Transcript WORK DONE & ENERGY

WORK DONE & ENERGY
Produced by
Tsang Siu Chung
Work done
• In everyday language,work may mean anything
that people do.
• In science,it is given a more precise meaning:
work is done whenever a force
moves an object.
Work = forcedistance moved in the
direction of the force
W=Fs
W=Fs
F
F
s
W = F s cos 

F

F
s
Work is measured by newton
metre (N m)
Joule ( J )
Important definition
1 joule of work is done when
a force of 1 newton moves a
distance of 1 metre in the
direction of the force.
Energy
• Things have energy if they can do
work.We can think of energy as a
capacity for doing work in the future.
• Energy ,like work, is measured in
joule(J).
BOB!
Now,we will talking about the
mechanical energy.
The followings are different forms of mechanical energy.
• Kinetic energy
• Gravitational potential
energy
• Strain energy
Kinetic energy
• A moving object has kinetic
energy.
• The faster it moves the more
energy it possesses.
• When a human run,chemical
energy from the food changed
into kinetic energy.
Gravitational potential energy
• When you lift a box up , it
gains gravitational potential
energy.
• The higher the box the more
gravitational potential energy it
possesses.
• If the box falls down , its
gravitational energy is changed
into kinetic energy.
BOX
Gain
gravitational
energy
BOX
Strain energy
• Another form of potential
energy.
• It is energy possessed by an
elastic object when it is
stretched , compressed or
bent.
• If the elastic is released , its
strain energy is changed into
the kinetic energy.
Energy change and work
• Work is done whenever energy is transferred
from one from to another.
Work done = Energy transferred
Example:
If a falling stone loses 10 joules of gravitation
potential energy and gains 10 joules of kinetic
energy , the gravitational force acting does 10
joules of work in accelerating the stone.
Energy in one form
Work is done
Energy in another form
This is the end of my project . I hope
that you will have a general idea about
Thank you.
THE END