Transcript ENERGY & POWER

ENERGY & POWER
Part 1
The Nature of Energy
What is Energy?
• The ability to do work or cause change is
called energy.
• OK…but what’s work?
• Work is done when a force moves an
object through a distance.
TYPES OF ENERGY
• The two types of energy are KINETIC &
POTENTIAL.
• What type you have depends on whether
an object is moving or not.
KINETIC ENERGY
• The energy of
motion is called
kinetic energy.
I
can’t
swim
!
What Affects Kinetic Energy?
• K.E. depends on an objects mass and its
velocity.
THINK: Which ball
would you have to push
harder to get rolling?
Once rolling the
bowling ball would
have more kinetic
energy than a golf
ball rolling at the
same velocity.
CALCULATING KINETIC ENERGY
• KINETIC ENERGY = MASS x VELOCITY2
2
Sometimes written (1/2)mv2
NOTICE: Changing the velocity of an object
will have a greater effect on its kinetic
energy than changing its mass. Why?
WHAT ARE THE UNITS?
• KINETIC ENERGY = MASS x VELOCITY2
2
K.E. = kg x m2
s2
instead of saying all that we use the Joule!
SAMPLE PROBLEM
• FIND THE K.E.
A 10 kg wagon moving at 5 m/s
• KINETIC ENERGY = MASS x VELOCITY2
2
10 x (5)2 divided by 2
10 x 25 divided by 2
250 divided by 2
.
125… what were those units? kg m2/s2 or JOULES
POTENTIAL ENERGY
• Potential Energy is energy that is stored
and ready to use.
TYPES OF POTENTIAL ENERGY
• ELASTIC –the energy of an object that is
stretched or compressed
GRAVITATIONAL POTENTIAL
ENERGY
• Potential Energy That Depends on Height
• G.P.E. = Weight (measured in Newtons) x
Height (measured in meters)
So..the units are NxM?
YUP!
Guess what? A NewtonMeter equals…
A JOULE!!!
Uh…Wait a second.
• What if I don’t know an objects weight in
Newtons?
• EASY: just multiply it’s mass (in Kg)
times the acceleration caused by gravity
(9.8m/s2)
Example: An object with a mass of 10kg
would weigh how many newtons?
RIGHT! 98 Newtons!
G.P.E. Sample Problem
• A hiker weighing 680 Newtons climbs up a
hill 40 meters high. How many Joules of
G.P.E. has the hiker gained?
G.P.E. = Weight x Height
680N x 40m= 27,200 Nm
-OR- 27,200 Joules!
DIFFERENT FORMS OF ENERGY
•
•
•
•
•
•
MECHANICAL
THERMAL
CHEMICAL
ELECTRICAL
ELECTROMAGNETIC
NUCLEAR
MECHANICAL
• The energy
associated with
motion or
position of an
object.
THERMAL
• The TOTAL energy of the particles in an
object (kinetic + potential).
CHEMICAL
• The potential energy stored in chemical
bonds that hold compounds together.
ELECTRICAL
• The energy of moving electric charges.
ELECTROMAGNETIC
• Energy That Travels in Waves.
NUCLEAR
• A type of potential
energy
• Stored in the nucleus
of the atom
• Released during
nuclear reactions
Part 1 Check for Understanding
1. Are energy and work the same thing?
Explain.
2. How are kinetic and potential energy
different?
3. List the forms of energy and give an
example of each.
4. A boulder the weighs 200N is sitting at
the edge of a 100m cliff. What is its
GPE?
• Work and energy are not the same thing,
even though they are measured in the
same units. Energy is the ability to do
work. As work is done, energy is
transferred from one object to another.
• Kinetic energy is the energy of motion.
Potential energy is stored energy; it has
the potential to do work.
• Mechanical – riding a bike
• Thermal – hot water
• Chemical – food
• Electrical – batteries
• Electromagnetic – TV Remote
• Nuclear – fusion in a star
• GPE = Weight x Height
• GPE = 200 N x 100 m = 20,000 J
ENERGY & POWER
Part 2
Energy Conversion &
Conservation
Part 2 Check for Understanding
1. What is energy conversion?
2. State the law of conversion of energy in your
own words.
3. Describe the energy conversion that occurs
when a ball is dropped and bounces back up.
Why does it bounce a little lower each time?
4. A roller coaster car with a mass of 500kg is at
the top of a hill that is 30 m high. Without
friction what would it KE be as it reached the
bottom of the hill?
ENERGY & POWER
Part 3
Energy Conversions & Fossil
Fuels
Part 3 Check for Understanding
1. How is the chemical energy in fossil fuels
related to the sun’s energy?
2. How is the energy of coal released?
3. Describe the energy conversions
involved in the formation of coal.
4. What general statement can you make
about the supply of fossil fuels? (Hint:
think about how they form).
ENERGY & POWER
Part 4
Power
Part 4 Check for understanding
1. State the formula for calculating power.
2. How are power and energy related?
3. Find the work you do when you exert a
force of 40N to run a distance of 18m in
4 seconds. Now find the power you used.
4. The motor of an electric fan converts
24,000 J of electric energy every 60 sec.
What is the power of the fan’s motor?
ENERGY
KINETIC
ENERGY
ELASTIC
POTENTIAL
ENERGY
GRAVITATIONAL
JOULES
WORK
POWER