Astronomy 100 Tuesday, Thursday 2:30 3:45 pm Tom Burbine tburbinemtholyoke.edu www.xanga.comastronom

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Astronomy 100Tuesday, Thursday 230 - 345
pmTom Burbinetburbine_at_mtholyoke.eduwww.xanga.
com/astronomy100
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Help Desk

• There is an Astronomy Help Desk in HAS 205.  It
  will be open from Monday through Thursday from
  7-9 pm.

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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

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The Test

• The average was 71.5 (28.6 out of 40)
• Grades ranged 12 to 39

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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.

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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

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Long Term Changes
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Since most people did not seem enjoy the test?
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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

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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

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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

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Matter

• Matter is material

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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

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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

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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

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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

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Answer

• KE ½ 2 (20) (20) 400 joules

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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

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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

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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

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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

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Converting Mass to Energy

• What is the most famous formula in the world?

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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

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Who came up with it?
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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

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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

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Mass-Energy

• So Mass is a form of potential energy
• Where is one place where you see mass converted
  into energy?

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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

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Elements

• Different elements have different numbers of
  protons
• The properties of an atom are a function of the
  electrical charge of its nucleus

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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 dont affect the
  charge of an atom

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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

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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

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Atoms make up molecules

• H2O
• CO2
• CH4
• Atoms made up with 2 or more different atoms are
  called compounds

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Questions?