2. Most people say that they do work when they
wash clothes,clean the house,weed the garden
or do other activities except rest or play.To a
scientist,work has a diferent meaning .Find out
what work is according to scientist.
3. To a scientist,you have done work when
the force you applied on the chair moved
it from one another to place.You have not
done work when the force youapplied on
te wall did not move it at all.It is not only
people who can do work. Machines can
also do work.Machine have the force that
can make objects move.
Main idea: work is done when a force applied on
an object moves tha the object from one place to
another in the same dirction as the force.
4. What is energy
Try to throw a ball up n the air nd catch it. Do this
several times.What made the ball move through the
air? You have energy.This energy moved your arm to
exert force on the ball.Because the ball moved,you
have done work.Do you think this could happen if
you had no energy.
5. Suppose you continued throwing and
catching the ball for an hour,what do you
think would happen?Of course you would get
tired because youused up the energy stored
in your muscles.Without energy,ou could not
have the force needed to move the ball.You
need energy.This is the reason you eat and
rest.You need energy to move about and do
work
6. The two kinds of Energy
The two kinds of energy are POTENTIAL and KINETIC
energy.Potential is stored energy. Potentialmeans “having
power”. The potential or stored energy can be used in the
future.
7. Forms of Potential energy
The forms of potential energy are.....
Chemical energy
Elastic energy
Gravitational energy
8. Chemical energy is the form of potential
energy stored in substances.For example
food,wood and coal have chemical
energy.Chemical energy can be released
through a chemical change.Thus,the chemical
energy of food is released by chemical changes
including digestion and formation of a high-
energy compound that we call ATP.ATP is the
immidiate source of energy for everything we
do.Similarly,the chemical energy of wood or coal
is released by burning it.We use this energy for
cooking food and for many other purposes.
9. Elastic energy
Elastic energy is the energy stored in elastic
materials
such as a spring and a strip of a rubber.Have you
seen a “jack in the box”?It is a gift box that is
intended to surprise the oonewho receives the
gift.When you open the box,a toy clown jumps out!
The base of the toy clown is a commpressed
spring,a coiled wire.Opening the box releases the
elastic energy of the spring.
10. gravitational energy
Gravitational energy is the energy posessed
by an object because of the pull of
gravity.This is the energy possesed by the
object asa result of its position.Thus,when
you are standing at the top of the stairs,your
potential energy is a greater than when you
are standing closer to the foot of the stairs.
If you fall from the top of the stairs,the force
of your fall will be greater than if you fall from
close to the floor level.
11. The energy that a moving object posseses is
called kinetic energy.The word kinetic comes
from the greek word “kinetos”,which means
“moving”.
15. TRANSFORMATION OF ENERGY
Energy is never created or lost.It just changes
from one another.This is called
transformation.Find out how potential energy is
transformed into kinetic energy
16. MAIN IDEA
Potential energy is stored that can be used in
the future.Kinetic energy is the of a moving
object.
