Astronomy 100
Tuesday, Thursday 2:30 - 3:45 pm
Tom Burbine
tburbine@mtholyoke.edu
www.xanga.com/astronomy100
Help Desk
• There is an Astronomy Help Desk in HAS 205. It
will be open from Monday through Thursday
from 7-9 pm.
The purpose of tests
•
•
•
•
So you study the material
So you learn the material better
Test how well you know the material
Decide your grade
The Test
• The average was 71.5% (28.6 out of 40)
• Grades ranged 12 to 39
Zodiac
• The zodiac is an imaginary belt in the heavens
extending approximately 8 degrees on either side
of the Sun's apparent path (the ecliptic), that
includes the apparent paths of the Moon and the
planets Mercury, Venus, Mars, Jupiter, Saturn,
Uranus, and Neptune.
Now there are 13 constellations
in the zodiac
• Why?
• Originally the zodiac was divided into 12 equally
spaced “signs”
• However, some constellations are big, some are
small
• When the astronomers redid the boundaries, a 13th
constellation was added to the zodiac
Long Term Changes
Since most people did not seem
enjoy the test?
Another Homework Assignment
(Due Thursday March 3rd)
•
•
•
•
•
Make up a test question
Multiple Choice
A-E possible answers
1 point for handing it in
1 point for me using it on test
Homework assignments
due next Tuesday
•
•
•
•
Two due next Tuesday (Feb. 22)
One is from this sheet that I am handing out
Two calculations
Worth 1 HW point
2nd HW assignment
due next Tuesday (Feb. 22)
•
•
•
•
•
•
•
•
•
I want you to pick an element
Write its symbol
Is it a solid, metal, or gas?
Atomic Number
Atomic Mass
Its isotopes
What this element is used for?
http://www.webelements.com/
Worth 1 HW point
Matter
• Matter is material
Energy
• Energy is what makes matter move
• In English Units, we use calories to measure
energy
• In science (and in this class), we will use joules to
measure energy
3 basic categories of energy
• Kinetic energy – energy of motion
• Potential energy – energy being stored for
possible conversion into kinetic energy
• Radiative energy – energy carried by light
Kinetic energy
•
•
•
•
Kinetic energy = ½ mv2
m is mass in kg
v is velocity in meters/s
A joule has units of kg-m2/s2
PRS question #1
• How much energy does a 2 kg rock have if it is
thrown at 20 m/s?
• Kinetic energy = ½ mv2
• A) 200 J
• B) 400 J
• C) 40 J
• D) 800 J
Answer
• KE = ½ * 2 * (20) *(20) = 400 joules
Thermal energy
• Temperature – average kinetic energy of particles
• Higher temperature – more kinetic energy,
particles moving faster
• For examples, air molecules around you are
moving at ~500 m/s
Temperature scales
•
•
•
•
•
•
In America, we use Fahrenheit
Water freezes at 32 degrees F
Water boils at 212 degrees F
Everywhere else, they use Celsius
Water freezes at 0 degrees C
Water boils at 100 degrees C
In Science
• Temperature is measured in Kelvin
• Zero Kelvin is absolute zero – nothing moves
• Add 273.15 to the Kelvin temperature to get the
Celsius temperature
• 273.15 Kelvin = 0 degrees Celsius
Gravitational Potential Energy
• Gravitational Potential Energy released as an
object falls depends on its mass, the strength of
gravity, and the distance it falls
• For example, your gravitational potential energy
increases as you go farther up in the air
• This is because you hit the ground at a faster
speed if you jump from a higher distance
Converting Mass to Energy
• What is the most famous formula in the world?
E = mc2
•
•
•
•
m is mass in kilograms
c is speed of light in meters/s
So E is in joules
very small amounts of mass may be converted
into a very large amount of energy and
Who came up with it?
PRS question #2
• How much energy can be produced if you can
convert 10 kg of material in energy?
• E = mc2
• A) 3.0 x 108 J
• B) 3.0 x 1016 J
• C) 9.0 x 1017 J
• D) 9.0 x 1010 J
Answer
•
•
•
•
E = 10 kg * (3 x 108 m/s) * (3 x 108 m/s)
E = 10* (9 x 1016) J
E = 90 x 1016 J
E = 9.0 x 1017 J
Mass-Energy
• So Mass is a form of potential energy
• Where is one place where you see mass converted
into energy?
Atoms
•
•
•
•
•
Atoms are made up of 3 types of particles
Protons – positive charge (+1)
Electrons – negative charge (-1)
Neutrons – neutral charge (no charge)
Protons and Neutrons are found in the nucleus
Elements
• Different elements have different numbers of
protons
• The properties of an atom are a function of the
electrical charge of its nucleus
Charge
• If an atom has the same number of electrons and
protons, it has a neutral charge
• More electrons than protons, negatively charged
• More protons than electrons, positive charged
• Neutrons have neutral charge so don’t affect the
charge of an atom
Definitions
• Atomic Number – Number of protons
• Atomic Mass – Number of protons and neutrons
• U235 – atomic mass
92- atomic number
• Isotopes – Same number of protons but different
numbers of neutrons
First nuclear weapons
• Worked by nuclear fission
• Use Uranium-235
• If a free neutron runs into a U-235 nucleus, the
nucleus will absorb the neutron without
hesitation, become unstable and split immediately
• The energy released by a single fission is due to
the fact that the fission products and the neutrons,
together, weigh less than the original U-235 atom
Atoms make up molecules
•
•
•
•
H2O
CO2
CH4
Atoms made up with 2 or more different atoms
are called compounds
Questions?