Some physics: Energy, what exactly is it? (some physics)
PHYS105: Physics for Decision Makers: Global Energy Crisis PHYS105:
Physics for Decision Makers, Eno, F14 1
Slide 2
Demos J1-21: electrostatic attraction and repulsion I5-02
transformation of mechanical energy into heat C6-02 inclined plane
friction block PHYS105: Physics for Decision Makers, Eno, F14
2
Slide 3
A little physics Force, Energy, Work, Power PHYS105: Physics
for Decision Makers, Eno, F14 3 Dont be afraid: it wont be
hard
Slide 4
Warning PHYS105: Physics for Decision Makers, Eno, F14 4 To
paraphrase a quote perhaps falsely attributed to George Bernard
Shaw Americans and British are one people separated only by a
common language Physicists and non-physicists are one people
separated only by a common language. Force, Energy, Work,
Power
Slide 5
Forces PHYS105: Physics for Decision Makers, Eno, F14 5 A push
or a pull Some force in your day-to-day life Tension in a rope
Gravity normal force Friction Electrostatic force
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Fundamental Forces 15 March 2012 6 Particle physicists think of
it as this: Matter: Quarks (protons) leptons (electron) Force boson
matter Some more force boson
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And we only have four of them 15 March 2012 7 Electricity and
Magnetism (QED) photon Strong Force (QCD) gluon Weak Force W&Z
bosons
http://www.dreamstime.com/powerplant-infrastructure-stock-photo-imagefree242420
gravity
Slide 8
Everyday forces in terms of fundamental forces PHYS105: Physics
for Decision Makers, Eno, F14 8 Some force in your day-to-day life
Tension in a rope: electromagnetism normal force: electromagnetism
Friction: electromagnetism Electrostatic force: electromagnetism
Gravity: gravity What are some other forces you can think of?
Slide 9
PHYS105: Physics for Decision Makers, Eno, F14 9 Turn in your
reactor form If you have a bit of physics phobia, please dont panic
during this lecture! There will only be about 5 lectures this
semester that have this much physics.
Slide 10
electromagnetism PHYS105: Physics for Decision Makers, Eno, F14
10 Knowledge and sophistication of theory has evolved with time,
but old way of thinking are still useful. Force field. Two charged
objects interact via a field, called the electric field. Each
charged particle makes a field. When the other enters the field,
the other feels a force. Each therefore makes a force on the other
(electric force). Magnetic dipoles (such as bar magnets) interact
in a similar way via magnetic fields, to create magnetic forces on
each other. Useful to think about it this way when thinking of the
electricity in our house. Gauss: oscillating electric and magnetic
fields (electromagnetic waves) are light. They oscillate because
their electric and magnetic fields get bigger and smaller, like the
heights of waves in the ocean. Useful when thinking about global
warming, since this involves light. Einstein, Planck: light is a
particle, not just a wave, and the possible energies it can have
are quantized. Photon is the particle of light. Useful when
thinking about solar panels. Max Planck: 1858-1947 Carl Gauss:
1777-1855 Albert Einstein: 1879-1955
Slide 11
Waves PHYS105: Physics for Decision Makers, Eno, F14 11 Have
amplitude, wavelength (), and period (T) The wavelength determines
how it interacts with matter (including our atmosphere). We will
discuss this in more detail later. ColorWavelength (nm) Wavenumber
(cm -1 ) Blue400-500157,000 red600-70090,000 infrared1,000,000 -
700 60-90,000 Light can have any wave length The period is related
to the wavelength via Where c is the speed of light.
Slide 12
Photons PHYS105: Physics for Decision Makers, Eno, F14 12
ColorWavelength (nm) Wavenumber (cm -1 ) Energy (eV) Energy (J)
Blue400-500157,00034.8x10 -19 red600-70090,00023.2x10 -19
infrared1,000,000 - 700 60-90,000 They may not have any energies.
Possible energies are the fundamental energy multiplied by an
integer. The fundamental energy is related to the wavelength and a
number called Plancks constant. This is related to the
particle-ness of the light (photon) in Quantum Mechanics. h is
called plancks constant. h=6.6x10 -34 Js
Slide 13
Force, Work, Energy PHYS105: Physics for Decision Makers, Eno,
F14 13 We divide forces into different types (strong, weak,
E&M, gravity). We can also divide energy into different types.
Roughly, two types of energy: Associated with an objects motion
Associated with (certain kinds of) forces acting on the object
(between the object and other objects. )
Slide 14
motion energy PHYS105: Physics for Decision Makers, Eno, F14 14
Some examples, kinetic energy is the energy due to the bulk motion
of the object: Moving car A running person A falling rock A
particularly important example The random motion of molecules in a
material (heat energy) Usually only the energy associated with the
bulk motion of the object is called kinetic, while this kind is
called thermal.
Slide 15
Units for energy PHYS105: Physics for Decision Makers, Eno, F14
15 Joule = 1 kg m 2 /s 2 - Metric unit of energy kWh = 1000 Joule/s
for one hour = 3,600,000 J = 3.6 MJ calorie = energy to raise
temperature of 1 g of water by one degree C calorie = 4.184 J 1
Calorie (food) = 1 kcal = 1,000 calories =is the equivalent energy
to a 100w light bulb on for about 7 minutes BTU (British Thermal
Unit) = energy to raise temperature of 1 lb of water by one degree
F = 1,055 J = 0.25 Kcal 1eV. Energy acquired by an electron when
its potential changes by 1V. 1eV = 1.6x10 -19 J Quad (quadrillion
BTUs) = 10 15 BTU = 1.054 EJ (E=10 15 )
Slide 16
KE and Conversion Practice PHYS105: Physics for Decision
Makers, Eno, F14 16 A person of mass 60 kg is moving at a speed of
1 m/s. What is their kinetic energy in Joules? What is their
kinetic energy in calories?
Slide 17
Voting cards PHYS105: Physics for Decision Makers, Eno, F14 17
Which particle has a larger kinetic energy 1)One with a mass of 1
kg moving at 2 m/s 2)One with a mass of 2 kg moving at 1 m/s
Slide 18
Potential Energy PHYS105: Physics for Decision Makers, Eno, F14
18 Potential Energy (PE) comes from forces between objects. Stored
in a force field. Think of when you have to apply a force to keep
together or pull them apart. Potential energies only happen for
forces whose value depends only on the objects position (gravity,
electric force). These forces are called conservative force. It
does not apply to other forces (especially friction). PE due to
gravitational forces between objects PE due to electrical forces
between charged objects PE stored in coiled or extended springs PE
in chemical bonds of molecules PE in nuclear bonds of nuclei
Sometimes these are given specialized names like chemical energy,
gravitational potential energy, nuclear energy etc. Some
examples:
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Potential Energy PHYS105: Physics for Decision Makers, Eno, F14
19 Potential Energy is related to (certain kinds of) forces, call
conservative forces, acting on an object. If there is a force
acting on an object, some other object must be causing that force.
So potential energies are related to configurations of objects.
Sometimes there are simple formulas for the change in PE when the
the configuration is changed.
Slide 20
Potential Energy practice PHYS105: Physics for Decision Makers,
Eno, F14 20 5 m A person with a mass of 60 kg climbs stairs so that
their height above the ground changes by 5m. What is their change
in gravitational potential energy? What if they go down the
stairs?
Slide 21
Conservation of Energy PHYS105: Physics for Decision Makers,
Eno, F14 21 Emmy Noether For a closed system, if there are no
external forces acting on the system, the total amount of energy in
that system can not change. One kind of energy can change to
another type of energy. But if you sum all the types of kinetic and
potential energy, the sum will always be the same.
Slide 22
Energy Equivalents PHYS105: Physics for Decision Makers, Eno,
F14 22
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PHYS105: Physics for Decision Makers, Eno, F14 23
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PHYS105: Physics for Decision Makers, Eno, F14 24
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Do you have some understanding of what energy is? PHYS105:
Physics for Decision Makers, Eno, F14 25
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Energy and Us PHYS105: Physics for Decision Makers, Eno, F14 26
Lets take a quick tour of how the US uses energy
Slide 27
Which source of energy do we use the most? 1.Coal 2.nuclear
3.Petroleum 4.Natural gas 5.Renewable energy sources (solar,
wind,etc) PHYS105: Physics for Decision Makers, Eno, F14 27
Slide 28
What fraction of our energy usage is in transportation 1.5%
2.25% 3.50% 4.80% PHYS105: Physics for Decision Makers, Eno, F14
28
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Energy by source and use PHYS105: Physics for Decision Makers,
Eno, F14 29 http://www.eia.gov/energyexplained/
Slide 30
Quad: 1% of US consumption/day PHYS105: Physics for Decision
Makers, Eno, F14 30
Slide 31
What is the leading user of energy in our home? PHYS105:
Physics for Decision Makers, Eno, F14 31 1.Space Heat 2.Air
Conditioning 3.Refrigerator 4.Water heating 5.Lighting
6.Electronics
Slide 32
Energy in the home PHYS105: Physics for Decision Makers, Eno,
F14 32 Space Heat 10% Air Conditioning 16% Related Heat/cool(fans
etc.) 5% Refrigerator 14% Other Kitchen appliances 13% Water
heating 9% Lighting 9% Electronics 7% Laundry 7% Miscellaneous 10%
US residential electrical use
Slide 33
What is the leading source of electricity in MD? PHYS105:
Physics for Decision Makers, Eno, F14 33 1.Coal 2.Nuclear 3.Natural
gas 4.Wind 5.solar
Slide 34
Maryland Energy Supply PHYS105: Physics for Decision Makers,
Eno, F14 34 http://www.eia.gov/state/?sid=md MD ranking in energy
use per capita: 40!!!
Slide 35
Work PHYS105: Physics for Decision Makers, Eno, F14 35 Word of
warning: if it can be tweeted, it probably is not the full story. A
force does work on an object when the force is applied to the
object while the objects position changes.
Slide 36
d PHYS105: Physics for Decision Makers, Eno, F14 36 5 m For
this person, portion of path along the direction of the
gravitational force is 5 m. Take direction of force. Draw a line.
See how much the position changed measured relative to that
line.
Slide 37
Voting cards PHYS105: Physics for Decision Makers, Eno, F14
37
Slide 38
Work-Energy theorem PHYS105: Physics for Decision Makers, Eno,
F14 38 If you calculate the work for all forces applied to an
object and sum them up, the result will tell you how much the
kinetic energy of the object will change.
Slide 39
What to remember PHYS105: Physics for Decision Makers, Eno, F14
39 Work, which is the force applied as an object changes position
times the distance moved, results in a change of energy for the
object. Force is applied to an object, the object changes position
-> energy of the object changes.
Slide 40
PHYS105: Physics for Decision Makers, Eno, F14 40 If energy is
conserved, how can there be an energy crisis? Be sure you can
answer this question by the first exam.
Slide 41
Conservation of energy: heat production PHYS105: Physics for
Decision Makers, Eno, F14 41 The answer will be related to this
slide. Demo i5-02
Slide 42
Friction PHYS105: Physics for Decision Makers, Eno, F14 42 Two
types of Friction Static: between two surface that are not sliding
Kinetic: between two surfaces moving with respect to each other
Static Friction is larger Demo c6-02 Friction is everywhere!!! Can
you give me examples of friction?
Slide 43
Friction microscopic view PHYS105: Physics for Decision Makers,
Eno, F14 43 Molecules interact via residual electrostatic forces.
Friction is the sticking and unsticking of modules (kind of like
Velcro) Depends on the roughness Much of the work done by friction
turns into random motion of molecules (heat)
Slide 44
Voting cards PHYS105: Physics for Decision Makers, Eno, F14 44
When I walk across this stage, is the gravitational force doing
work? 1)Yes 2)No
Slide 45
PHYS105: Physics for Decision Makers, Eno, F14 45 Is there any
friction involved? 1)Yes 2)no
Slide 46
PHYS105: Physics for Decision Makers, Eno, F14 46 Is it static
or sliding 1)Static 2)sliding
Slide 47
Power PHYS105: Physics for Decision Makers, Eno, F14 47
Sometimes we care about the total amount of energy we use.
Sometimes we care about the rate at which we use energy. Sometimes
we care about both. Special name for rate of energy use: Power
Slide 48
Energy and Power PHYS105: Physics for Decision Makers, Eno, F14
48
Slide 49
Person Power PHYS105: Physics for Decision Makers, Eno, F14 49
A typical person can do work at a rate of about 100 Watts (J/s)
Humans burn energy at a rate of about 1.6x10 13 Watts. World
population is about 6x10 9 people. The US burns energy at a rate of
3.3x10 12 Watts. The US population is 3.2x10 8 people.
Slide 50
Voting cards PHYS105: Physics for Decision Makers, Eno, F14 50
kW-hr is a unit of: 1)Force 2)Energy 3)Work 4)Power 5)None of the
above
Slide 51
Force, Energy, Work Power PHYS105: Physics for Decision Makers,
Eno, F14 51 Force, Energy, Work, Power Discuss with your neighbors
what each exactly is, and why they are not the same thing.
Slide 52
Work and potential energy PHYS105: Physics for Decision Makers,
Eno, F14 52 Near the surface of the earth (dont try this if you are
an astronaut!) Change in potential energy when you lift an object a
height h? The potential energy for a conservative force is the
negative of the work done by that force when the object is
moved.
Slide 53
Work-Energy theorem PHYS105: Physics for Decision Makers, Eno,
F14 53 If you calculate the work for all forces applied to an
object and sum them up, the result will tell you how much the
kinetic energy of the object will change. If we divide the works
into those due to conservative and nonconservative forces, and
remembering that W conservative =-PE
Slide 54
Conservation of Energy PHYS105: Physics for Decision Makers,
Eno, F14 54 If work causes energy to change, it stands to reason
that, if there are no external forces, the total amount of energy
is constant. However, it can change form due to internal forces.
Emmy Noether Consider the earth and a person holding a ball as a
object. Neglect any forces from the outside universe (the sun for
example). Then the total energy in this object is fixed. If the
person lets go of the ball, the potential energy of the ball turns
into exactly the same amount of other kinds of energy (velocity of
the ball plus a small additional heat energy in the ball and
surrounding air) Consider the earth (with a mountain on it) and a
person at the base of the mountain. When the person climbs a
mountain, some of the chemical energy stored in her body becomes
their gravitational potential energy (and maybe some heat in them
and the air and earth around them).
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PHYS105: Physics for Decision Makers, Eno, F14 55
Slide 56
What you should have learned PHYS105: Physics for Decision
Makers, Eno, F14 56 Be able to define force, energy, work, power
and explain the relationship between them. Given Chart A below,
convert energies given in one unit to another unit Given a power
and an amount of time, be able to calculate the amount of energy
used. Define and give examples of kinetic and potential energy Know
the amount of power a typical person can produce Know the amount of
power currently produced in the world Know the population of the
world (to one significant digit) Explain why understanding the
electromagnetic force is so important when considering world energy
use Know the wave lengths of visible light (blue-red). Know the
wavelengths of infrared light. Given Plancks constant and the
wavelength of a color of light, calculate the energy of a single
photon. Know the formula for the change in gravitational potential
energy when the distance that object is above the ground is
changed. Do simple calculations using this formula. Explain what
physicists mean when they say conservation of energy Know the
fraction of US energy use that comes from petroleum, from natural
gas, and from coal. Know the fraction of US energy use that is used
for transportation and for electric power generation. Explain the
difference between static and kinetic friction and recognize when
each is occurring.