Transcript energy - SchoolRack

ENERGY
Forms and Conservation
Nature of Energy
Energy is all around you!
• You can hear energy as sound.
• You can see energy as light.
• And you can feel it as wind.
What is Energy?
Energy is
the
ability to
do work.
If an object or organism
does work (exerts a
force over a distance to
move an object) the
object or organism uses
energy.
Work is a
transfer of
energy.
An object
that has
energy has
the ability to
do work.
Because of the
direct connection
between energy
and work, energy
is measured in
the same unit as
work: joules (J).
1 joule = 1
newton
meter
KINETIC ENERGY
 Kinetic
Energy
is the energy
of motion.
http://www.youtube.com/watch?v=I
GQ5lkVHPwc
An object
must be in
motion to have
kinetic energy
KINETIC ENERGY


The faster an
object moves, the
more kinetic
energy it has.
Kinetic energy
depends on both
mass and velocity.

The greater the mass
of a moving object,
the more kinetic
energy it has.
K.E. = ½
2
m𝑣
CALCULATIONS
A 50kg boy went jogging with his father.
Both ran at a velocity of 5m/s. Find out the
kinetic energy of the boy.
K.E. = ½
1
2
50 kg
2
m𝑣
=
5m 2
s
Now let’s try to figure
out the father’s kinetic
energy if he has a mass
of 100kg.
625 (kg x m2/s2)
or 625 J
1250 J
POTENTIAL ENERGY

Potential Energy is
stored energy as a
result of position or
shape.

Stored chemically in
fuel, the nucleus of
atom, and in foods.

Or stored because of the
work done on it:

Stretching a rubber band.



Winding a watch.
Pulling back on a bow’s arrow.
Lifting a brick high in the air.

GRAVITATIONAL
POTENTIAL ENERGY
Potential energy that is dependent on
height is called gravitational potential
energy.

A waterfall, a suspension
bridge, and a falling
snowflake all have
gravitational potential
energy.


GRAVITATIONAL
POTENTIAL ENERGY
An object’s gravitational potential energy (GPE)
depends on its mass, height., and acceleration
due to gravity.
I. E. If you stand on a 3-meter diving board, you
have 3 times the G.P.E, than you had on a 1meter diving board.
PE = mgh
G stands for
acceleration due to
gravity.
It’s value is 9.8 m/s2
CALCULATIONS
What is the potential energy of a 10 kg
book that is placed on a shelf that is 2.5
meters high?
PE = mgh =
2
10 𝑘𝑔 (9.8 𝑚/𝑠 ) (2.5 m)=
Remember g is the
acceleration due to
gravity a constant
always equal to 9.8
m/s2
245 J
ELASTIC
POTENTIAL ENERGY

Energy that is stored due to being
stretched or compressed is called elastic
potential energy.
FORMS OF ENERGY
All energy can be classified as
kinetic, potential or the energy
fields such as electromagnetic.
The major forms are:
• Mechanical
• Thermal
• Chemical
• Electrical
• Electromagnetic
• Nuclear
MECHANICAL ENERGY

• Energy
associated with
the motion and
position of
objects.
• Sum of an
object’s kinetic
and potential
energy.
When you kick a
football, you give
mechanical energy
to the football to
make it move.
Bouncing ball
THERMAL ENERGY
The internal motion of the atoms is called
thermal energy, because moving particles
produce heat.
 Thermal energy can be produced by friction.
 Thermal energy causes changes in
temperature and phase of any form of
matter.
 Fire

CHEMICAL ENERGY
 Energy
Stored in chemical bonds.
 Chemical Energy is required to bond
atoms together.
 And when bonds are broken, energy is
released.
 Fuel and food are forms of stored
chemical energy.
 Wood, gas, food
ELECTRICAL ENERGY
• Associated with Electrical Charges.
• Batteries convert chemical energy
into electrical energy that you then
use to power your small appliances.
• Lightning is an example of electrical
energy.
ELECTROMAGNETIC ENERGY





Form of energy that travels through space as
waves.
Power lines carry electromagnetic energy into your
home in the form of electricity.
Light is a form of electromagnetic energy.
Each color of light (Roy G Bv) represents a
different amount of electromagnetic energy.
Electromagnetic Energy is also carried by X-rays,
radio waves, and laser light.
NUCLEAR ENERGY
The nucleus of an atom is the source of
nuclear energy.
 When the nucleus splits (fission), nuclear
energy is released in the form of heat
energy and light energy.
 Nuclear energy is also released when nuclei
collide at high speeds and join (fuse).

Energy Conversion
Energy can be
changed from one
form to another.
Changes in the
form of energy are
called energy
conversions.
Energy conversions
All forms of energy can
be converted into other
forms.
The sun’s energy through solar
cells can be converted directly
into electricity.
Green plants convert the sun’s
energy (electromagnetic) into
starches and sugars (chemical
energy).
Other energy
conversions
In an electric motor, electromagnetic
energy is converted to mechanical
energy.
In a battery, chemical energy is
converted into electrical energy.
The mechanical energy of a waterfall
is converted to electrical energy in a
generator.
Energy Conversions
In an automobile
engine, fuel is
burned to convert
chemical energy into
thermal energy. The
thermal energy is
then changed into
mechanical energy.
Chemical  Thermal Mechanical
Kinetic-Potential Energy
Conversion
Roller coasters work
because of the energy that
is built into the system.
Initially, the cars are pulled
mechanically up the tallest
hill, giving them a great deal
of potential energy. From
that point, the conversion
between potential and
kinetic energy powers the
cars throughout the entire
ride.
Kinetic vs. Potential Energy
At the point of
maximum potential
energy, the car has
minimum kinetic energy.
Kinetic-Potential Energy
Conversions
As a basketball
player throws
the ball into
the air,
various
energy
conversions
take place.
Ball slows down
Ball speeds up
The Law of Conservation of
Energy
It can only be converted from one form to another.
If energy seems to disappear, then scientists look
for it – leading to many important discoveries.
(PE + KE) beginning =
(PE + KE) ending
Energy can be
neither created
nor destroyed
by ordinary
means.
The Law of Conservation of
Energy
In 1905, Albert Einstein
said that mass and
energy can be
converted into each
other.
He showed that if
matter is destroyed,
energy is created, and
if energy is destroyed
mass is created.
E = MC2