# PHYS 183 Lecture Notes - Lecture 8: Celsius, Liquid Air, Big Bang

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29 Jan 2013
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PHYS 183 The Milky Way Inside and Out Tracy Webb Winter 2013
Lecture 8: January 23rd, 2013
conservation of momentum
o momentum = mass x velocity
o total momentum of an object cannot change unless a net force acts upon them
o interacting objects exchange momentum through equal and opposite forces
o momentum is transferred, not speed
o two pool balls, one has m = 0, other has m = m x v; after the collision other has m = m x v and
original has m = 0
conservation of angular momentum
o angular momentum = mass x velocity x radius (distance to the sun)
o angular momentum of an object cannot change unless an external twisting force acts on it
(torque)
o earth experiences no twisting forces as it moves around the sun rotation & orbit will
continue indefinitely
o earth changes velocity (speed) depending on how close it is to the sun
o explains why objects rotate faster as they shrink in radius when you spin in figure skating
you spin faster if your arms are pulled in
conservation of energy
o kinetic energy motion
earth has kinetic energy in its orbit around the sun
energy we see coming from lamps, computers, sun
o potential energy stored energy
gas, food energy that will be converted into another form of energy
o energy can change type but cannot be destroyed
o thermal energy collective kinetic energy of many particles (in a rock, air or water)
particles move more in higher temperatures and less in lower temperatures
related to temperature, but not the same
depends on both temperature & density
air in oven is 400F and boiling water is 212F, but water in the pot contains more
thermal energy because of its much higher density as a liquid air in oven is a gas so
it is less dense
o temperature is the average kinetic energy of many particles in a substance
temperature scales
o absolute zero: 0K, -273.15C, -459.67F
o water freezes: 273.15K, 0C, 32F
o water boils: 373.15K, 100C, 212F
Kelvin is the Celsius scale but shifted 273 degrees, Fahrenheit doesn’t convert well
the sun is almost 6000 K
gravitational potential energy
o on earth this depends on:
object’s mass (m) more massive an object is, the more gpe it will have
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