Systems of Units English = uck! metric: meter-kilogram

Systems of Units
English = uck!
metric: meter-kilogram-seconds [mks, SI]
centimeter-grams-seconds
Natural (speed of light = 1)
Legos?
Elementary Particles
mass
charge
symbol
proton
“heavy”
+
+
electron
“light”
-
e-
neutron
“heavy”
(proton +
electron)
none
n
Atoms
e-
nucleus
+ + n+
+ n n
n+ n
Not real! Just a mental picture or model!
(Bohr Model of Atom)
e-
element
• smallest unit of a substance that still has the
properties of that substance (i.e., periodic table)
• Determined by number of protons
isotope
• same elements with different numbers of neutrons
ion
• same element with unequal number of protons and
electrons
(BEWARE: Physicists often use colloquial names
concerning ions and isotopes!!!)
Examples
e-
e-
+
+
n
Hydrogen
(H)
Deutrium
(H)
(Tritium has 2 neutrons)
More Examples
e++
n n
++
n n
Helium
(He)
Alpha particle
(He+2)
e-
More Examples
e-
e+ ++
n nn
+++
n nn
e-
e-
eLithium
(Li)
Lithium
(Li+1)
Common Elements and Symbols
H=hydrogen
He=helium
Li=lithium
C=carbon
O= [atomic] oxygen
Na=sodium
Fe=iron
Pb=lead
Si=Silicon
Molecules
A stable collection of atoms is called a molecule
(I sometimes call them a “bulk object”)
H2O = Water
O2 = [Molecular] Oxygen
CO2= Carbon Dioxide
CH4 = Methane
What Moves Legos?
Things with mass generate gravity (g)
(Likewise, gravity can affect things with mass)
Things with charge (protons and electrons)
generate electric fields (E)
(Likewise, electric fields can affect things with charge)
“Spooky action at a distance”
Things with charge (protons and electrons)
that are moving (also called a current)
generate magnetic fields (B)
(Magnetic fields can affect things with
charge that are moving/currents)
We often get lazy and, instead of saying
“electric field and magnetic field,”
we just say
“electromagnetic field.”
Gravity and electromagnetic fields are 2 of the 4 forces in
nature and are the 2 that we will encounter in this class.
[The strong force and the weak force are the others]
ALL FIELDS ARE ASSOCIATED WITH THE
TRANSFER OF ENERGY
Energy
A fictitious quantity that, generated by the
aforementioned fields, allows for objects to move.
MKS system uses Joule [J] as unit of energy
(you might be more familiar with calorie?)
A Joule per second [J/s] is a Watt [W]
When atoms or molecules “happens across” energy,
[usually] 1 of 2 things can happen:
1) they wiggle-jiggle more [we classify the amount of
“wiggling-jiggling” by the quantity of temperature]
2) the energy, if it is a) in the form of a special type of
electromagnetic field and b) of a specific frequency,
can be absorbed
1. Temperature
“How much the atoms and molecules of a
substance wiggle and jiggle”
In MKS system, we use the Celsius scale [oC]
or
the Kelvin scale [K]
K = oC + 273.15

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