot
be created OR destroyed
Thermal
Energy:
The total
energy of all the particles in a substance is called Thermal
Energy. Even if two samples of matter are at the same
temperature, they do not necessarily have the same Thermal
Energy. The more particles a substance has at a given
temperature, the more thermal energy it has.
Heat- is the movement of
thermal energy from a substance at a higher temperature to
another at a lower temperature. (Heat is thermal energy moving
from a warmer object to
a cooler object)
Heat
Transfer always occurs with heat moving to substances with
less heat. The heat flows from the warmer substance to
the colder one.
How
is
heat transferred?
There
are
three ways that heat can move. Conduction, Convection
and Radiation
CONDUCTION- In this
process, heat is transferred from one particle of matter to
another particle of matter without the movement of the
matter itself.
CONVECTION- In this
process, heat is transferred by the movement of currents
within a fluid (a liquid
or a gas).
CONVECTION CURRENTS- formed when hot things rise and
cooler things
sink.
RADIATION- This is the
transfer of energy by electromagnetic waves. Radiation
does not require matter to transfer the thermal energy.
This is a big difference, and an important one.
CONDUCTORS AND INSULATORS
Conductor- a
material that conducts heat well.
Metals are good
conductors of heat.
Insulator- A material
that does not conduct heat well.
Wood, wool, straw, paper,
cork, are all good insulators.
House Insulation:
Prevents heat from leaving the building in cold weather, and
prevents heat from
entering the building in hot weather.
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Section 3
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FORCE AND MOTION
GRAVITY-the
force
of attraction between object with MASS.
On Earth, it is the force that pulls objects towards Earth.
The LAW OF
UNIVERSAL GRAVITATION states that the force of gravity acts
between all objects in the universe. ANY two objects in
the universe, without exception, attract each other.
YOU
are
attracted to the Earth, but the Earth is also attracted to
you.
Also, every object around you are also attracted not
only to the Earth, but also to YOU.
Gravitational
Force
depends on MASS. The force also depends on the DISTANCE
between the objects.
The farther apart the objects are, the weaker the
gravitational force between them.
Remember
the
difference between MASS and WEIGHT.
Mass is a measure of the amount of matter in an object.
Weight is a measure of the force of gravity upon an object.
Motion
It's often difficult to
tell if an object is in motion. Right now, as you’re
sitting in class, aside from your eyes blinking and your chest
moving, and your head occasionally slamming forward on your
desk, you probably would say that you are not moving.
An object is in motion
when its distance from another object is changing. Since
the distance between you and me isn’t changing, you conclude
that you’re not moving.
At the same time you're
sitting there, you're actually moving at about 30km/sec.
At that speed, you can travel from NYC to LA in about two
minutes! You’re moving this fast because you’re sitting
on planet Earth, which is orbiting the sun. Earth moves
30 km every second in its path around the sun.
Whether or not an object
is moving depends on your point of view.
A REFERENCE POINT is a
place or object used for comparison to determine if something
is in motion. An object is in motion if it changes its
position relative to a reference point.
SPEED
SPEED
IS
THE DISTANCE AN OBJECT TRAVELS IN ONE UNIT OF TIME.
VELOCITY-
It's
not just another word for speed.
Velocity
is
speed in a given
direction.
ACCELERATION
Acceleration
is
the RATE AT WHICH VELOCITY CHANGES.
In
science,
ACCELERATION refers to INCREASING speed, DECREASING speed, or
CHANGING DIRECTION.
It doesn't must mean "speeding up".
Force
A
FORCE IS A PUSH OR A PULL
The Force is Strong in this one...
Forces
are
described by not only how strong they are, but also by the
direction in which they act.
Unbalanced Forces: Objects may have a variety of forces
acting upon them.
When these forces are balanced, the
object doesn’t move.
When the forces are UNBALANCED,
movement can happen.
Forces can ADD together and combine.
Forces can work in opposite
directions and subtract.
If one force is greater than the
other, the overall force
is in the direction of the greater
force.
The overall force on an object after
all the forces are added
or subtracted is called the
NET FORCE.
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Section 4
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Newton's Laws of Motion
Newton's First Law states that
objects in motion will stay in motion unless acted upon by
an outside force,
and objects that are NOT moving will continue NOT moving
unless acted upon by an outside force.
This property is called Inertia.
Newton's Second Law explains how the velocity of an object
changes when it is subjected to an external force.
For an object with constant mass (m), the second law
states that the force (F) is the product of an object's
mass
and its acceleration (a). The formula is F=m*a
(Force is equal to mass times acceleration) Force
increases when
you speed up, or increase mass. If you want to hit a
baseball and make it travel farther, you either need to
swing
the bat faster, OR, use a heavier bat.
Newton's Third Law states that for every action (force),
there is an equal and opposite reaction (force).
When you step into a boat and apply your 100 lbs of force
to the bottom of the boat, the boat
pushes up with the same amount of force. The same
thing happens when you stand on a floor,
but it's easier to feel in a boat. When you first
step in, the boat moves downward, then rebounds back
up.
