November 12, 2012
Joy of Science
Discovering the matters and the laws
of the universe
Key Words
Universe, Energy, Quantum mechanics,
Chemical reaction, Structure of matter
(Earth, Evolution of life, Ecosystem, Environment
will be taught in next semester)
Unless otherwise noted, all pictures are taken from wikipedia.org
Course schedule
n  Week1 (10/1) - Science as a way of knowing
n  Week2 (10/15) - The ordered Universe
n  Week3 (10/22) - Unification of the laws of the earth and the universe
n  Week4 (10/29) - Energy
n  Week5 (11/12) - Heat and the second law of thermodynamics
n  Week6 (11/19) - Electricity and Magnetism
n  Week7 (11/26) - Waves and electromagnetic radiation
n  Week8 (12/3) - The atom
n  Week9 (12/10) - Quantum mechanics
n  Week10 (12/17) - Atoms in Combination: the chemical bonds
n  Week11 (12/24 (Mon) à 12/25 (Tue)) - Chemical reactions
n  Week12 (1/7) - Modern materials
* Winter vacation starts on 12/27, Thursday
n  Week13 (1/21) - Nuclear power
n  Week14 (1/28) - The ultimate structure of matter
n  Week15 (2/4) – Group Discussion day, final report due date
Review
Review
The great chain of energy
n  Work: In scientific speaking, work is done when a force is exerted over distance
work (joules) = force (newtons) X distance (meters): W = F x d
n  Energy: the ability to do work.
If a system is capable of exerting a force over a distance, then that system
possesses energy. (è same units used for work)
n  Power: the amount of work done divided by the time it takes to do that work
power (watts) = work (joules) / time(seconds): P = W / t
Electrical power unit: watts
Work = Energy (joules) = power (watts) X time (seconds)
Review
The great chain of energy
n  Work: In scientific speaking, work is done when a force is exerted over distance
work (joules) = force (newtons) X distance (meters): W = F x d
n  Energy: the ability to do work.
If a system is capable of exerting a force over a distance, then that system
possesses energy. (è same units used for work)
n  Power: the amount of work done divided by the time it takes to do that work
power (watts) = work (joules) / time(seconds): P = W / t
Electrical power unit: watts
Work = Energy (joules) = power (watts) X time (seconds)
Energy unit in your electric bill?
A: kWh (kilowatt-hour) !
Energy (kWh) = power (kilowatt) X time (hour)
Review
Forms of energy
n  Kinetic energy: energy associated with moving objects
kinetic energy (joules) = ½ X mass (kg) X [speed (m/s)] 2
: EK = ½ X m X v 2
n  Potential energy: energy waiting to be released
gravitational potential energy, chemical potential energy, electrical potential energy,
and elastic potential energy - In any case, energy is stored, ready to do work!
gravitational potential energy (joules) = mass (kg) X g (m/s2 ) X height (m)
: EP = m X g X h
n  Heat, thermal energy, is the random kinetic energy of atoms and molecules
Particles making up all matter move around and vibrate!
- All matter is made of minute objects called atoms
- Discrete collections of two or more atoms are called molecules
n  Mass is a form of energy Einstein’s equation:
energy (joules) = mass (kg) X [speed of light (m/s) ]2
E = mc2
Interchangeability of energy
n  The flow and the form conversion of energy from the Sun to human
body
Sun
light
plants
chemical energy into
kinetic energy
chemical energy of cells
and tissues
human
muscles’ motion (kinetic E)
à climb a flight of stairs (gravitational potential E)
à stretch a rubber band (elastic potential E)
à rub hands together (Heat)
n  Energy in one form can be converted into others
The first law of thermodynamics
The first law of thermodynamics:
Thermodynamics: the study of the movement of heat – this term used
for the science of heat, energy, and work
System:
A system can be thought of an imaginary box into which you put some
matter and energy that you would like to study
- open system: if the system under study can exchange
matter and energy with its surroundings, the system is open.
Ex) a pan full of water being heated on a stove
- closed or isolated system: if matter an energy in a system do
not freely exchange with their surroundings, the system is closed.
Ex) the system of Earth and it’s primary energy source, the Sun
Conservation law: if a physical attribute is constant and unchanging
therefore it is conserved, there is an associated conservation law
The first law of thermodynamics:
The first law of thermodynamics
n  The first law of thermodynamics:
In an isolated system the total amount of energy, including
heat, is conserved
è The law of energy conservation
è The kind of energy in a given system can change, but the total
amount cannot!
The first law of thermodynamics:
Energy is conserved
n  Energy is something like an economy with an absolutely
fixed amount of money!
You can earn it, store it in a bank or under your pillow, and spend
it here and there.
But the total amount of money doesn’t change because it passes
through your hands.
n  For example, when a bungee jumper launches herself into
space, some of the gravitational potential changes into kinetic
energy, some into elastic potential energy, and some into the
increased temperature of the surroundings.
è But the total amount of energy, in a closed system, should be
the same amount as the energy when you started with. (gravitational) potential
Heat and the second law of
thermodynamics
Why is it easier to tear something
down than to build it
Temperature, heat transfer, convection, conduction,
radiation, absolute zero,
second law of thermodynamics, efficiency, entropy
Contents
n  Introduction
n  Three modes of heat transfer
n  The second law of thermodynamics
1. Introduction
Nature’s direction
n  Throughout the universe, there are some natural tendency for
things to become less orderly with time!
n  The tendency of all systems to evolve from improbable to more
probable states accounts for the directionality that we see in the
universe around us!!!
Ex) Perfume scent disperses through a room when the
perfume bottle is open
Billiard balls tend to be scattered than get together
Terms with heat
n  Atoms never sit still, but move always while distributing
their kinetic energy – so called, thermal energy or internal
energy.
n  In order to understand the nature of heat and its movement,
let us define three terms first: Heat, Temperature, and Specific
heat capacity.
Heat
n  Heat: A form of energy that moves from a warmer object to a
cooler object
à Heat is, therefore, energy in motion.
n  Calories: A common unit of energy defined by
“ the amount of heat required to raise 1 gram of roomtemperature water by 1 degree Celsius in temperature”
(In science, room temperature is usually taken to be either 20 or 25
degrees Celsius)
Temperature
n  Temperature: A term that compares how vigorously atoms in a
substance are moving and colliding in different substance
à The larger the temperature difference between two objects,
the more rapidly heat is transferred.
Temperature
n  Temperature: A term that compares how vigorously atoms in a
substance are moving and colliding in different substance
à The larger the temperature difference between two objects,
the more rapidly heat is transferred.
n  Temperature scales: Every scale requires two easily reproduced
temperatures for calibration – freezing and boiling points of pure water
* Celsius scale : 0 and 100 degrees for freezing and boiling
(degrees Celsius: most common)
* Kelvin scale : same degrees as Celsius, with 100 increments
(Kelvins: scientific) between the freezing and boiling points of water
0 oC = 273.15 K
100 oC = 373.15 K
* 0 K: “absolute zero” – the temperature at which it is impossible to
extract any heat
Temperature conversions
n  It is often necessary to convert from one temperature scale to
another
Fahrenheit scale (degrees Fahrenheit): 32 and 212 degrees for
freezing and boiling, respectively
degrees F = ( 9/5 X degrees C ) + 32
degrees C = (degrees F – 32) X 5/9
Specific heat capacity
n  Specific heat capacity: A measure of the ability of a material to
absorb heat
“ The quantity of heat required to raise the temperature of 1 gram
of that material by 1 degree Celsius”
Specific heat capacity
n  Specific heat capacity: A measure of the ability of a material to
absorb heat
“ The quantity of heat required to raise the temperature of 1 gram
of that material by 1 degree Celsius”
n  When we boil water in a copper pot,
- it doesn’t take long to raise the temperature of a copper pot to above
the boiling point of water, because copper- like most metals- heats up
rapidly as it absorbs heat;
- it takes much more time to boil water in the pot
èWater absorbs 10 times more heat per gram than copper to raise its
temperature
à The ability of water to store thermal energy is bigger than that of
copper. In fact,
Water has the largest heat capacity of any common substance.
2. Three modes of heat transfer
Three modes of heat transfer
Heat transfer
n  You can not prevent heat from moving from an object at high
temperature to its cooler surroundings!
n  Heat transfer: The process by which heat moves from one
place to another
n  There are three basic mechanisms of heat transfer:
Conduction, Convection, and Radiation
Three modes of heat transfer
Conduction n  If a piece of metal is heated at one end, the atoms and their
electrons at that end begin to move faster
à They vibrate and collide with other atoms father away from
the heat source
à A chain of collision occurs farther and farther
èèEnergy is transferred to molecules farther away from the
heat source
Three modes of heat transfer
Conduction (cont’d) n  Conduction: An energy transfer mode between bodies of
matter due to temperature difference through the action of
individual atoms or molecules that are linked together by
chemical bonds
n  Thermal conductivity: The ability to transfer heat from one
molecule to the next by conduction. Materials differ in their
thermal conductivity.
* Heat conductor: It moves heat rapidly.
Ex) metals – copper, silver, aluminum.
* Heat insulator: It resists the flow of heat transfer.
Ex) glass, paper, wood
Three modes of heat transfer
Convection
n  Convection: The transfer of heat by the bulk of fluid, such as air
or water.
n  Convection cell: Each of regions of rising and sinking fluid.
Ex) Boiling water in a pot on a stove has a rolling, churning
motion as the water moves and mixes through convection,
and the places where water bubbles up and where bubbles
tend to collect are convection cells.
n  Heat is carried from the burner through the convection of the
water and is eventually transferred to the atmosphere.
è Convection is thus a very efficient way of transferring heat Three modes of heat transfer
Radiation
n  Radiation: The transfer of heat by electromagnetic radiation, a
form of wave energy
Ex) Glowing red hot above a fireplace or an electric heater:
infrared radiation
è You perceive heat b/c of the energy that the infrared
radiation carries to your hand
Three modes of heat transfer
Radiation
n  Radiation: The transfer of heat by electromagnetic radiation, a
form of wave energy
Ex) Glowing red hot above a fireplace or an electric heater:
infrared radiation
è You perceive heat b/c of the energy that the infrared
radiation carries to your hand
n  All objects in the universe radiate energy in this way
: Under normal circumstances, as an object gives off radiation to
its surroundings, it also receives radiation from those
surroundings
è No net loss of energy under a kind of equilibrium set up
n  Radiation is the only kind of energy that can travel through the
emptiness of space.
n  In the real world, all three types of heat transfer occur all the time
Energy transfer
n  Convection
n  Convection zone
n  Conduction
n  Radiation
Convection
Conduction zone
Radiation
Conduction
3. The second law of thermodynamics
The second law of thermodynamics
The second law of thermodynamics
n  There is a direction to energy’s flow!
n  The second law of thermodynamics states the common sense of
the direction of energy flow
n  The second law of thermodynamics in different statements
1. Heat will not flow spontaneously from a cold to a hot body
2. You cannot construct an engine that does nothing but convert
heat to useful work
3. Every isolated system becomes more disordered with time
è These three statements appear differently, but they are actually
logically equivalent!!
The second law of thermodynamics
1. Heat will not flow spontaneously
from a cold to a hot body
n  This statements describe the behavior of two objects at different
temperatures:
From everyday observations, we find that in our universe
heat flows in only one direction, from hot to cold
n  This statement explains at the molecular level:
Faster-moving molecules tend to share their energy with
slower-moving ones by collisions
n  This statement tells us that:
If you wish to cool something down, this action cannot take
place “spontaneously”
è you must supply energy
à A refrigerator will not work unless it is plugged in!
The second law of thermodynamics
2. You cannot construct an engine that does
nothing but convert heat to useful work
n  Energy can be defined as the ability to do work!
n  This second statement tells us that
“ Whenever energy is transformed from heat to another type, some
of that heat must be dumped into the environment and is
unavailable to do work” è perpetual motion is impossible!
Source Energy
Engine
Heat
Work
electricity, potential
energy, …
Heat loss
Environment
The second law of thermodynamics
2. You cannot construct an engine that does
nothing but convert heat to useful work (cont’d)
n  For example, when fossil fuels are burned to produce a high-
temperature reservoir and generate electricity, a large portion of
energy must simply be thrown away
* High
temperature reservoir: Exploding hot-gas mixture
* Low temperature reservoir: Atmosphere into which the heat of
compression is dumped
Fossil fuels
Heat
Engine
High
temperature
Heat loss
Environment
Low
temperature
Work
electricity, potential
energy, …
The second law of thermodynamics
2. You cannot construct an engine that does
nothing but convert heat to useful work (cont’d)
n  Efficiency quantifies the loss of useful energy
“ Efficiency is obtained by comparing the temperature difference
between the high temperature and low temperature reservoirs with
the temperature of the high temperature reservoir”
efficiency (percent)
= (hot temperature – cold temperature)/ hot temperature X 100
The second law of thermodynamics
3. Every isolated system becomes more
disordered with time
n  This statement describes the tendency of systems all around us
to become increasingly disordered
Ex) A carefully cleaned room gets messy.
A brand new car becomes dirty and scratched.
All our bodies gradually get old and wear out.
The second law of thermodynamics
3. Every isolated system becomes more
disordered with time (cont’d)
n  The meaning of “order”: A number of objects – any small like atoms
or big ones like automobiles - contained a system are positioned in a
completely regular and predictable pattern
n  The meaning of “disorder”: Objects in a system are randomly
situated, without any obvious pattern
n  Highly ordered configurations are less probable: Almost possible
configurations are disordered
è Ordered (low or small entropy): low probability
Disordered (high or large entropy): high probability
* Definition of Entropy: a measure of disorder
The second law of thermodynamics
The second law of thermodynamics
n  “The entropy of an isolated system remains constant or
increases.”
The second law of thermodynamics
The second law of thermodynamics
n  Entropy: It was named after the Greek word for a transformation
Definition of entropy: a measure of disorder
n  In probability theory,
the entropy of any arrangement of atoms is related to the
number of possible ways that you can achieve that arrangement
n  Examples of increase of entropy:
- Without careful chemical and physical controls, atoms and
molecules tend to become more intermixed
- Without careful driving, collections of automobiles tend to
become more disordered
The second law of thermodynamics
The second law of thermodynamics
n  “The entropy of an isolated system remains constant or
increases.”
Refrigerator!???
The second law of thermodynamics
The second law of thermodynamics
n  “The entropy of an isolated system remains constant or
increases.”
: One part of a system can become more ordered, while
another part of the system becomes more disordered.
Ex) A freezer with a power code
è The system’s total entropy must increase!
Quiz 1 n  Eventually, all energy generated on the Earth is returned to
space as
1. heat
2. gravitational energy
3. work
4. potential energy Quiz 1 n  Eventually, all energy generated on the Earth is returned to
space as
1. heat
2. gravitational energy
3. work
4. potential energy Quiz 2
n  Which of the following statements is not consistent with the
second law of thermodynamics?
1. All isolated systems will tend to remain ordered indefinitely
2. Heat will not flow spontaneously from a cold body to a hot
body
3. No engine is one hundred percent efficient in converting
energy to work
4. The evolution of more complicated forms of life on Earth
does not annul the second law Quiz 2
n  Which of the following statements is not consistent with the
second law of thermodynamics?
1. All isolated systems will tend to remain ordered indefinitely
2. Heat will not flow spontaneously from a cold body to a hot
body
3. No engine is one hundred percent efficient in converting
energy to work
4. The evolution of more complicated forms of life on Earth
does not annul the second law Quiz 3 n  A fire transfers most of its heat by
1. convection
2. conduction
3. radiation
4. infusion
Quiz 3 n  A fire transfers most of its heat by
1. convection
2. conduction
3. radiation
4. infusion
Quiz 4 n  All isolated systems will spontaneously tend toward disorder.
The phenomenon is referred to as
1. thermal inefficiency
2. heat transfer
3. entropy
4. thermal conductivity
Quiz 4 n  All isolated systems will spontaneously tend toward disorder.
The phenomenon is referred to as
1. thermal inefficiency
2. heat transfer
3. entropy
4. thermal conductivity
Next topic is,
Electricity and Magnetism
: Chapter 3
www.sci.hokudai.ac.jp/~epark/ekpark_e.html