Kinetic Energy

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Kinetic Energy
This is the energy of motion For those
interested, kinetic energy can be written as ½
mv2
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Temperature and Thermal Energy
Temperature is tough to describe Its really a
measure of average kinetic energy
Dots and arrows describe moving particles
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Temperature Scales
The zeropoints for Celsius are easy does
anyone know what 0 F corresponds to?
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Temperature and Density
Just as important as the temperature is the
density. Ill put my hand in a 500 F oven But I
sure as hell wont put my hand in 210 F water!
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Phase Transitions
Phase transitions occur when matter goes through
different states solid, liquid, gas,
plasma Energy also plays a part in phase
transition Energy is needed to melt ice or
vaporize water. But energy is released when
water vapor condenses. Phase transitions play an
important role in the early universe.
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Rest Energy or Mass Energy
This is the whole E mc2 thing This is the
source of energy in nuclear weapons. Stars also
tap this energy source through fusion.
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Conservation of Energy
The total energy in a closed system is
conserved. However, as weve just seen, energy
can be hidden (stored potential energy) in lots
of ways.
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Conservation of Angular Momentum
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Gravitation

• Every mass attracts every other mass through the
  force of gravity
• The strength of gravity is proportional to the
  product (multiply) of the masses involved.
• The strength of gravity decreases with the
  square of the distance between the objects.

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More on Gravitation

• Forcegravity G M1 M2 / d2
• Where G, the gravitational constant, is equal to
  6.67 x 10-11 m3 kg-1 s-2
• check the units
• Everyone understand how I wrote the units?
• Gravity is an inverse-square law
• Double the distance and the force is ¼
• Triple the distance and the force is 1/9th

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Inverse-Square Law
A
Assume them all to be the same mass, the force
between the objects in B will be ¼ the force
between the objects in A. And C will be 1/9th
the force compared to A
1 km
B
2 km
C
3 km
What if I change the masses? Remember, 3rd Law ?
same force on each object.
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Orbital Energy
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Escape Velocity
This is the energy or corresponding velocity
needed to overcome the potential energy of
gravity. That is, how fast do I have to throw it
so that it doesnt fall back to Earth
11 km/s for Earth
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Bound and Unbound Orbits
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Atmospheric Drag
Theres still wind/air resistance in space. Its
just very small and insignificant if youre far
away from the atmosphere. Also asteroids and
dust This drag causes a loss of energy that
will modify orbits of artificial satellites.
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Planetary Encounters
We use this slingshot effect when planning
satellite trajectories.
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Tides
Black arrows ?Force due to Moon
High Tide
Low Tide
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Moons Gravity Earths Gravity
If an area of water moves 1 towards the high
tide region, it pushes the adjacent area that way
too so its not that water is flowing ¼ the way
around the Earth
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Todays/Tomorrows Tides
Notice anything about the moon rise/set times?
Credit tbone.biol.sc.edu/tide/tideshow.cgi
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Tidal Forces

• These types of forces are found in many places
• Near black holes, tidal forces are extremely
  strong
• Our galaxy is ripping apart a nearby dwarf galaxy

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Which Exerts More Gravitational Force on Earth
Moon or Sun (average)
FsunGMSunMEarth/DistanceSun2 3.5 x 1021
Newtons FmoonGMMoonMEarth/DistanceMoon2 2.0
x 1020 Newtons Ratio is all we really want, plus
its easier RatioSun/Moon (MSun/MMoon)/(DSun/DM
oon)2
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What is the Force Due to the Moon on the Near and
Far Sides of Earth?
FnearGMMoonMEarth/ (DistanceMoon
radiusEarth)2 2.07 x 1020 N FfarGMMoonMEart
h/ (DistanceMoon radiusEarth)2 1.93 x 1020
N Difference 1.4 x 1019 N
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What is the Force Due to the Sun on the Near and
Far Sides of Earth?
FnearGMSunMEarth/ (DistanceSun
radiusEarth)2 3.5749 x 1022 N FfarGMSunMEar
th/ (DistanceSun radiusEarth)2 3.5743 x 1022
N Difference 6 x 1018 N versus 1.4 x 1019 N
for the Moon
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Spring Tides and Neap Tides
Click Here
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Synchronous Rotation of the Moon
Do we always see the same side of the moon?
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