WEEK 9
SUBJECT: BASIC
SCIENCE
CLASS: GRADE 8
TERM: SECOND
TOPIC: WORK,
ENERGY AND POWER
MEANING OF WORK
AND ENERGY:
WORK: Work is said to
be done when a force tends to move an object upon which it acts on a certain
distance. Work is also said to be done if the force applied on a body changes
its position, speed and changes its direction of motion. Work can be physical
for example carrying a load, ploughing a field or jogging, or mental for
example writing, thinking or reading. In physical science, we recognize only
physical or mental work and also if there are some displacements, i.e. the body
has moved from one place to another. In science, we do not recognize mental
work as work done, although it also consumes energy.
Example: When a crane
picks up a car involved in an accident and takes it to a workshop, we say that
work is done.
Derivation of
work: Work
is said to be done when a force moves an object through a distance in its own
direction. The amount of work done depends upon the force applied (magnitude)
and the displacement of the object. Work= Force*Distance OR W=F*S
Unit of work: The unit of work
is therefore the product of a unit of force and a unit of distance. Since the
unit of force is newton (N) and the unit of distance is metre (m), therefore
the unit of work is newton-metre (Nm). A newton-metre is also called a joule.
Unit
of work = 1 Newton* 1 metre
=1Nm
=1
Joule
1KJoule=
1000J
CALCULATIONS
INVOLVING WORK DONE:
1.
If a boy lifts a textbook weighing 10N from the floor to a table of heit 2m,
how much work does he do?
Solution:
Work
done= Force*Displacement
= 10N*2m= 20J
MEANING OF
POTENTIAL AND KINETIC ENERGY:
Energy
is the ability to do work. Energy has neither mass nor does it occupy any space
yet it exists in many forms. To do more amount of work, we need more amount of
energy. After doing sufficient amount of work, one feels tired because lots of
energy has been used up during this process. So we say, there is a direct
relationship between work and energy. The unit of energy is Joule (J) which is
the same as that of work. Different forms of energy include: Kinetic,
Potential, Sound, Light, Electrical, Heat, Chemical, Magnetic Energy. The energy
possessed by a body due to its state of rest or state of motion is called mechanical energy. Mechanical energy is
of two forms: Kinetic energy and Potential energy.
Kinetic Energy: The energy that
the moving bodies possess is called kinetic energy. Examples of kinetic energy
are running water, swinging pendulum, moving air and moving bus. Bullet are
capable of penetrating into thick sheets of metal, storm can uproot big tree
all because of the high speed which increases the kinetic energy of the bullet
or air by a very large amount.
The formula for
kinetic energy is K.E. =1\2MV2
The unit is
joule
Potential
Energy: Stored
up energy is called potential energy. It means that the energy is inactive at
the moment but has the potential for doing work. For examples, when we wind up
the spring of an alarm clock, our muscular energy gets stored in its spring. It
is this energy which is slowly released and moves the hand of a clock. Examples
of potential energy are water stored high up in dams, a ball kept on a table, a
stretched or compressed spring, etc.
The formula for
potential energy is P.E. = m*g*h
The unit is
joule
ASSIGNMENT
1.
Explain work done.
2.
State the formula and unit of work done.
3.
Differentiate between kinetic and potential energy.
4.
State the formula for kinetic and potential energy.
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