MODULE THERMODYNAMICS 1-4

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MODULE THERMODYNAMICS1-4
Grzegorz Osinski Józefina Turlo Andrzej Karbowski
Institute of Physics Nicolas Copernicus University, Torun, Poland Institute of Physics Nicolas Copernicus University, Torun, Poland Institute of Physics Nicolas Copernicus University, Torun, Poland
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I. HEAT AND TEMPERATURE Examples from nature
hot and cold Concept of heat Concept of
temperature Measurements of temperature II.
WAYS OF ENERGY TRANSFER BY HEAT Conductors and
insulators Convection Radiation Model
explanation III. THERMAL EXPANSION Examples from
everyday life Experiment with metal
expansion Dependence on temperature
mathematical description IV. STATES OF
MATTER Gases, liquids, solid states
structure Change of states General scheme of
states of matter changes
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HEAT AND TEMPERATURE
1. Examples from nature hot and cold
What does it mean cold? Why you fell that glass
with tea is hot? Why the snow is cold?
Lets make a simple experiment
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?
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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
• Transfer of energy by heat from oven to air in
  the room and from air to all elements in the
  room.
• Transfer of energy by heat from the gas burner to
  the kettle and next to the water inside the
  kettle.
• Can you give more examples?

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3.Concept of temperature
Lets see how molecules are moving and make
collisions between themselves on the 2
dimensional air table (use the video movie).
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Lets 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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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.

• 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 C) and 100 F was connected to
• the body temperature of Fahrenheits 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 C ) and boiling
  (100 C) points of water.

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The formula for units conversion is as follows
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Temperature conversion Java Applet
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Measurements of cold and warm water
temperature Lets 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.
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2. WAYS OF ENERGY TRANSFER BY HEAT
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?
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. We can recognize three main different ways of
thermal energy transfer (by heat) conduction,
convection, radiation. 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?
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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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• 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.
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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.
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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.
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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 didnt 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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4. Model explanation
The energy transfer by heat is going always from
hot to cold materials
HOT
COLD

• The molecules with higher energy (higher velocity
  and mass)
• transfer it to the molecules with the lower
  energy.
• This process is taking place in a gases, liquids
  and solids.
• In a gases and liquids transfer of energy
  occurring during collisions.
• In solids vibrating atoms in one part of material
  pass
• on their vibrations to atoms close to them.

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THERMAL EXPANSION

1. Examples from everyday life

Lets see how bridge is constructed. It contains
expansion joints (see picture below). Why?
Whats 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.
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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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Experiment with metal expansion
Lets 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.
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Dependence on temperature mathematical
description Lets tray to calculate how big
expansion is when we heat a piece of metal.

• The starting situation is as follows.
• The piece of metal have length L1 and
  temperature T1

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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 ?T T2 T1 The change of length
?L L2 L1 For temperature change ?T the
mathematical formula describing the length change
?L, is ?L a L ?T where a ?is linear
coefficient of thermal expansion. It is different
for different materials.
Solids ?????a 1/oC
Copper 1.7 10-5
Aluminium 2.4 10-5
Gold 1.4 10-5
Steel 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 C 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 1.210-5 1/C. Lets apply equation ?L
a ?L ?T ?T 25 OC 5 OC 20 C then ?L a ?L
?T 1,2 10-5 1/C 2700 m 20 OC 0,65 m 65
cm Thats a reason that expansion joints are very
necessary!
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STATES OF MATTER

1. Gases, liquids and solid states

• Examples from nature
• What does it mean states of matter?
• 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.

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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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Change of states
All substances can change their states and it
depends on temperature. Lets 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.
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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