Download Energy Flow in Technological Systems

Energy Flow in Technological Systems
Steam Engines
- A boiler generates steam and a steam engine converts the
steam pressure into motion (mechanical energy).
- 1698 Savery in England received the first patent for a
steam engine to help remove water from mines (see p.
142)
- 1712 Newcomen invented a much improved steam
engine (p. 143)
- 1757 James Watt modified the design of the steam
engine so eventually it became useful in many industries
– Industrial Revolution.
- 1884 Charles Parsons perfected the steam-turbine engine
– no pistons (p.147).
- Steam-turbine engines still today power giant ocean
liners and cruise ships.
Scientific Theories of Heat
1. Phlogiston Theory
- Substances that could burn contained an invisible fluid –
phlogiston.
2. Caloric Theory
1
- Caloric or heat was a massless fluid that was found in all
substances
- Caloric could not be created nor destroyed but could
flow from one substance to another
- Caloric always flowed from warmer objects to cooler
objects
- J. Black defined a unit of caloric – the calorie.
- 1 calorie was defined as the quantity of caloric that
would increase the temperature of 1 g of water by 1ºC.
3. Modern Theories
- Count Rumford suggested that there is no substance
such as caloric, he believed that there was a relationship
between mechanical energy and heat
- Mayer a German doctor discovered that heat is related to
energy
- Joule a British physicist was given the credit for
discovering that mechanical energy is equivalent to heat.
- The SI unit for energy, the joule is named in his honour.
1 cal = 4.2 J
Energy
- Is defined as the ability to do work.
Work
- is the transfer of mechanical energy from one object to
another
2
- Is a push or pull on an object that results in motion in
the direction of the force applied.
F
d
W=Fd
F = ma
W = work in Joules (J)
F = force in Newtons (N)
d = distance in metres
m = mass in kg
a = acceleration in m/s2
F = force in Newtons (N)
Rearranged formulas for work:
d=W
F
F=W
d
1. A force of 30 N is used to lift an object to a height of 2.5 m.
Find the work done.
3
F = 30 N
d = 2.5 m
W=?
W = Fd = (30)(2.5)
W = 75 J
2. It takes 12 000 J of work to pull a crate a distance of 200 m.
Find the force applied.
W = 12 000 J
F=W
d = 200 m
d
F=?
= 12 000
200
F = 60 N
p. 154 #1-9
4
Using Graphs to Determine Work
F (N)
Area = l·w
d (m)
Area = lw = Fd = Work
Thus,
A = Fd = W
or
Area = Work
5
F (N)
d (m)
Work = Area = b·h
2
(1/2 a rectangle)
F (N)
d (m)
To find the total work done find the total area under the
graph. Break up the graph into shapes (rectangles and
triangles).
Find the area of each and then add them up.
6
F (N)
8
5
A1
A2
d (m)
10
25
A1 = (10)(5) = 25 J
2
A2 = (15)(8) = 60 J
2
AT = 85 J
Thus, W = 85 J
Law of Conservation of Energy
- Energy cannot be created or destroyed, but it can be
converted (changed) from one form to another
Calorie
- Today the calorie is defined as the amount of energy that
must be added to 1.0 g of water to increase its
temperature by 1.0 ºC
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Heat and Thermal Energy
- Kinetic energy – energy of motion
- The greater the kinetic energy of a substance the faster
the particles of the substance are moving around –
kinetic molecular theory
- Heat is now defined as the transfer of thermal energy
from one object to another
- Heat and work are mechanisms by which energy can be
transferred from one object to another
Specific Heat Capacity (c)
- Is the amount of heat required to raise the
temperature of 1.0 g of a substance by1ºC.
- is different for every substance
- symbol is ‘c’
- units are ‘ J/g ºC’
Temperature
- is a measure of the average kinetic energy of the
individual atoms or molecules in a substance
Thermodynamics
- is the field of physics that deals with forces and motion
involving heat (the transfer of thermal energy)
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-
-
-
1. First Law of Thermodynamics
Energy cannot be created or destroyed, but can be
transformed from one form to another or transferred
from one object to another
2. Second Law of Thermodynamics
It is not possible for any process to remove thermal
energy from an energy source and convert it entirely into
work
No process can be 100 % efficient.
Energy is lost as heat (friction)
Thermal energy always flows from the warmer object to
the cooler object
p. 157 #10
p. 163 #1 – 11
Complete sentences or copy the
question first.
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Internal Combustion Engines
- fuel is burnt inside a cylinder
- the hot gases expand and push the piston down the
cylinder
- modern engines have 4, 6, or 8 pistons all attached to the
same crankshaft
- these pistons are designed to fire at different times
- at least one piston is always in its’ power stroke
- examine diagram p. 165
- the internal combustion engines release greenhouse
gases and gases that contribute to smog and acid rain
10
Production of Electrical Energy
- all commercial electrical energy is
produced by electrical generators
- Electrical generators have huge magnets
with coils of wire turning between the
magnets.
- in most generators turbines turn the coils
- kinetic energy of the coils is converted
into electrical energy
- steam pressure drives the turbines for 1/3
of the electrical energy produced in
Canada
- the heat that boils the water comes from
the combustion of fossil fuels or nuclear
reactions
- hydro-electric generating stations produce
2/3 of the electrical energy
- the pressure of the water behind the dam
forces the turbines to turn
- a few places in Canada are able to make
use of wind energy to produce electrical
energy
Assignment: p. 172 (key terms)
p. 172 #4,6,10,12
p. 170 #1 - 3
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Measuring Motion
- Quantities that describe magnitude but not
direction are called scalar quantities
- Speed, distance and time are scalar
quantities (e.g. 100 km/h, 50 m, 2 s).
- Quantities that include direction as well as
magnitude are vector quantities
- Velocity, displacement and position are
vector quantities (e.g. 100 km/h South,
50 m West)
Distance vs Displacement
- Distance is measured along the actual
path travelled
- Displacement is measured along a
straight line joining the initial and final
positions
- Adding vectors head to tail allows you to
calculate displacement in two dimensions
- Adding vectors along a straight line allows
for calculating displacement in one
dimension (directions N, S, E, W or +/-)
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15 m
7m
Distance = 15 + 7 = 22 m
Displacement = 15 +(-7) = 8 m
Speed of an object
- Speed is the total distance traveled
divided by the total time.
v=d
t
v = speed in m/s, km/h
d = distance in m, km,
t = time in s, h,
13
Rearranged formulas:
d = vt
t=d
v
Converting km/h to m/s divide by 3.6
m/s to km/h multiply by 3.6
e.g.
100 km = ___?__ m/s
h
100 x 1,000 m ÷1000 = 100 = 27.8 m/s
3,600 s ÷ 1000
3.6
e.g. A car travelled a distance of 280 km in 4.0 h. What was
the speed of the car in km/h and m/s?
d = 280 km
v=d
t = 4.0 h
t
v=?
v = 280 = 70 km/h = 19.4 m/s
4
Assignment:
p. 171 (i-m)
Activity Pg 178 (procedure 1&2)
Practice Problems p. 184 – 185 #10 – 22
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Uniform Motion
- During uniform motion velocity is constant.
- On a distance-time graph the line is a straight line
(horizontal or slanted)
- On a d-t graph the time is always on the horizontal (x)
axis
- Slope = rise
Run
Slope = velocity
- **When a distance (position) vs time graph is a slanted
straight line the velocity is constant.
d(m)
rise
run
t(s)
15
slope = Rise = d = velocity (speed)
Run
t
d (m)
10
rise
run
t (s)
5
To find slope use the following steps:
Step 1 – Pick any two points on the graph
(the points must be exactly on the line).
Step 2 – From these two points draw two lines, one
parallel to the x-axis and the other parallel
to the y-axis, until they form a
right triangle.
Step 3 – Divide the rise (d) by the run (t) to get the
slope.
Slope = ∆d = 10 m = 2 m/s
∆t
5s
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Acceleration







Acceleration is a change in velocity during a time
interval (speeding up or slowing down)
is a vector quantity
a force is required to change motion in some way
units for acceleration are m/s2 or m/s/s
5 m/s2 means the speed is changing (increasing) by
5 m/s every second
Acceleration can be negative (object is losing
speed) e.g. –2 m/s2 means the speed is decreasing
by 2 m/s every second.
negative acceleration is also known as
deceleration.
Formula is: a = ∆v
t
∆v = vf - vi
∆v = change in speed in m/s
t = time in seconds
a = acceleration (m/s2)
vf = final speed (m/s)
vi = initial speed (m/s)
Acceleration formula is usually written as:
a = vf - vi
t
17
at = vf - vi
Note: when solving acceleration problems speed (v) must be
in m/s and time must be in seconds.

Rearranged formulas:
t = vf - vi
a
vf = vi + at
vi = vf – at
1. What is the acceleration of a car if its speed is increased
uniformly from 40 m/s to 70 m/s in 3 s?
vi = 40 m/s
vf = 70 m/s
a = vf - v i
t=3s
t
a=?
= 70 - 40
3
a = 10 m/s2
2. What is the acceleration of a car if its speed is decreased
uniformly from 80 m/s to 50 m/s in 10 s?
18
vi = 80 m/s
vf = 50 m/s
t = 10 s
a=?
a = vf - v i
t
= 50 - 80
10
a = - 3 m/s2
3. How much time would it take for an object, which
starts from rest and accelerates at 10 m/s2, to reach a
velocity of 40 km/h?
vi = 0
a = 10 m/s2
vf = 40 km/h = 11.1m/s
t=?
t = v f – vi
a
= 11.1 – 0
10
t = 1.1 s
4. An airplane flying at 80 m/s is accelerated uniformly at
the rate of 1.5 m/s2 for 15 s. What is its final speed?
vi = 80 m/s
a = 1.5 m/s2
t = 15 s
vf = ?
vf = vi + at
vf = 80 + (1.5)(15)
vf = 102.5 m/s
Assignment:
p. 192 # 23 – 31
19
Graphing Uniformly Accelerated Motion
(Speed-time graph)
The slope of a speed-time graph is equal to the acceleration.
Time is always on the horizontal.
20
Kinetic Energy (KE or Ek)
- KE is the energy of motion
- the amount of KE an object has depends upon its
speed and its mass
Formula:
Ek = ½ mv2
KE = mv2
2
or
Ek = kinetic energy in joules (J)
m = mass of the object in kilograms (kg)
v = speed in metres per second (m/s)
1 J = 1 kg · m2
s2
Rearranged formulas:
m = 2KE
v2
v=
2KE
m
1. A car with a mass of 2,200 kg is moving at a speed of 16
m/s. What is the kinetic energy of the car?
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m = 2,200 kg
v = 16 m/s
KE = ?
KE = mv2
2
KE = (2200) (16)2
2
KE = 281,600 J = 2.8 x 105 J
2. A hockey puck has a mass of 220 g. If the hockey puck
has 67 J of kinetic energy, what is its speed?
m = 220 g = 0.220 kg
KE = 67 J
v=
2KE
v=?
m
v = 24.7 m/s
Pg 199 Questions #32 – 40
Pg 204 Questions #1-5
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Potential Energy (PE)
-
PE is stored energy
it has the potential to do work
many forms of PE
e.g. elastic, chemical, nuclear, electrical and
gravitational.
Gravitational Potential Energy (PE)
- is the energy an object has due to its position above the
earth’s surface or some other point of reference (a
table)
- for an object to posses PEg, work must be done on it
- Thus ‘work and energy’ are equivalent
Formula,
PE = mgh
m = mass in kg
g = 9.81 m/s2
h = height in m
PE = potential energy (J)
PE = mgh
h = PE
mg
m = PE
gh
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***Weight is the force of gravity on an object – it does
change with location.
Fg = W = mg

W = weight in N
units for weight are Newtons (1 N = kg m/s2)
***Mass is the amount of material in an object – it
does not change with location.

Base unit for mass is the kg.
What is the weight of an 80 kg person?
W = mg = (80)(9.81) = 785 N
1. A 20 kg objects sits 15 m above the ground. What is
its potential energy with respect to the ground?
m = 20 kg
PE = mgh
h = 15 m
= (20)(9.81)(15)
PE = ?
PE = 2,943 J
2. How far would you have to lift a 2.5 kg brick to give
it 50 J of gravitational potential energy?
m = 2.5 kg
PE = 50 J
h=?
h = PE =
50
mg (2.5x9.81)
h=2m
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p. 212 # 41- 49
p. 216 # 1- 6
p. 217 - (a, b, d, e, i, m, n, o)
p. 218 – key terms
p. 219 #21, 23 - 26
25
Main formulas:
d = vt
a = vf - vi
t
W=Fd
F = ma
Weight = Fg = mg
g = 9.81 m/s2
Ek = ½ mv2
Ep = mgh
Graphs
26
d
d vs t
Slope = speed
t
F
F vs d
Area = work
d
Assignment:
27
Define:
1.Vector
2. Scalar
3. Displacement
4. Distance
5. Thermodynamics
6. First Law of Thermodynamics
7. Second Law of Thermodynamics
8. Calorie
9. Steam engine
10. Temperature
11. Acceleration
12. Gravity
13. Potential energy
14. Uniform motion
15. Kinetic energy
16. How did Newcomen’s engine work
17. Work
18. How did Savery’s engine work
Read ch. 4 & 5
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Efficiency of Energy Conversions
Efficiency is a measurement of how effectively a
machine converts energy input into useful energy
output
- The energy that perform the task is called useful
energy
- Some energy is always lost – usually as heat
Efficiency = useful output energy
total input energy
- Second Law of Thermodynamics
“No process can be 100 percent efficient.”(some energy
is always wasted)
Eff. = Eout
Ein
E = Energy
Formula can be rearranged for:
Ein = Eout
Eff.
and
Eout = (Eff)(Ein)
29
Efficiency is usually given in percentage – so we
multiply the answer by 100.
Eff. = Eout x 100
Ein
Or
Eff. = Wout x 100
Win
W = Work
Note: Energy = Work
1. A crane lifts a load and in the process it does 2.30 x
104 J of work. If the potential energy of the load at the
maximum height is 8.00 x 103J, what is the efficiency
of the crane?
Win = 2.30 x 104 J
Wout = 8.00 x 103 J
Eff. = Wout x 100
Eff. = ?
Win
Eff. = 8.00 x 103 x 100
(2.30 x 104)
Eff. = 35%
30
2. In heating a pot of water 2 x 103 J of heat was
supplied by the stove. If only 5 x 102 J of heat was
actually gained by the water, what was the efficiency of
the stove?
Ein = 2 x 103 J
Eout = 5 x 102 J
Eff. = Eout x 100
Eff. = ?
Ein
Eff. = 5 x 102 x 100
2 x 103
Eff. = 25%
3. An internal combustion engine with an efficiency of
15% is used to do 3.20 x 104 J of useful work. Calculate
the energy input that had to be supplied by the
combustion of fuel in the engine.
Eff. = 15% = 0.15
Eff. = Eout
Eout = 3.20 x 104 J
Ein
Ein = ?
Thus,
Ein = Eout
Eff.
0.15 = 3.20 x 104
E
0.15E = 3.20 x 104
0.15
0.15
31
Ein = 3.20 x 104
0.15
Ein = 2.13 x 105 J
Assignment:
p. 227 #1-3 p. 244 #1-9
32
Energy Efficiency and the Environment
- Every time there is an energy conversion some energy
is wasted in the form of heat
- Example – hydro-electric generating stations are 70%
efficient while coal burning stations are 35% efficient
- Businesses and industry are the largest consumers of
energy and so it is important that they use energy
efficiently
- Many companies have already installed more energy
efficient lighting, heating and cooling equipment to
conserve energy
- Another less obvious method is to encourage
industries to use cogeneration.
- Cogeneration is the process of using waste energy
from one process to power a second process
- E.g. In a thermal power station, the steam that is used
to turn the turbines could then be used to heat local
buildings
- All sectors of society must become conscious of the
problems and search for solutions
- the solutions must be sustainable
- a sustainable process will not compromise the
survival of living things or future generations while
still providing for our current needs
33
Assignment: p. 218 – key terms
p. 242 #1-3, 6
p. 243 - a, b, d, e, g, j
p.244 – key terms
p.245 #18-24
p. 252 #44 – 56
p. 250 #4, 19 - 35
34