Review

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Review
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Chapters 9-14
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Classical Relativity
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A Reference System
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Reference system the set of objects that are
not moving relative to each other and that can be
therefore used as the basis for detecting and
describing motion.
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Galileo asked if observers could decide whose
description was correct. He concluded that they
couldnt. In fact, each observers description
was correct!
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Galilean Principle of Relativity
The laws of physics are the same for all inertial
reference systems.
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Questions
1. Alice in Wonderland begins with Alice falling
down a deep, deep rabbit hole. As she falls, she
notices that the hole is lined with shelves and
grabs a jar of orange marmalade. She is afraid to
drop the jar for it might hit somebody on the
head. What would really happen to the jar if
Alice had dropped it? Describe its motion from
Alices reference system and from the reference
system of someone sitting on the shelf.
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You wake up in a windowless room on a train,
which rides along particularly smooth tracks.
Imagine that you have a collection of objects and
measuring devices in your room. What experiment
could you do to determine whether the train is
stopped at the train station or moving
horizontally at a constant velocity?
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Assume that you are riding in a windowless train
on perfectly smooth tracks. Imagine that you have
a collection of objects and measuring devices in
the train. What experiment could you do to
determine whether the train is moving
horizontally at a constant velocity or is
speeding up?
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Accelerating Reference System
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Forces that arise in accelerating reference
systems are called inertial forces. Another
common label for these forces is fictitious
forces.
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Special Theory of Relativity
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Postulates of the Special Theory of Relativity
The idea of an absolute frame of reference was
gone with the idea of stationary ether.
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First Postulate
All laws of nature are the same in all uniformly
moving frames of reference.
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Second Postulate
The speed of light in the free space has the same
measured value for all observers, regardless of
the motion of the source or the motion of the
observer that is, the speed of light is a
constant.
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Simultaneity
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Two events that are simultaneous in one frame of
reference need not be simultaneous in a frame of
reference moving relative to the first frame.
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This non simultaneity of events in one frame that
are simultaneous in another is a purely
relativistic effect a consequence of light
always having the same speed for all observers.
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Two side-by side observers at rest relative to
each other share the same reference frame. Both
would agree on measurements of space and time
intervals between given events, so we say they
share the same realm of spacetime.
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Time Dilation
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Lorentz Factor, g
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If you are moving in a spaceship at a high speed
relative to the Earth, would you notice a
difference in your pulse rate? In the pulse rate
of people back on the Earth? Will observers A
and B agree on measurements of time if A moves at
half the speed of light relative to B? If both A
and B move together at half the speed of light
relative to the Earth?
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Space travelers on the way to colonize a planet
orbiting a distant star decide to cook a
three-minute-egg. Would a clock on Earth record
the cooking time as less than, equal to or
greater than 3 minutes? Why?
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In an experiment to measure the lifetime of muons
moving through the laboratory, scientists
obtained an average value of 8 microseconds
before a muon decayed into an electron and two
neutrinos. If the muons were at rest in the
laboratory, would they have a longer, a shorter,
or the same average life? Why?
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Length Contraction
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Peter volunteers to serve on the first mission to
visit Alpha Centauri. Even traveling of 80 of
the speed of light, the round-trip will take a
minimum of 10 years. When Peter returns from the
trip, how will his biological age compare with
that of his twin brother Paul, who will remain on
Earth?
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Is it physically possible for a 30-year-old
college professor to be a natural parent of
40-year-old student? Is it possible for length
contraction to occur without time dilation?
Explain. Suppose the meter stick zips by you at
a speed only slightly less than the speed of
light. If you measure the length of the meter
stick as it goes by, would you determine it to be
longer than, shorter than, or equal to 1 meter
long? Why?
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General Theory of Relativity
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The principle of equivalence states that
observations made in an accelerated reference
system are indistinguishable from observations
made in a Newtonian gravitational field.
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An astronaut awakes in her closed capsule, which
actually sits on the moon. Can she tell whether
her weight is the result of gravitation or
acceleration motion? Explain. You wake up at
night in your berth on a train to find yourself
pulled to one side of the train. You naturally
assume that the train is rounding a curve but you
are puzzled that you dont hear any sounds of
motion. Offer another possible explanation that
involves only gravity, not acceleration in your
frame of reference.
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Bending of Light by Gravity
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According to the principle of equivalence, if
light is deflected by acceleration, it must be
deflected by gravity.
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Gravity and Time
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According to Einsteins general theory of
relativity, gravitation causes time to slow down.
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The Atomic Hypothesis
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• The ideal gas model accounts very well for the
  behavior of gases at standard temperature and
  pressure. Would the ideal gas model begin to fail
  for very large pressures or for very small
  pressures? Explain your answer.
• A cube and a spherical ball are made of the same
  material and have the same mass. Which exerts the
  larger pressure on the floor?

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• You may apply enough force to the head of a
  pushpin to push it into a plaster wall with you
  thumb. However, it is not a good idea to try to
  do this with a needle. Use the concept of
  pressure to explain the difference between these
  two situations.
• If you screw the cup of empty plastic drinking
  bottle on tightly while walking in the mountains,
  why are the sides of the bottle caved in when you
  return to the valley?

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• Your right rear tire has to support a weight of
  3000 N. Normally, the contact area of your tire
  with the road is 200 square cm. If the pressure
  in your tire is suddenly reduced from 32 pounds
  per square inch to 16 pounds per square inch,
  what must be the new contact area to support the
  car?
• Use the microscopic model of gas to explain why
  the pressure in a tire increases as you add more
  air.

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• If the average speed of a perfume molecule is 500
  meters per second, why does it take several
  minutes before you smell the perfume from a
  bottle opened across the room?
• 2. What happens to the average speed of the
  molecules of a gas as it is heated?

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States of Matter
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The fraction of object submerged is given by the
ration of the objects density to that of the
fluid.
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Pascals Principle
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A change in pressure at any point in an enclosed
fluid at rest is transmitted undiminished to all
points in the fluid.
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• What shape would you expect a drop of water to
  take if it were suspended in the air in the space
  shuttle?
• If you fill a glass with water so the water is
  level with the top of the glass, you can
  carefully drop several pennies into the glass
  without spilling any water. How do you explain
  this?
• Are you ears going to hurt more swimming 12 feet
  down in your swimming pool or 12 feet down in the
  middle of Lake Superior? Explain.

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• Fresh water has a density of 1000 kg per cubic
  meter at 4C and 998 kg per cubic meter at 20C. In
  which temperature water would you feel the
  greater pressure at the depth of 10 meters? Why?
• Salt water is denser than fresh water. Would a
  scuba diver have to go deeper in salt water or in
  fresh water to reach the same pressure? Why?
• Use Archimedes principle to explain why an empty
  freighter sits higher in the water than a loaded
  one.

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Barometers
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• Is there a buoyant force acting on you in the
  air? If there is, why you are not buoyed up with
  this force?
• How does buoyancy change as helium-filled balloon
  ascends?

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Bernoullis Principle
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Where the speed of a fluid increases, internal
pressure in the fluid decreases.
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• A scuba diver achieves neutral buoyancy by
  adjusting the volume of air in her buoyancy
  compensator vest (BCD) so that the buoyant force
  equals her weight. If she then kicks her fins and
  swims down an additional 20 feet, will the net
  force now be upward, zero or downward? Explain.

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The Nature of Heat
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Zeroth Law of Thermodynamics
If two systems are in thermal equilibrium with a
third system, then they are in thermal
equilibrium with each other.
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First Law of Thermodynamics
The increase in internal energy of a system is
equal to the heat added plus the work done on the
system.
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Third Law of Thermodynamics
Absolute zero ma be approached but experimentally
but can never be reached.
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Specific Heat
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The amount of heat it takes to increase the
temperature of an object by 10C is known as heat
capacity of the object.
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Change of State
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Latent Heat
If a material changes phase from solid to liquid,
or from liquid to gas, a certain amount of energy
is involved in its change of phase.
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• If you make the mistake of removing ice cubes
  from the freezer with wet hands, the ice cubes
  will stick to your hands. Why does the water on
  your hands freeze rather than the ice cube melt?
• In northern climates drivers often encounter
  signs that read BRIDGE FREEZES BEFORE ROADWAY.
  Why does this occur?