Transcript The BIG Picture

Conceptual Physics
Lesson 1: The BIG Picture
We begin with a little philosophy…
There are schools of philosophy that maintain…
• The only reality we can be sure of is that within our
individual minds (eg. Kant, the Idealists)
• The only reality is that which we can observe with our
senses or measure with our instruments (eg. Empiricists)
• The physical world provides evidence of a non-physical
world that exists beyond the measuring capacity of our
instruments (eg. Aristotle, Aquinas)
Natural Philosophy
Known
Properties
Of Physical
World
Metaphysics
Self
Unknown
Properties Of
Physical
World
Possible
Non-Physical
World
Our approach:
• There is a physical reality exterior to our minds, which can
be analyzed and understood by the sciences of nature,
particularly, physics
• While allowing for possible non-physical reality, we will
confine our studies to the physical world
• We acknowledge that there are properties of the physical
world we do not yet understand, and the near-certainty
that there are properties we have not yet discovered. We
may speculate on these.
Conceptual Physics
Did You Know…
The Tabloid News of Physics
95% of the Universe is Missing!
Adding up all the observable stuff in the cosmos we have
•0.03% heavy elements (everything except hydrogen and helium)
•0.3% neutrinos (subatomic particles that are a by-product of solar
fusion)
•0.5% stars (There are about 71022 stars in the universe)
•4% free hydrogen and helium
We can only account for 5% of what we believe is out there!
•We conjecture that 30% of the remainder is dark matter, a form of
matter that helps hold galaxies together, and only interacts with
normal matter via gravity
•The remaining 65% is dark energy, a seeming force which is pushing
galaxies apart from one another at an accelerating rate
The universe is expanding at an ever increasing pace! Is our
end to be a lukewarm muddle of maximum entropy?
Time stops at the borders of black holes! Nobody knows what
goes on down there!
Empty space is a writhing mosh pit of virtual particles!
Subatomic particles can interact faster than the speed of
light!
The ultimate physical reality may consist of vibrating 11dimensional strings!
It’s possible that our universe is just one of an infinite
number of universes that interact gravitationally!
Conceptual Physics
Physical Existence
String Theory (??)
The Stuff of Existence
Loose
Packaged
Energy
Matter
Relativity
(E = mc2)
Fields (Stationary)
&
Waves (Traveling)
Subatomic
Particles
(“Stationary”
Or Traveling)
Quantum
Mechanics,
(Wave/Particle
Duality)
The 4 (5) Forces:
Gravity
Electromagnetic
Strong Nuclear
Weak Nuclear
(Dark Energy)
Atomic
Constituents:
Protons,
Neutrons
& Electrons
(Attraction/Repulsion)
Electromagnetism,
Light, Astrophysics,
Nuclear Physics
Kinetic Energy
Atoms
Condensed
Matter,
Planetary
Science
Thermodynamics,
Mechanics, Sound
Molecules
Chemistry
Crystals
Electronics,
Computers
Organic
Molecules
Life
Biology
Conceptual Physics
Why Math & Calculations
Normal Physics Courses are heavy with calculations
In Conceptual Physics we minimize the calculations, but
some skill in physical calculations is required
There are key physical relationships you need to know
(eg. force = mass * acceleration, energy = force *
distance), as well as key concepts like vectors
Energy fields and matter particles do not have little
formula rule books that dictate their behavior—they
simply act as their nature drives them to act. But we
observers have found physical laws that consistently
predict energy and particle behavior—to within the
accuracy we can measure things
Our measurements become increasingly sensitive. If we
find discrepancies between observation and behavior,
we need to refine—or completely change—our
mathematical models to realign to physical
measurements
For example, Einstein’s Special Theory of Relativity is a
refinement of Newton’s Laws of Motion for high speed
objects, but it radically altered our understanding of
the universe.
The discovery of atomic structure forced physics to
radically change its approach to very small scale
physics—giving rise to quantum mechanics
Conceptual Physics
Units of Physical Measurement
There is a bewildering array of physical units (eg.
pascals, amps, newtons, ohms, joules, etc.) we
encounter in undergraduate physics that are utilized
in specialized sub-disciplines like electronics, fluid
dynamics or thermodynamics
Almost all of these can be reduced to simpler units
involving: length (meters, m), time (seconds, sec),
mass (kilograms, kg), charge (Coulombs, C), and
Temperature (degrees Kelvin, K)
For example: (in the MKS unit system)
Force:
Energy:
Voltage:
Resistance:
newtons = kg m / sec2
joules = kg m2 / sec2
volts = kg / C*sec2
ohms = kg / C2*sec
When making calculations, keeping track of units is
important:
• You want to know what your answer signifies (is
it energy, volts, pressure, etc…)
• It helps you check for mistakes in reasoning (eg.
if you expect volts and end up with ohms)
• It protects your Mars Orbiter from missing the
planet (this really happened…)
Conceptual Physics
Formulae
Notation (MKS units):
t = time (seconds, sec)
d = distance (meters, m); h: height, z: depth
m = mass (kilograms, kg)
v = speed (meters/second)
c = speed of light in a vacuum
a = acceleration (meters/second2)
g = acceleration due to gravity (earth surface)
2
F = force (newton = kg m/sec )
p = momentum (kg m/sec)
E = energy (kg m2/sec2) = work = KE = PE = thermal & chemical energy (calories)
P = power (watt = kg m2/sec3)
Q = charge (coulombs); R =resistance (W, ohms)
I = current (amp = coulombs/sec)
V = voltage (volt = watts/amp = kg m2/(amp sec3)
l = wavelength (meters/cycle)
f = wave frequency (Hertz, Hz = cycles/sec)
A = Area (m2)
V = volume (m3)
r = Density (kg/m3)
n = index of refraction (unitless)
2
P = Pressure [ pascal = kg/(m*sec ) ]
T = temperature (K, degrees Kelvin)
Formulae:
Distance
Velocity
d = vt;
v = at
Force
F = ma;
Momentum
Impulse
p = mv
Momentum of a photon: p = h/l = hf/c (h = Planck’s constant)
FDt = Dp = D(mv) = total change of momentum due to a given force
d = at2/2
For non-zero initial speed v0: d = v0t + at2/2
For non-zero initial speed v0: v = at + v0
No change of motion if: S F = 0
Hooke’s Law (spring restoration): F = -k Dx
Gravitational Attraction: F = G m1 m2 / d2
Electrostatic Attraction: F = k q1 q2 / d2 (Not k in Hooke’s Law)
Weight at Earth’s surface; weight = F = mg (g = 9.8m/sec2)
Energy: Work W = Fd
Energy of photon: E = hf
(h = Planck’s constant)
2
Kinetic Energy: KE = ½ mv Gravitational Potential Energy: PE = mgh (earth surface, h = height)
Heat transfer: Q’ = CSHmDT Einstein’s energy equation:
E = mc2
Power
P=W/t
Electrical Power P = IV (watts = joules/sec)
Wave frequency: f = (1 / wave_period) (unit: Hz = sec-1, cycles per second)
Relationship between speed (v), frequency (f) and wavelength (l): fl = v (light: fl = c)
Wavelength of a particle: l = h/mv = h/p (h = Planck’s constant)
Speed of light in a transparent medium with index of refraction n: v = c / n
Density
Pressure
r=m/V
Current
I=Q/t
Engine_efficiency = 100% * (Thigh – Tlow ) / Thigh
P=F/A
Pressure at depth z: P = r g z
n = #gas moles
Ideal Gas Law: P V / T = nR = constant for #moles
R = Universal Gas Constant (not electric resistance)
Resistance (R): V = I R
Uncertainty Principle: Dx Dp > h, DE Dt > h (h = Planck’s constant)
Special Relativity factor: f = sqrt( 1 – v2/c2 ) < 1,
time_obs = f t,
mass_obs = m / f
Conceptual Physics
Web Resources
Textbook’s student web site
http://bcs.wiley.com/he-bcs/Books?action=index&itemId=0471150584&bcsId=1907
Hyperphysics: Good resource:
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
Wikipedia: For anything (trust but verify):
http://en.wikipedia.org/wiki/Main_Page
Powers of Ten:
http://microcosm.web.cern.ch/Microcosm/P10/english/welcome.html
http://www.youtube.com/watch?v=s1jd8AgjP9k
http://www.powersof10.com/
Atomic Orbitals:
http://www.chemguide.co.uk/atoms/properties/atomorbs.html
http://www.falstad.com/qmatom/
http://www.chemistry.wustl.edu/~edudev/Orbitals/movie.html
Fun Science & Optical Illusions:
http://www.skytopia.com/project/illusion/illusion.html
http://www.skytopia.com/