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The Scientific Method

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Title: The Scientific Method


1
The Scientific Method
  • 1. Observe some aspect of the
    universe.
  • 2. Invent a tentative description, called a
    hypothesis, that is consistent with what you have
    observed.
  • 3. Use the hypothesis to make predictions.
  • 4. Test those predictions by experiments or
    further observations and modify the hypothesis in
    the light of your results.
  • 5. Repeat steps 3 and 4 until there are no
    discrepancies between theory and experiment
    and/or observation.

2
Science versus Pseudoscience
  • The scientific method is unprejudiced.
  • A theory is accepted based only the results
    obtained through observations and/or experiments
    which anyone can reproduce.
  • The results obtained using the scientific method
    are repeatable.
  • a theory must be falsifiable''.
  • Pseudoscience, in contrast, does not employ the
    scientific method and is constructed in such a
    fashion that its claims are not falsifiable

3
System of Units
  • Scientific International (SI)
  • Based on multiples of 10
  • meter (m) distance length of the path
    travelled by light in vacuum during a time
    interval of 1/299 792 458 of a second.
  • kilogram (kg) mass mass of the
    international prototype of the kilogram.
  • second (s) time the duration of 9 192 631 770
    periods of the radiation
    corresponding to the transition
    between the two hyperfine levels of the
    ground state of Cs 133
  • ampere (A) electric current current, if
    maintained in two straight parallel
    conductors of infinite length, of
    negligible circular cross-section, and
    placed 1 meter apart in vacuum,
    would produce between these conductors a
    force equal to 2 10-7 newton per
    meter of length."
  • kelvin (K) temperature the fraction 1/273.16 of
    the temperature of the triple point
    of water."

4
Scalars and Vectors
  • A scalar quantity has magnitude only (how much?)
  • Examples
  • Mass
  • Volume
  • Distance
  • Speed
  • A vector quantity has magnitude and direction
  • Examples
  • Displacement
  • Velocity
  • Acceleration
  • Force

5
Aristotles Universe(Geocentric)
  • Aristotle proposed that the heavens were
    literally composed of concentric, crystalline
    spheres to which the celestial objects were
    attached.
  • Each object rotated at different velocities, with
    the Earth at the center.
  • The ordering of the spheres to which the Sun,
    Moon, and visible planets were attached are shown
    to the right.

6
Stellar Parallax
  • Stars should appear to change their position with
    the respect to the other background stars as the
    Earth moved about its orbit, because they are
    viewed from a different perspective.

7
Planetary Motion
  • Most of the time, planets move from west to east
    relative to the background stars. This is direct
    motion.
  • Occasionally, however, they change direction and
    temporarily undergo retrograde motion before
    looping back.
  • (retrograde-move)

8
Planetary Motion-2
  • Retrograde motion was first explained using the
    following model devised by Ptolemy
  • The planets were attached, not to the concentric
    spheres themselves, but to circles attached to
    the concentric spheres, as illustrated in the
    adjacent diagram.
  • These circles were called "Epicycles",and the
    concentric spheres to which they were attached
    were termed the "Deferents".

9
Planetary Motion-3
  • In actual models, the center of the epicycle
    moved with uniform circular motion, not around
    the center of the deferent, but around a
    point that was displaced by some distance from
    the center of the deferent.

10
Heliocentric Model
  • Copernicus proposed that the Sun, not the Earth,
    was the center of the Solar System. Such a model
    is called a heliocentric system.
  • The ordering of the planets known to Copernicus
    in this new system is illustrated in the
    following figure, which we recognize as the
    modern ordering of those planets.
    (copernican-move)

11
Galileo Galilei
  • Galileo used his telescope to show that Venus
    went through a complete set of phases, just like
    the Moon. This observation was among the most
    important in human history, for it provided the
    first conclusive observational proof that was
    consistent with the Copernican system but not the
    Ptolemaic system.

12
Kepler- Elliptical orbits
  • The amount of "flattening" of the ellipse is the
    eccentricity. In the following figure the
    ellipses become more eccentric from left to
    right. A circle may be viewed as a special case
    of an ellipse with zero eccentricity, while as
    the ellipse becomes more flattened the
    eccentricity approaches one.
  • (eccentricity-anim)

13
Keplers Laws
  • Keplers 1st Law
  • The orbits of the planets are ellipses, with the
    Sun at one focus of the ellipse.

14
Keplers Laws
  • Keplers 2nd Law
  • The line joining the planet to the Sun sweeps out
    equal areas in equal times as the planet travels
    around the ellipse.

15
Keplers Laws
  • Keplers 3rd Law
  • The ratio of the squares of the revolution
    periods (P) for two planets is equal to the ratio
    of the cubes of their semimajor axes (R).

16
Speed
  • How fast/ How slow is it going?

Time rate of change of motion
Speed distance time
17
Constant Motion vs. Changing Motion
  • Objects motion is constant its speed and
    direction are not changing
  • Objects motion is changing its speed and/ or
    direction are changing

18
Acceleration
  • Is it speeding up, is it slowing down,
    How fast is its speed changing?

More important How is its motion changing?
19
Acceleration (cont)
  • Acceleration change in velocity
  • time

a vf - vi t
or a ? v t
20
Acceleration Due to Gravity
Some everyday observations . . .
an objects velocity increases as it falls
how an objects velocity changes depends on air
resistance
If there is no air resistance, the object will
fall freely . . .
We call it a Freely Falling Object
21
Motion with Constant Acceleration
  • Recall a vf - vi t

When the objects initial velocity is zero . . .
We say that it started from rest
Or was dropped from rest
vf a t
d ½ at2
and
22
Motion in a Circle
  • Recall that acceleration is defined as a change
    in velocity with respect to time.
  • Since velocity is a vector quantity, a change in
    the velocitys direction , even though the speed
    is constant, represents an acceleration.
  • This type of acceleration is known as
  • Centripetal acceleration
  • ac v2/r

23
Force Motion
  • Force everyday words Push or Pull

Examples
(Earths Gravity pulls down on objects)
  • Forces are Vectors

24
Recognizing Forces
  • Note The Force due to Gravity is always pulling
    down on us!
  • At-a-Distance Forces Contact Forces

25
Net Force
  • The sum of all the forces acting on an object

Net force zero
Balanced forces
Net force non-zero
Unbalanced forces
26
Newtons Laws of Motion
(Net) force causes change in motion
Net Force ? Change in Motion
Cause
Effect
27
Newtons 1st Law of Motion The Law of Inertia
An object at rest,
or in motion,
will stay at rest,
will continue in the same (straight line) motion,
unless a net, external force acts on it.
? unbalanced
? outside
28
Newtons 3rd Law of Motion
For every action - there is an equal and
opposite reaction.
Warning This popular expression of Newtons 3rd
Law can lead to confusion!!!!
  • Better!For every force one object exerts onto
    another, there is an equal opposite force
    exerted back.

29
Newtons 2nd Law of Motion
Force mass x acceleration
  • F ma

30
Relationship between Mass Weight
  • Weight is the force due to gravity on an object

w Fg
mag
w m
g
ag
31
Momentum
  • Product of the mass and velocity of an object
  • Momentum mass x velocity

p mv
32
Conservation of Momentum
  • When two objects collide

(exerting forces on each other),
their total momentum is conserved
  • Law of Conservation of Linear Momentum
  • The total linear momentum of an isolated system
    remains the same
  • if there is no external, unbalanced force acting
    on the system.

33
Conservation of Angular Momentum
Angular Momentum The momentum of rotation
  • Law of Conservation of Angular Momentum
  • The angular momentum of an object remains
    constant,
  • if there is no external, unbalanced torque
    acting on it.

34
Gravity
  • Does the rotation of the Earth cause gravity?

Does the our atmosphere/ air pressure push us
down to keep us on the ground?
Does the Moons orbit about the Earth cause
gravity?
Is there gravity on the Moon? On the Sun?
Are the astronauts in the space shuttle really
weightless?
35
Gravity is not caused by
  • Rotation of the Earth
  • Earth's atmosphere
  • Air pressure
  • Earth's magnetism

36
Law of Gravity
  • Every mass in the universe attracts (and is
    attracted by)
  • every other mass in the universe
  • by a force that we call the force of gravity.
  • Equation form of this law

(where G 6.67 x 10-11 Nm2/kg2)
37
Weightlessness
  • (Sometimes called microgravity)
  • Apparent weightlessness
  • the sensation you experience when there is no
    floor pushing up on you.

38
Conservation of Momentum
  • Law of Conservation of Linear Momentum
  • The total linear momentum of an isolated system
    remains the same
  • if there is no external, unbalanced force acting
    on the system.

39
Conservation of Angular Momentum
Angular Momentum The momentum of rotation
  • Law of Conservation of Angular Momentum
  • The angular momentum of an object remains
    constant,
  • if there is no external, unbalanced torque
    acting on it.

40
Work
  • It takes energy to do work
  • the process by which energy is transferred or
    changed from one form into another
  • Work is done when you apply a force over a
    distance

W F x d
41
Gravitational Potential Energy
  • - the energy an object has because of its
    location (in a force field)
  • position energy

Work
Energy sugar in muscles ? PotentialEnergy
of ball
Work I did lifting
PEball
PE mgh
F d PE
mag
g
42
Kinetic Energy, KE
  • - the energy an object has because of its motion
  • moving energy

KE ½ mv2
Ex Basketball Ball
? KineticEnergy of ball
Work I do pushing
43
Law of Conservation of Mechanical Energy
  • In the absence of friction
  • the sum of the kinetic energy and the potential
    energy of a system is constant.
  • (I.e., total energy is constant!)

44
Power
- time rate of energy usage How fast was the
work done?
  • Power work time

P W t
Units Watts Joule/sec
45
Thermal Energy (Heat)
  • Heat is simply thermal energy i.e., a measure of
    the kinetic energy of the atoms or molecules that
    make up a substance.
  • Heat Energy is measured in caloriesdefined as
    the heat required to raise 1 gram of water by 1 o
    C.
  • The mechanical equivalent(in joules) of a
    calorie is 1 calorie 4.186 Joules

46
Mass Energy
  • Every object contains the (mass)potential energy
    equivalent
  • E m c2
  • where c is the speed of light
  • c 3 x 108 m/s

47
Relativity Revealed
  • 1' Lecture
  • The Special Theory of Relativity tells us that
    time, distance and mass are not what we think
    they are.
  • The General Theory of Relativity shows us that
    mass warps space.

48
Relativity Revealed
  • Special Theory
  • Applies to non-accelerated frames of reference.
  • Makes two (2) assumptions
  • The is no preferred inertial frame of reference.
  • The velocity of light, c is a constant.

49
Relativity Revealed
  • What about assumptions?
  • No preferred inertial frame.
  • Speed of light is constant.
  • (c 300,000,000 m/s)

O.K. ? ??????
50
Relativity Revealed
  • Its everywhere! Its everywhere!
  • The Lorentz Factor
  • 1/v1 - v 2/c 2
  • Not important until v c, then VERY important.

51
Fundamental Principles of Temperature Heat
  • Matter is made up of particles
  • and these particles are in motion
  • Heat energy naturally flows
  • from warmer parts to cooler parts of a system
  • Conservation of (Heat) Energy
  • (First Law of Thermodynamics)

Heat Energy lost Heat Energy gained 0
52
Particles are in motion
Microscopic Properties of Substances
  • Particles are moving in all directions!
  • Particles are colliding with each other the
    walls of the container!

Temperature, T, is a relative measure of the
average KE of the particles.
53
Heat Transfer Mechanisms
1. Conduction Transfer of heat by individual
particles colliding with each other
2. Convection Transfer of heat by the large
scale movement of heated regions of a
fluid to cooler regions
3. Radiation Heat transfer by the absorption or
emission of EM radiation (mainly infrared
radiation)
54
Measuring Heat
  • Heat energy , Q
  • - thermal energy that is transferred between
    objects at different temperatures

Units joules (J) or calories
(cal)
What happens when something gains or loses
heat? 1. Temperature can change or
2. Phase can change
55
1. To change Temperature of a substance
Heat energy must be lost or gained
Q mc?T
m mass
c specific heat capacity of substance
?T change in temperature
56
Heat Changes of Phases
2. To change the Phase of a substance
Heat energy must be given off or absorbed
Q mL
Liquid - gas changes
Lv Latent Heat of Vaporization
Solid liquid changes
Lf Latent Heat of Fusion
57
Phase Change Chart
Vapor is gaining heat
Water is boiling
Water is gaining heat
Temperature (ºC)
Ice is melting
Water Vapor
Vapor only
Water only
Ice Water
Ice only
Heat added
58
2nd Law of Thermodynamics
One statement of the Second Law of
Thermodynamics
Heat does not spontaneously flow from a
low-temperature region to a high-temperature
region.
59
2nd Law of Thermodynamics
Another form of the Second Law of Thermodynamics
It is not possible to make a heat engine whose
only effect is to absorb heat from a
high-temperature region and turn all that heat
into work.
60
2nd Law- Continued
If we could design such a 100 efficient heat
engine, we could then use that heat engine to
power a refrigerator. The net result of that
combination would be to cause heat to flow from a
cold temperature to a high temperature.
61
Electricity
Electric Charge, q
Unit coulomb, C
Recall Structure of the Atom
Nucleus Positively charged
Electrons Negatively charged
q (one proton) 1.6 x 10-19 C
q (one electron) - 1.6 x 10-19 C
62
Like charges repel/ unlike charges attract
Coulombs Law The force law that describes
charge-charge interaction FkQq/r2
Electric Field The region of space around an
electric charge
63
Ohms Law
Voltage is proportional to current
voltage current x resistance
V IR I V/R R V/I
64
Series circuits
Circuit with one path.
The current must flow through the resistors one
at a time.
Therefore
  • The total resistance in the circuit is the sum
    of the individual resistances.
  • Current is the same throughout the circuit.
  • When one resistor breaks the current can no
    longer flow through any of the resistors.

65
Parallel circuits
Circuit with many paths.
The current splits to flow through the resistors.
Therefore
  • The total current in the circuit is the sum of
    the currents in each path.
  • The same voltage is provided to each path of
    the circuit.
  • When one device/ resistor is turned off, or
    breaks, the current can continue to flow
    through other paths.

66
Power, P
Recall Power is the time rate of energy usage P
E/t
Units watt, W
Electric Power current x voltage
P IV
67
Magnetism
Like poles repel, Unlike pole attract
  • Magnetic Force Field

Direction
Strength
  • Ferromagnetic Materials

Just what makes a ferromagnetic material magnetic?
68
Electromagnetism
  • A moving charge creates a magnetic field

Example The Electromagnet - coils of current
carrying wire producing a magnetic field
  • A magnetic field can exert a force on a
    moving charge

69
Electromagnetic Induction
  • The induction of an electric current in a wire
    when a nearby magnetic field changes

Example The Hand-held Flashlight
70
Electromagnetic Devices
1. Motor
A device that converts electrical energy into
mechanical energy
2. Generator
A device that converts mechanical energy into
electrical energy
3. Transformers
A device that increases or decreases the voltage
of an alternating current
71
Wave Types
Transverse Wave
A wave which consists of a series of up and
down disturbances of a medium.
Examples
Water waves
Rope waves
Light waves
Longitudinal Wave
A wave which consists of a series of compressions
and expansions disturbances of a medium.
Examples
Slinky
Sound waves
72
Wave Characteristics
l
A
  • Amplitude - the height of the wave, the
    distance from equilibrium to the maximum
    displacement of the wave
  • Wavelength, ? the distance between corresponding
    points on a wave
  • Frequency, wthe number of wave disturbances that
    occur per second
  • Wave speed, v the speed of the wave v ? w

73
Longitudinal Waves
74
Longitudinal Waves
Wavelength
75
Constructive Interference
http//www.colorado.edu/physics/2000/applets/fouri
er.html
76
Destructive Interference
http//www.colorado.edu/physics/2000/applets/fouri
er.html
77
Standing Waves
A standing or stationary wave is produced when
two waves of the same wavelength but travelling
in opposite directions interfere constructively
Longitudinal Wave
http//home.a-city.de/walter.fendt/physengl/stlwav
es.htm
78
Electromagnetic Waves
Electromagnetic waves are produced by an
oscillating or accelerated charge The changing
electric field produces a changing magnetic field
http//www.Colorado.EDU/physics/2000/applets/field
waves.html
http//www.phy.ntnu.edu.tw/hwang/emWave/emWave.ht
ml
http//home.a-city.de/walter.fendt/physengl/emwave
.htm
79
Doppler Effect
A change in pitch resulting from the relative
motion of the source of the sound and the
observer. When a source of sound is moving toward
you, the wave crests are closer together and the
pitch sounds higher. When the source of sound
is moving away from you, the wave crests are
farther apart and the pitch sounds lower.
http//home.a-city.de/walter.fendt/physengl/dopple
rengl.htm
http//www.mohawk.net/viking/physics/doppler.html
80
Electromagnetic Radiation
81
Radio Waves-- Amplitude Modulation
http//www.colorado.edu/physics/2000/applets/fouri
er.html
82
Infrared Radiation
Light whose wavelength is longer than visible
light Heat Radiation-- produced by objects
whose temperature is 300 K
83
Ultraviolet Radiation
Light whose wavelength is shorter than visible
light Higher in energy than visible
light--produces damage in organic material (e.g.,
sunburn)
84
X-Ray Radiation
Electromagnetic radiation of short wavelength
and high-energy. Produced by rapid deceleration
of electrons or other high energy processes
85
Gamma Ray Radiation
The highest energy, shortest wavelength
electromagnetic radiation. Produced by nuclear
decay or highly energetic processes.
86
Structure of the Atom
  • For at least 25 centuries, matter believed to be
    made of tiny particles -- atoms.
  • Newton thought that atoms were hard and
    indivisible.
  • Complex structure of the atom not observed until
    20th century.
  • In 1897, J.J. Thomson discovered the electron.
  • In 1911, Ernest Rutherford detected the atomic
    nucleus.

87
Bohr Model of the Atom
  • Planetary model of the atom.
  • Neutrons and protons occupy a dense central
    region called the nucleus.
  • Electrons orbit the nucleus much like planets
    orbiting the Sun.
  • Modifications
  • Only certain select radii are possible for the
    electron orbits.
  • If an electron moves in an allowed orbit, it
    radiates no energy.
  • The amount of energy required to move from one
    orbit to another is fixed.

88
Photon A particle of light
  • The photon is a unit packet of
    electromagnetic radiation
  • The photon has an energy that depends on its
    frequency

E hw (h 6.626 x 10-34 Js)
? The energy of one photon!
89
Photons
  • Electrons may exist only in orbitals having
    certain specified energies.
  • Atoms can absorb only specific amounts of energy
    as their electrons are boosted to excited states
    atoms emit only specific amounts of energy when
    their electrons fall back down to lower energy
    states.
  • The light absorbed or emitted must be in
    packets of electromagnetic radiation containing
    a specific amount of energy.
  • These packets are called PHOTONS.
  • The energy of a photon is related to the
    frequency of the electromagnetic energy absorbed
    or emitted.

90
Frequency and Energy
  • Frequency is very important in physics and in
    astronomy, where we are very often interested in
    such things as energy and temperature.
  • This is because energy is related to the
    frequency of light by

E hf
  • When writing about light, people often use the
    Greek symbol ? (pronounced noo) for frequency,
    and c for the speed of light.
  • So in astronomy you will often see the symbols ?
    and c for frequency and speed.

Light
Waves in general
c ? ?
v f?
E h ?
E hf
91
Three Types of Spectra
92
Emission Spectra
Pattern of bright spectral lines produced by an
element.
93
Photoelectric effect
94
(No Transcript)
95
Band of Stability
Chart of the Isotopes As the atomic number
increases, more neutrons are needed to make the
nucleus stable Clues to radioactivity Atomic
number of 83 and above Fewer neutrons than
protons in the nucleus Odd-Odd nuclide
96
U-238 Decay
97
Nuclear Fission
When a nucleus fissions, it splits into several
smaller fragments. Two or three neutrons are
also emitted. The sum of the masses of these
fragments is less than the original mass. This
'missing' mass (about 0.1 percent of the original
mass) has been converted into energy. Fission
can occur when a nucleus of a heavy atom captures
a neutron, or it can happen spontaneously.
98
Fission-Continued...
A chain reaction occurs when neutrons released in
fission produce an additional fission in at least
one further nucleus. This nucleus in turn
produces neutrons, and the process repeats.
99
Control of Fission
To maintain a sustained controlled reaction, for
every 2 or 3 neutrons released, only one must be
allowed to strike another uranium nucleus.
Nuclear reactions are controlled by a
neutron-absorbing material, such as cadmium or
graphite.
100
Nuclear Fusion
Fusion is combining the nuclei of light elements
to form a heavier element. In a fusion
reaction, the total mass of the resultant nuclei
is slightly less than the total mass of the
original particles.
101
Fusion
In order for fusion reactions to occur, the
particles must be hot enough, in sufficient
number and well contained. These simultaneous
conditions are represented by a fourth state of
matter known as plasma. In a plasma, electrons
are stripped from their nuclei. A plasma,
therefore, consists of charged particles, ions
and electrons.
102
Fusion
Magnetic confinement utilizes strong magnetic
fields, typically 100,000 times the earth's
magnetic field. Inertial confinement uses
powerful lasers or high energy particle beams to
compress the fusion fuel. The enormous force of
gravity confines the fuel in the sun and stars.
103
Nuclear Scales
104
Nuclear Scales--cont.
105
Fundamental Particles
106
Fundamental Particles
Quarks make up protons and neutrons, which, in
turn, make up an atom's nucleus. Each proton
and each neutron contains three quarks. There
are several varieties of quarks, as seen to the
right. Protons and neutrons are composed of two
types up quarks and down quarks. The sum of
the charges of quarks that make up a nuclear
particle determines its
electrical charge.
107
Building an Atom
Protons contain two up quarks and one down
quark. 2/3 2/3 -1/3 1 Neutrons contain
one up quark and two down quarks. 2/3 -1/3
-1/3 0 The nucleus is held together by the
"strong nuclear force," which is one of four
fundamental forces The strong force counteracts
the tendency of the positively-charged protons to
repel each other. It also holds together the
quarks that make up the protons and neutrons.
http//cgi.pbs.org/wgbh/aso/tryit/atom/

108
Antimatter
Antimatter is matter with a charge opposite to
that of what we think of as normal matter, such
as Electron, Positron, Proton, Anti-proton, and
Neutron , Anti-neutron, etc. Antiparticles act
in much the same way as do ordinary
particles Each has the same mass as their
counterparts, but the charge is opposite. If any
particle touches it's corresponding antiparticle
both would be totally annihilated leaving only
energy.
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