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SUBJECT: Physics TEACHER: Mr. S. CampbellDATE: GRADE: 12-13DURATION: 1 wk GENERAL TOPIC: Work, Energy And Power
Work And Energy
On completion of this section, you should be able to:
● Identify various forms of energy● State the principle of conservation of energy● Describe examples of energy conversion● Define Work
Energy is the capacity or ability to do work
The SI Unit of energy is Joules (J)
Various Forms of Energy
● Mechanical (includes kinetic and potential)● Electrical● Chemical● Thermal● Nuclear● Solar
Group Discussion
Why has it been determined and established that the sun is the primary source of energy?
Example Energy Conversion
An incandescent bulb being switched on
Electrical Energy to light and heat
A book falling from a shelf to the floor Gravitational potential energy to kinetic energy and sound energy
A battery Chemical energy into electrical energy
A hydroelctric plant Gravitational potential energy into kinetic energy and then into electrical energy
A catapult being released Elastic potential energy into kinetic energy
Renewable Sources of Energy are sources of energy that are derived from natural sources, e.g wind, sunlight, waves, hydroelectric, geothermal etc. These sources are replenished over time.
Group Discussion
When considering how energy is used in Jamaica, what do you think would be the top 3 renewable/alternative sources of energy that could be used?
As a guide, compare main features, advantages and disadvantages of each.
When Work is done by a force, it is the product of the force and the distance moved in the direction of that force.
The SI unit of Work (like Energy) is Joules (J)
W = Fs1J = 1Nm
Energy And Power
On completion of this section, you should be able to:
● Distinguish between kinetic and potential energy● Derive the formula for kinetic energy● Derive the formula for gravitational potential
energy● Define Power● Appreciate the concept of efficiency
The kinetic energy of a body is the energy possessed by virtue of its motion.
An object of mass, m, moving with a velocity v has a kinetic energy of:
Ek =
1mv2
2
s
v
F
The potential energy of a body is the energy it possesses by virtue of its state or position.
Ep = mgh
W = mg
h
Power is defined as the rate at which work is being done.
The SI unit of power is the watt (W)
P =W
t
P = Fv
P =F x D
t
Since v =d
t
