Comeniusproject
TEWISE
„THERMODYNAMICS”
Wszyscy lubimy ciepło…
Józefina Turło
Andrzej Karbowski
Grzegorz Osiński
Krzysztof Służewski
EXPRESSTRAIN
Instytut Fizyki
Uniwersytet Mikołaja Kopernika, Toruń, Polska
2003-2005
COMENIUS-C2110650-CP-1-2002-AT
All rights reserved.
Privacy [email protected] for the project -team:
by Project "TEWISE" Copyright © 2002-2010
This project has been funded with support from the European Commission.
This publication [communication] reflects the views only of the author, and the Commission
cannot be held responsible for any use which may be made of the information contained therein.
THERMODYNAMICS
List of modules 1- 4
I. HEAT AND TEMPERATURE
1.
Examples from nature – hot and cold
2.
Concept of heat
3.
Concept of temperature
4.
Measurements of temperature
4.1. Temperature scales – Kelvin, Celsius and Fahrenheit
4.2. Measurements of cold and warm water temperature
II. WAYS OF ENERGY TRANSFER BY HEAT
1.
Conductors and insulators
1.1. Questions identifying preconceptions
1.2. Experiment concerned with heating of wood and copper
1.3. Thermal properties of different materials
2.
Convection
2.1. Convection in glass pipe
2.2. Convection of hot and cold air in the room
3.
Radiation
4.
Model explanation
III. THERMAL EXPANSION
1. Examples from everyday life
2. Experiment with metal expansion
3. Dependence on temperature – mathematical description
IV. STATES OF MATTER
1. Gases, liquids, solid states structure
1.1. Examples from nature
1.2. Model of states of matter
2. Change of states
3. General scheme of states of matter changes
HEAT AND TEMPERATURE
ÿ
ÿ
ÿ
What does it mean “cold”?
Why you fell that glass with tea is hot?
Why the snow is cold?
1. Examples from nature – hot and cold
Let’s make a simple experiment
HOT
WARM
ICE
HOT
WARM
ICE
First put your left hand to the water with ice and right to the hot water, wait a
half a minute, then put two hands together to a warm water. What are you
feeling now? Do you know why?
2. Concept of heat
Heat is a process of energy transfer between bodies of different temperature.
HOT BODY
COLD BODY
transfer of energy by heat
Energy transfer is taking place during the collision of body molecules
Examples:
ÿ Transfer of energy by heat from oven to air in the room and from air to all
elements in the room.
ÿ Transfer of energy by heat from the gas burner to the kettle and next to
the water inside the kettle.
ÿ Can you give more examples?
TEWISE
„Heat and temperature”
1a
3. Concept of temperature
Let’s see how molecules are moving and make collisions between themselves on
the 2 dimensional air table (use the video movie).
Let’s see now the simulation of molecules motion in 3 dimensional model (use
the video movie)
Particles are moving in the box, all in the random directions. They transfer
energy during collisions between themselves and between them and the walls.
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„Heat and temperature”
1b
Temperature depends on particles speed:
T ~ particles speed
If temperature increases, the speed of molecules increases too, if temperature
decreases the speed decreases too.
As the result we can define the temperature:
Temperature is a physical quantity characterising the kinetic energy of linear
motion of molecules.
4. Measurements of temperature
4.1. Temperature scales – Kelvin, Celsius and Fahrenheit
The first mercury thermometer was constructed by Gabriel Fahrenheit in
Gdansk in 1720. Zero point was connected with the lowest winter air
temperature – (approximately -17 oC) and 100 oF was connected to the body
temperature of Fahrenheit’s wife.
For Kelvin scale 0 is absolute value which presents the lowest temperature in
nature – then particles are not moving – are at rest. 273 K is a temperature of the
freezing water.
The Celsius scale, most popular in Europe, is connected to the freezing (0 oC )
and boiling (100 oC) points of water. Let’s see comparison of these three scales
in the table below:
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„Heat and temperature”
1c
The formula for units conversion is as follows:
4.2. Measurements of cold and warm water temperature
Let’s prepare two glasses – first one with warm water and the second one with
the ice. Please measure the temperature using ordinary thermometers and
electronic temperature detector.
Ordinary thermometers
Electronic measurement
Temperature of the frozen water is 0 oC and of warm water 22 oC.
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„Heat and temperature”
1d
WAYS OF ENERGY TRANSFER BY HEAT
1. Conductors and insulators
• Why the teaspoon in the hot cup of tea is hot?
• How the air in the room is hot when warm oven is there?
1.1. We can recognize three main different ways of thermal energy transfer
(by heat): conduction, convection, radiation.
1.2. Experiment concerned with heating of wood and copper
Please prepare the candle, two pieces of paper and wood and metal cylinders.
Make experiment (or see the video film) and answer the question: which
cylinder is heat conductor and which is heat isolator?
After the process of heating the paper with wood cylinder is more dark than the
paper with copper cylinder. It means that metal is a good heat CONDUCTOR
but wood is an ISOLATOR
1.3. Thermal properties of different materials
The figure below shows an experiment presenting the thermal properties of
different materials. There is a series of rods made from different materials and
covered by wax. Their ends are placed in hot water. What we observe?
We can notice that wax is melting first on the copper and aluminium rods and
lastly on plastic and glass rods. The reason is – some materials are good heat
conductors but some good heat isolators.
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„Ways of energy transfer by heat”
2a
The table below presents heat properties of some materials.
the best conductor
the worst conductor
diamond
silver, copper
aluminium, steel, lead
ice, marble, glass
polyethylene, nylon
rubber, wood
polystyrene
glass wool
the worst insulator
the best insulator
2. Convection
2.1. Convection in glass pipe
Please heat the water in the closed glass pipe and observe the behaviour of cork
pieces in water (make experiment or see the video film).
We can see that when one part of fluid or gas is hotter than another part, the hot
part tends to move upwards. We are dealing with the convection process.
Convection is a process of thermal energy transfer (by heat). As the result
convection currents circulate around the fluid or gas.
2.2. Convection of hot and cold air in the room
There is the scheme of air circulation in the room as a result of convection
currents.
Window
TV set
Radiator
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„Ways of energy transfer by heat”
2b
3. Radiation
The process of radiation transfers thermal energy in the form of heat even there
is no connection between source of heat and the receiver. For example, heat
energy from the Sun reaches us as radiation, because it is transported through
open space.
Please notice that there is no connection between cup and books shown in the
picture below, but after a while cold books will be hotter.
Heat energy will be transferred between hot cup to cold books by radiation
which we called infra-red radiation. We can not see it, but we can feel it on our
skin because it raises its temperature.
Thermal camera* can make the picture of infrared radiation
of different bodies as for example human body (see picture
on the left side). In this picture the red and bright places
indicate hot parts of human body, but dark places- cold
parts. Please notice that the hottest place of human body is
the head.
This camera can be also used during the night. When your
eyes didn’t see anything camera detect all radiating objects,
as for example: peoples, animals and machines.
The name of this special camera is noctovisor.
* Extended content
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„Ways of energy transfer by heat”
2c
4. Model explanation*
The energy transfer by heat is going always from hot to cold materials
HOT
COLD
energy transfer by heat
ÿ The molecules with higher energy (higher velocity and mass) transfer
it to the molecules with the lower energy.
ÿ This process is taking place in a gases, liquids and solids.
ÿ In a gases and liquids transfer of energy occurring during collisions.
ÿ In solids vibrating atoms in one part of material pass on their
vibrations to atoms close to them.
* Extended content
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„Ways of energy transfer by heat”
2d
THERMAL EXPANSION
1. Examples from everyday life
Let’s see how bridge is constructed. It contains expansion joints (see picture
below). Why? What’s going on with metals when they are hot or cold?
The bridges must be constructed with the use of expansion joints to allow the
thermal expansion, otherwise they might buckle.
Please observe the construction of railroads (picture below).
There are expansion joints
in the railroads
What we see at the electrical traction wires?
The electric wires are hanging down here, because it was a sunny day when the
photo was taken. But during the winter time temperature is falling down and the
wires start contract. They use the “extra piece of sunny wire”, so they will not
brake off.
When is hot metals are expanding. When is cold - they contracting.
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„Thermal expansion”
3a
2. Experiment with metal expansion
Let’s see experiment presenting expansion of metal piece in a special device
(make experiments or see the video film).
When we heat the device the metal arm is expanding. We correct its length by
using screw. When we stop heating we put a cold piece of fabric on a metal arm
and observe that metal arm starts contracting – as it broke piece of glass.
3. Dependence on temperature – mathematical description
Let’s tray to calculate how big expansion is when we heat a piece of metal.
a) The starting situation is as follows. The piece of metal have length L1 and
temperature T1:
T1
The piece of metal (cold)
L1
∆
The piece of metal (hot)
T2
L2
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„Thermal expansion”
3b
b) When we heat the piece of metal, temperature increases and the metal
expands.
The new length is L2 at temperature T2.
The change of temperature: ÿT = T2 – T1
The change of length: ÿL = L2 – L1
For temperature change
change L, is:
T the mathematical formula describing the length
L= L T
where is linear coefficient of thermal expansion. It is different for different
materials. Some examples of linear coefficient are collected in a table below:
Solids
Copper
Aluminium
Gold
Steel
[1/oC]
1.7 *10-5
2.4 *10-5
1.4 *10-5
1.2 *10-5
Calculation exercise
Find the change in the total length of the 2700 m long Golden Gate Bridge, as
the temperature increased from 5 OC in the morning to 25 OC at the noon. The
bridge is constructed with steel.
Solution
In the table we can find that steel have a coefficient of thermal expansion –
1.2*10-5 1/OC.
Let’s apply equation:
ÿL =
L ÿT
ÿT = 25 C – 5 C = 20 C
then
ÿL = L ÿT = 1,2 *10-5 1/OC * 2700 m * 20 OC = 0,65 m = 65 cm
O
O
O
That’s a reason that expansion joints are very necessary!
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„Thermal expansion”
3c
STATES OF MATTER
1. Gases, liquids and solid states
1.1. Examples from nature
a.
What does it mean states of matter?
b.
What kind of matter do you see in the pictures below?
You can recognize three different state of matter:
• gas – vapour of the water in the kettle,
• liquid – tap water,
• solid state – icicle behind the window.
1.2. Model of states of matter
Here you see how molecules are packed in different states (solid state, liquid and
gas).
Solid state
Liquid
Gas
In the solid states molecules are packed very tightly. In liquids molecules have
some space between themselves. And in gases molecules are moving freely.
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„States of matter”
4a
2. Change of states
All substances can change their states and it depends on temperature.
Let’s see the pictures below showing the model of changing state of gas:
In picture a the temperature is rather high, so atoms moving quickly and make
collisions between themselves.
In picture b and c we start decreasing temperature and atoms start moving more
slowly and during the collisions they stick together, first to small groups and
later to the bigger clusters.
In picture d we can see that all molecules are grouped. There is very low
temperature and gas is changing state to the liquid.
The process when gas turns into liquid is called condensation.
3. General scheme of states of matter changes
For 3 states of matter there are 6 possible ways of their change. All of them are
described in the below scheme:
resublimation
condensing
GAS
evaporation
freezing
LIQUID
melting
SOLID
sublimation
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„States of matter”
4b
Expresstrain
Heat and Work
What you do with your hands during the winter time,
when there are freezing?
Let’s remind experiment from the previous module – 4b “States of matter“ – concerning the
process of heating a piece of ice which turned first into water and then into steam.
The energy we have put into the ice does two things:
• it increases the kinetic energy of the particles – they move faster, the
temperature rises,
• it increases the potential energy of the particles – bonds are breaking and the
substance changes state.
See picture below, showing compression of air in a bicycle pump:
As the plunger of the pump moves
downwards, it pushes the molecules
of the air and they move faster – their
kinetic energy increases and the
internal energy of the gas increases.
Gas becomes hotter.
Thus, we can compress an object to make it hotter. This process is very easy to perform with a
gas, because a gas can be easily compressed. We can use a force to do work on the gas and
hence to transfer energy to it.
We can express a work for compressing as:
W = Fx ,
where F is our force and x is displacement of pumps plunger.
Let’s introduce the concept of internal energy.
The internal energy U of an object is the sum of the kinetic energy and potential energy
of the random motion of all particles in the substance.
The change of internal energy is ∆U.
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„Heat and work“
5a
Expresstrain
The First Law of Thermodynamics
How a work can be transferred into heat?
Historical Joule’s experiment
In 1850 James Prescott Joule (1818-1889) made an
experiment which indicated that a heat is a form of energy
the same type as work.
He measured equivalent of mechanical energy to heat
energy: how many joules are equivalent to one calorie?
In the picture on the left you can see a draft of original
Joule`s experiment. Two weights, hanging on a line rotate a
shovels, which mix a water.
During this process the water heat up.
Using this experiment Joule demonstrated that work is equal
to heat energy.
The First Law of Thermodynamics
The increase in internal energy of a system is the sum of the work done on the system
and the energy supplied thermally to the system.
We can express this law mathematically:
∆ U = ∆Q − ∆W
where:
∆U – a change of internal energy,
∆Q – a change of energy supplied thermally to the system (so called “heat energy”),
∆W – a change of work done by the system.
Remark: Please notice that we are considering here the work done by the system, so we used
“–” sign in the equation. When the work is done on the system, we have to use sign “+” in
the above equation.
We can transfer this equation into:
∆Q = ∆U + ∆ W
Conclusions:
• When the work is done on the system, according to the first law of thermodynamics,
the internal energy of a gas increases and/or heat is transferred from the system.
• Summarizing, in any case, the first law says that we can’t get more out of a system
than we put in and/or than is already there. This have to be in agreement with the
energy conservation principle.
kgm 2
The units of work in legal system SI is joule [J] 1J = 1N × 1m = 2
s
The historical unit of heat is calorie [cal] – the amount of thermal energy,
which is required to change the temperature of 1gram of water by 1oC.
The mechanical equivalent of heat is: J = W/Q; 1 cal = 4,186 J.
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„ First Law of Thermodynamics“
6a
Expresstrain
Experimental verification of First Law of Thermodynamics
Let’s perform the experiment with the use of handy thermoergometer for evaluation of the
mechanical equivalent of heat.
Thermoergometer is shown in the picture below.
To make experiment we have to rotate the crank for
example 100 times trying to use the same value of
force, which is measured by the forcemeter.
When we are rotating the crank the sleeve and shackle
are grinding themselves inducing the friction force and
heating the defined mass of petroleum filling inside
the calorimetric dish.
After 100 rotations we measure the change of
temperature of the liquid.
The obtained data taken from the real experiment are
placed in the table below.
We use the equation:
ÿU = ÿQ + ÿW
when ÿU = 0 then ÿW = – ÿQ and |ÿW/ ÿQ| = 1
First, we calculate the work W done on the system:
W = F l 2 n = 1N 0,5m 2 100 = 314 J
where: F – friction force, l – length of arm; n – number of rotations.
Next we calculate the thermal energy (heat) created by the system:
Q = [m1cc + (m2 + m3)cg + m4cp] (t2 – t1) = 258,92 J
where: m1 – mass of calorimetric dish, (m2 + m3) – mass of grinding kit, m4 – mass of
petroleum, cc – specific heat of calorimeter, cg – specific heat of grinding kit, cp – specific heat
of petroleum, t1 – initial temperature, t2 – final temperature.
mass of calorimetric dish: m1 = 0.0072 kg initial temperature: t1 = 22 oC
mass of grinding kit: m2 + m3 = 0,05 kg
final temperature: t2 = 28 oC
mass of petroleum: m4 = 0,01737 kg
specific heat of calorimeter: cc = 452 J/(oC kg)
length of arm: 0,425 m
specific heat of grinding kit: cg = 500 J/(oC kg)
specific heat of petroleum: cp = 2100 J/(oC kg)
number of rotations: n = 100
force: F = 1 N
Using the above data we will get: W/Q = 314/258,92 1,21.
Thus, we see that work done on the system is equivallent to the thermal energy (heat) created
by the system (within the experimental error, which is rather high – about 20% in our case).
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„ First Law of Thermodynamics“
6b
Expresstrain
Why the car near the place of engine is hot after the journey?
Why some big engine, especially that in a big truck, needs
a cold water for safe work?
Heat engines
• A heat engine is a device that converts thermal energy to work.
• Many types of heat engines are available: gasoline engines in lawn mowers, diesel
engine in trucks and steam turbines used in electrical generators.
• All of them operate according to the same principle of transferring thermal energy to a
fluid, that uses some of that energy for the mechanical work.
The conservation of energy role requires for the engine that:
Thermal energy in = work + thermal energy out
or
Work = thermal energy in – thermal energy out.
Heat engine diagram description
In general, a heat engine takes heat from hightemperature reservoir (i.e. from a burning fuel) with
temperature Thot, converts some of it to useful work
output and rejects the remainder to low-temperature
reservoir (i.e. to cooler) with temperature Tcold (see
picture on the left).
Historical Heron’s engine
In figure on the left a model of a device know as Heron’s engine is
shown. This was invented around 150 B.C. by Heron in Alexandria,
Egypt. The flask is suspended by a cord so it is free to rotate. When
the water in the flask is boiling, steam go out through two pipes
(oriented in opposite directions), the flask rotates and does work.
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„ First Law of Thermodynamics“
6c
Expresstrain
What kind of energy resources is more ecological: coal or sun?
Please explain your choice.
Sources of energy
Non-renewable
Renewable
Wind energy: Giant wind turbines grouped
in wind farm turn electrical generators.
Solar energy: Mirrors and panels are used to
Fossil fuels: coal, oil and natural gas.
capture the Sun’s radiation energy.
Tidal and hydroelectric energy: The
gravitation pull of Moon and Sun causes
Ecological problems!
“bulges” of sea water on the Earth surface.
Burning fossil fuels in power stations and in As the Earth rotates, each part passes in and
cars pollute the atmosphere with harmful out of the bulge – the tide rises and falls.
gases. Acid rain is caused by sulfur dioxide Geothermal energy: Water is heated by the
and carbon dioxide emission.
hot rocks which lie many miles beneath the
Earth’s surface.
Biomass: Fast-growing plants or biomass
Nuclear fuels: uranium.
used to make hydrocarbons can be used as a
fuel.
The long-life waste radioactive materials can
cause a problem for the environment.
This kind of energy is non-polluting cannot
be exhausted.
World use of energy resources
Oil
Coal
40%
28%
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Gas
23%
Nuclear
7%
Hydroelectric
2%
Module „Sources of energy“
7a
Expresstrain
As we know from the previous unit over 90% energy used by us origins from
non-renewable resources.
How to save this energy in our everyday life?
Home insulation
Hot objects have a reservoir of internal energy. As we have seen in the previous modules,
energy tends to escape from hot objects, spreading to its cooler surrounding by conduction,
convection or radiation. To avoid quick energy spreading is the biggest problem if we wish to
save energy. To reduce lost of energy at home construction we have to use a special energythrift technology (see table and picture below):
Technology
Thick curtains, draught excluders
Loft and under floor insulating materials
Double and triple glazing of windows
Cavity walls
Foam or mineral wool in wall cavities
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How it works?
Cold air is prevented from entering and warm
air from leaving.
Conduction of heat through floors and
ceilings is prevented.
Vacuum between glass panels cuts out losses
by conduction and convection.
Heat losses by conduction through the walls
are prevented.
Heat losses by convection in the cavities are
reduced.
„Sources of energy“
7b
Expresstrain
SUMMARY AND TEST
SUMMARY:
1. Heat is a process of energy transfer between bodies of different temperature. It is
connected with thermal energy transfer during collisions of body molecules.
2. Temperature is a physical quantity characterising the kinetic energy of linear
motion of molecules.
3. Temperature scales:
a) Kelvin – absolute temperature scale based on absolute zero, when kinetic
energy of molecules is zero. The ice and steam points of water are 272 K and
372 K, respectively.
b) Celsius – the scale connected to 0 oC and 100 oC, freezing and boiling points of
water, respectively.
c) Fahrenheit – the scale with designation of 32 oF and 212 oF respectively, for
ice and steam points of water.
4. Conduction – Thermal energy (“heat”) transfer due to the molecular interaction
with no net mass movement. Occurs mainly in solids.
5. Convection – Thermal energy (“heat”) transfer by mass movement. Occurs in
liquids and gases with movement of all or parts of the fluid.
6. Radiation – Thermal energy (“heat”) transfer by means of infrared radiation.
7. Thermal expansion – when temperature of metals increases all metals expand,
when the temperature decreases, they contracts. Mathematical formula describing
this process is the following: ∆L = α L ∆T.
8. Change of phase - the transition from one phase of matter to another one, for
example, from solid to liquid, from liquid to gas.
9. Internal energy U - the energy of an object which is the sum of the kinetic
energy and potential energy of the random motion of all particles in the substance.
10. First law of thermodynamics - the increase in internal energy of a system is the
sum of the work done on the system and the energy supplied thermally to the
system. It express the conservation of energy principle applied to the
thermodynamics system: ∆ U = ∆ Q − ∆ W
11. Heat engine – A device that converts heat energy to work.
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„Summary and test“
8a
Expresstrain
TEST QUESTIONS
1. Temperature is: a) a measure of heat;
b) an everyday measure of hotness and coldness;
c) function of kinetic energy of linear motion of molecules;
d) both b) and c)
2. Could the temperature given in the weather report be the same expressed by the
Celsius and Fahrenheit scales?
3. When you leave an outside door open in a cold day, does “the cold come in” or
“the heat go out”?
4. Most substances expand with increasing temperature. Explain this expansion in
terms of kinetic-molecular theory.
5. When you eat a hot piece of apple pie, you may find that the crust is only
slightly warm, but the apple filling burns your mouth. Why?
6. Why is water used to store heat energy in solar homes?
7. Why a material is a good thermal insulator? Explain this with the use of
kinetic-molecular theory of matter.
8. Why do underground water pipes sometimes freeze only after it has been very
cold for several days?
9. When your skin is hot the blood vessels in the skin dilate or get larger in the
diameter. When the skin is cold, the blood vessels contract. What is the
purpose of this behavior?
10. Why do some liquids evaporate more readily than others?
11. People traveling in a hot region sometimes carry water in a porous canvas bag
that stays wet. They hang it on the front bumper of a car or truck. What is
purpose of this?
12. According to the first law of thermodynamics if heat is delivered to a system, it
transfers into:
a) temperature
b) work
c) internal energy
d) work and/or internal energy
13. The Earth has been warmed by the radiation from the Sun from millions of
years yet we think its average temperature has remained fairly steady. Why?
14. A thermos flask has a silver layer on its thin glass walls to reduce loss of heat
by:
a) convection
b) evaporation
c) conduction
d) radiation
15. Give some advantages and some disadvantages of using non-renewable fuels.
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„Summary and test“
8b