Day 08

flinkexistenceMechanics

Oct 27, 2013 (4 years and 12 days ago)

100 views

Announcements


Exam 2 is scheduled for Thursday March 7, three weeks
from today. Tentatively will cover Chapters 3


5 and
possibly Chapter 6. Sample Questions are posted


Project topics are due before spring break (March 7).
Decide on a topic and come talk to me about it. The topic
can be anything of current cosmological interest.


1
st

Quarter observing nights are next Monday and
Tuesday. Forecast isn’t good. Would still like to have a
training session before Monday. Forecast for tonight looks
OK so plan on coming out tonight. Meet at the observatory
around 7:00pm

The Universe according to
Quantum Mechanics


You can’t tell precisely where anything is.


You can’t tell precisely how fast anything is
moving.


Particles act like waves.


Waves act like particles.


Particles can pass through “solid walls”


A very non
-
deterministic universe completely
contrary to Newton’s mechanical universe

According to
the Bohr
model you
cannot tell
where the
electron is,
only what its
energy is.

Heisenberg's Uncertainty Principle says

The Bohr Energy Level Diagram

Electron
energy is
quantized

When an electron changes
energy level it radiates or
absorbs a photon of light

Ionization

If an incoming photon has enough energy it can
completely knock the electron out of the atom

Isotopes
have the
same
atomic
number but
different
mass
number

Radioactive Decay by Alpha
Particle emission

Radioactive decay by Beta
particle emission

Nuclear Fission splits large
nuclei

Nuclear fusion combines small
nuclei

What are protons and neutrons
made of?

If they can decay into something else, they must be
made of something smaller.

Particle
Physics:

The
Particle Menagerie


Bosons

Graviton…spin = 2


mass = 0


charge = 0

Fermions

It gets even worse with baryons

And don’t forget Mesons

The Four Fundamental Forces:
The Strong Nuclear Force

The best thing we have to describe the strong nuclear
force is called quantum chromodynamics or QCD

The Electromagnetic Force

The Weak Nuclear Force

Alpha Decay

Beta Decay

The Gravitational Force

which best describes gravity is Einstein’s General Relativity.
We will go into GR in much more detail later

Newton’s Universal
Gravitation works well for
most situations but the theory

Work & Energy

Energy is a relatively new concepts. Gottfried Leibniz
first proposed something similar to kinetic energy in the
late 1600’s. Thomas Young was the first to use “energy”
in the modern sense in 1807

Gottfried Leibniz


1646
-

1716

Thomas Young


1773
-

1829

Physical Work: the application of a
force over a distance

Potential Energy: the ability to do
work

Each of the four fundamental forces has a potential energy
associated with it. The one we see the most is gravitational
potential energy. Nuclear potential is important in the
interiors of stars and the early universe.

Kinetic Energy: energy of motion

Anything that moves and has mass has kinetic energy: ½ mv
2

Conservation of Energy

Energy can never be created or destroyed.
Only its form can be changed

Thermodynamics

The Zeroth Law of
Thermodynamics

Thermodynamic Equilibrium
means there is no net heat
flow from one object to
another

First Law of Thermodynamics

Basically a statement of the Conservation of Energy

Second Law of Thermodynamics

Any system which
moves heat from a cool
temperature to a warmer
temperature
must

have
some energy input.

Any system which does work by removing heat from a
heat source
must

exhaust some heat

Third Law of Thermodynamics

You can’t get there
from here!

It is impossible to achieve a
temperature of absolute zero

The Laws of Thermodynamics


Zeroth Law: there is a
game
called thermodynamics
and
you’re in it


1
st

Law: you can’t win


2
nd

Law: you can’t break
even


3
rd

Law: you can’t get out of
the game

Result: you may win some in
the short term but in the long
run


YOU LOSE!