Download Lesson 2 energy diagrams, potential e..

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1 Energy Types Word Scramble
2 Title – Energy Flow diagrams
and the date
Some examples of forms of energy
Kinetic energy (KE)
Nuclear energy
Energy due to a body’s motion.
Energy associated with nuclear
reactions.
Potential energy (PE)
Energy due to a body’s position
Electrical energy
Thermal energy
Energy associated with electric
charges.
Energy due to a body’s
temperature.
Chemical energy
Energy associated with chemical
reactions.
Elastic energy
Energy stored in an object when it
is stretched or compressed.
All of the above forms of energy (and others) can
ultimately be considered to be variations of kinetic or
potential energy.
Learning Today
•
•
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Energy flow diagrams
Energy flow circus
Sankey diagrams
Potential Energy – P.E.
Homework Potential Energy Sheet
Other energy measurement examples
4200 joules (4.2 kJ) 1 food Calorie
1 000 000 J (1 MJ) Energy of a Mars bar
0.000 02 J
Energy need to produce a
syllable of a word
15 000 000 000 000 Energy received by the Earth
from the Sun in one day
000 000 000 J
Conservation of energy
Energy cannot be created or destroyed. It can
only be transformed from one form to another
form.
Conservation of energy also means that the total
energy in the universe stays constant.
Energy Flow diagrams –
Copy please
Energy flow diagrams show energy
transformations.
Work done = energy transformed
For example, when a car brakes, its kinetic energy is
transformed into heat energy in the brakes.
Kinetic
heat
Energy changes
22/05/2017
To describe an energy change for a
light bulb we need to do 3 steps:
1) Write down the
starting energy:
3) Write down
what energy types
are given out:
2) Draw an arrow
Electricity
Light + heat
Draw energy flow diagrams for the following…?
1) An electric fire
2) A rock about to drop
3) An arrow about to be fired
Television
What are the main energy transfers for a television
(don’t forget the wasted energy)?
light
electrical
sound
heat
Car engine
What are the main energy transfers for a car engine
(don’t forget the wasted energy)?
kinetic
chemical
sound
heat
Radio
What are the main energy transfers for a radio
(don’t forget the wasted energy)?
sound
electrical
heat
Pendulum oscillation
GRAVITATIOINAL POTENTIAL
MINIMU
ENERGY MAXIMU
MM
KINETIC
MAXIMU
ZER
ENERGY
MO
The total energy, gravitational
potential plus kinetic, remains
the same if there are no
significant resistive forces
Wasted sound energy
Can you name some devices that waste energy as sound?
Hairdryer
_____________
Washing
machine
_____________
Car engine
_____________
Computer
_____________
Microwave
_____________
Bunsen burner
_____________
Wind turbine
_____________
Dish washer
_____________
Wasted heat energy
Can you name some devices that waste energy as heat?
Radio
_____________
Television
_____________
Car engine
_____________
Computer
_____________
Turbine
_____________
Motor
_____________
Transformer
_____________
Any
electrical device
_____________
What happens to wasted energy?
What happens to the wasted energy you get whenever
energy is changed from one form to another?
reated or d_______.
estroyed
Remember energy can not be c______
Wasted e_____
nergy spreads out (d_______)
issipated into the
s_________.
urroundings
This makes the energy harder to r____.
e-use
This is why it is important to r_____
educe the amount of
wasted energy there is.
Energy Transfer diagrams
22/05/2017
Consider a light bulb. Let’s say that the bulb runs on 100
watts (100 joules per second) and transfers 20 joules per
second into light and the rest into heat. Draw this as a
diagram:
“Input” energy
100 J/s
electrical
energy
“Output” energy
20 J/s
light energy
80 J/s heat
energy (given to
the surroundings)
Example questions
Consider a kettle:
2000 J/s
electrical
energy
Sound
energy
Wasted
heat
Heat to
water
1) Work out each energy value.
22/05/2017
Consider a computer:
150 J/s
electrical
energy
10 J/s
wasted
sound
20 J/s
wasted
heat
Useful
light and
sound
1) How much energy is converted
into useful energy?
22/05/2017
Here is a more complex energy transformation diagram,
the sort used by engineers.
This one is for an aeroplane engine.
Choose appropriate words to fill in the gaps below:
Energy is required to do ________.
work
joules (J)
Energy is measured in ________
Energy cannot be created or ___________
destroyed but can only
change ________.
form
Kinetic energy is the energy possessed by __________
moving bodies.
When an object is lifted up it gains gravitational
potential
_____________
energy.
Heat or __________
thermal energy is often produced as a _________
wasted
energy form, dissipated to the surroundings.
WORD SELECTION:
potential moving
joules thermal
work
wasted
form
destroyed
Do Now
How much
energy sort,
please arrange
the statements
in order of how
much energy is
involved .
•
•
•
•
•
•
•
•
•
•
•
•
•
Energy to drive a car 60 miles:
250,000,000 J
Energy stored in 1 litre of petrol:
34,000,000 J
Energy used by the human body for 1 day: 10,000,000 J
Energy in 1 unit on electricity bill (costs 15p): 3,600,000 J
Energy in a typical chocolate bar:
1,000,000 J
Energy to boil 1 l of water, from freezing:
500,000 J
Energy stored in a peanut:
25,000 J
Kinetic energy of a fast-moving cricket ball: 1000 J
Energy stored in one new AA battery:
1000 J
Energy from burning one whole match:
1000 J
Energy to lift up an apple by one metre:
1J
Energy to make the human heart beat once: ½ J
Energy to press key on computer keyboard: 1/100 J
Learning Today
• Potential Energy – Ep.
• Homework Potential Energy Sheet due
Thursday 12th January 2012
• Kinetic Energy – Ek
• If you need to find me, I will usually
be in my classroom SS15 or the
science office SS3
• Next lesson I want to spend half the
lesson building roller-coaster, you need
your log on details.
Potential Energy – Copy this
Gravitational potential energy is the energy an object
has because of its position in a gravitational field
GPE = mass x height x Change in height
E p  mgh
Ep= gravitational potential energy J
m = mass kg
g = gravitational field strength N/kg
h = height m
Ep
m g h
Now make mass, gravitational field strength
and height the subject of the formulae
Rearranging the formulae
E p  mgh
Ep
m g h
E p  mgh
Ep
Ep= gravitational potential energy (J)
m = mass (kg)
g = gravitational field strength (Nkg-1)
h = height (m)
m
Ep
gh
g
m g h
Ep
mh
h
Ep
mg
Example
Woof!
(help!)
A dog of mass 12 kg falls from an aeroplane
at a height of 3.4 km. How much
gravitational energy does the dog have as it
leaves the aeroplane?
On earth g = 10 m/s2
Mass of dog = 12 kg
Height = 3.4 km = 3400 m
Example
On earth g = 10 m/s2
Example
Mass of dog = 12 kg
GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J
Height = 3.4 km = 3400 m
Example
GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J
Just before the dog hits
the ground, what has this
GPE turned into?
Example
GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J
KE at bottom = 408 000 J
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Kinetic energy
Some example questions…
22/05/2017
How much gravitational potential energy have the following objects
gained?:
1. A brick that weighs 10N lifted to the top of a house
(10m),
2. A 10,000N car lifted by a ramp up to a height of 50cm,
3. A 70kg person lifted up 50m by a ski lift.
How much GPE have the following objects lost?:
1. A 2N football dropping out of the air after being kicked
up 30m,
2. A 0.5N egg falling 10m out of a bird nest,
3. A 10,000N car falling off its 50cm ramp.
4. Mr Richards when bungi-jumping off a 110-metre high
bridge in Zambia in August
Energy changes
Kinetic energy
This is the energy possessed by an object
due to its movement.
What factors will increase the amount of
kinetic energy a moving object has?
The shape of the object
The mass of the object
The height of the object

x

x
The velocity of the object
© Boardworks Ltd 2003
Kinetic Energy Copy this
1 2
Ek  mv
2
E
k
Ek = kinetic energy J
m = mass
kg
v = speed
m/s
½
m
v2
v
2Ek
m
m
2Ek
v2
Kinetic Energy
Now make mass and velocity
the subject of the equation
1 2
Ek  mv
2
Ek = kinetic energy J
m = mass
kg
v = speed
m/s
E
k
½
m
v2
v
2Ek
m
m
2Ek
v2
Mass and speed
If you increase the mass of a moving object you
increase the kinetic energy.
If you double the mass, you double the kinetic energy.
If you increase the speed of a moving object you
increase the kinetic energy.
BUT… If you double the speed, you quadruple the
kinetic energy.
This is why even if you are slightly above the speed
limit, you increase the kinetic energy of a moving car
a lot, this means it is harder to stop the car and there
is more chance of an accident.
© Boardworks Ltd 2003
Kinetic energy calculation
A car has a mass of 400kg and a velocity of 10 ms-1,
what is the kinetic energy of the car?
Kinetic energy
= ½ mass(velocity)2
= ½ x 400 x(10)2
= 20 000 J
© Boardworks Ltd 2003
Example
A bullet of mass 150 g is travelling at 400
m/s. How much kinetic energy does it have?
Example
A bullet of mass 150 g is travelling at 400
m/s. How much kinetic energy does it have?
Ek = mv2/2 = (0.15 x (400)2)/2 = 12 000 J
Using conservation of energy
• Now with a falling object as it falls faster
and faster the potential energy is gradually
converted to kinetic energy. At the moment
just before impact, potential energy is zero
and all the potential energy has been
converted to kinetic energy we can use this
to solve problems and find the velocity
1 2
mv  mgh
2
Now a bit of algebra
1 2
mv  mgh
2
Example
GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J
KE at bottom = 408 000 J
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J
KE at bottom = 408 000 J
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J
KE at bottom = 408 000 J = mv2/2
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
408 000 = mv2/2
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
408 000 = mv2/2
2 x 408 000 = 12 x v2
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
408 000 = mv2/2
2 x 408 000 = 12 x v2
816000 = 12v2
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
408 000 = mv2/2
2 x 408 000 = 12 x v2
816000 = 12v2
68000 = v2
Just before the dog hits the
ground, what has this GPE
turned into? Kinetic energy
Example
408 000 = mv2/2
2 x 408 000 = 12 x v2
816000 = 12v2
68000 = v2
261 = v
v = 261 m/s
Assuming no energy is lost as air resistance – in
reality the dog would have reached
TERMINAL VELOCITY
Let’s try some questions!
Stick them in first!
Homework
th
Due next Thursday 14 April
Finish ALL
questions on Kinetic
and Gravitational
energy
What type of energy is stored in a coiled spring?
A. Sound
B. Kinetic
C. Elastic

D. Gravitational
© Boardworks Ltd 2003
What type of energy is stored in baked beans?
A. Sound
B. Gravitational
C. Chemical

D. Elastic
© Boardworks Ltd 2003
What is the change in gravitational potential
energy of a weight of 60N that moves through
a distance of 6m?
A. 10J
B. 360J

C. 66J
D. 54J
© Boardworks Ltd 2003
What is the kinetic energy of a ball of mass 6kg
and velocity 5ms-1?
A. 75J

B. 30J
C. 1.2J
D. 150J
© Boardworks Ltd 2003
What type of energy is stored in coal, oil and
natural gas?
A. Light
B. Heat
C. Sound
D. Chemical

© Boardworks Ltd 2003
Don’t forget! Test!
• Use the revision sheet to help you study!
• Test on Wednesday 2nd February
Energy Circus
Around the room are a few examples of
energy changes (some simple, some a little
more complicated!)
For each example I want you to write the
name of the experiment and then the energy
flow diagram for that experiment
You will have 2 minutes on each example.
Ready?
Go!
Sankey Diagram
A Sankey diagram helps to show how much
light and heat energy is produced
Sankey Diagram
The thickness of each arrow is drawn to
scale to show the amount of energy
Sankey Diagram
Notice that the total amount of energy
before is equal to the total amount of energy
after (conservation of energy)
Efficiency
Although the total energy out is the same,
not all of it is useful.
Efficiency
Efficiency is defined as
Efficiency (%) = useful energy output x 100
total energy input
Efficiency
Efficiency is defined as
Efficiency (%) = useful energy output x 100
total energy input
Can you copy this (with title)
please?
Example
Efficiency = 75 x 100 = 15%
500
Energy efficient light bulb
Efficiency = 75 x 100 = 75%
100
Energy efficient light bulb
Efficiency = 75 x 100 = 75%
100
That’s much
better!
More complex examples
Let’s try some questions!
Stick the sheet into your books
and answer the questions