i>clicker quiz #14: Moon’s motion The moon’s spin period and orbital period around the Earth are about the same (both equal to about a month). Which of the following statements is FALSE? A. Only one half of the Moon’s surface is sunlit at any given time but all parts of the Moon receive sunlight at one point in time or another B. One half of the Moon is never visible to a person on Earth C. A person on the Moon would see the Earth go through various phases (i.e. different sunlit fractions) at different times and would see the Earth periodically rise and set D. A person on the Moon would see the Earth go through various phases but would not see the Earth periodically rise and set E. The reason for the equality of the Moon’s spin and orbital periods is because it is
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I>clicker quiz #14: Moon ’ s motion The moon ’ s spin period and orbital period around the Earth are about the same (both equal to about a month). Which.
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i>clicker quiz #14: Moon’s motionThe moon’s spin period and orbital period around the Earth are
about the same (both equal to about a month). Which of the following statements is FALSE?
A. Only one half of the Moon’s surface is sunlit at any given time but all parts of the Moon receive sunlight at one point in time or another
B. One half of the Moon is never visible to a person on Earth
C. A person on the Moon would see the Earth go through various phases (i.e. different sunlit fractions) at different times and would see the Earth periodically rise and set
D. A person on the Moon would see the Earth go through various phases but would not see the Earth periodically rise and set
E. The reason for the equality of the Moon’s spin and orbital periods is because it is tidally locked to the Earth
i>clicker quiz #15: Tidal locking
Venus’s spin period and orbital period around the Sun are about the same (analogous situtation to the Moon-Earth system). Which of the following statements is TRUE?
A. We always see the same half of Venus from Earth
B. The same half of Venus always faces the Sun
C. It is not possible to observe phases of Venus from the Earth
D. It is possible to observe phases of Pluto from the Earth
Special Theory of Relativity (STR)
• Speed of light (in vacuum): c = 300,000 km/s
• Constancy of the speed
of light: Michelson &
Morley experiment
• No signal or object can travel faster than c
[The ultimate speed limit!]
Basic Principles
• The speed of light is the same to all observers
• The laws of physics are the same to all observers
Observable Consequences
• Simultaneity is a relative concept
• Length contraction: moving rulers appear to be short
• Time dilation: moving clocks appear to run slow
• The apparent mass (inertia) of an object increases as its speed increases (impossible to accelerate it up to c)
• Equivalence of mass and energy: E = mc2
Special Theory of Relativity (STR)
Special relativistic effects are important when the SPEED of an object is CLOSE TO THE SPEED OF LIGHT: v ≈ c
Simultaneity and time are relative, not absolute
Marion Jones sees A flash before B
Marion Jones sees A and B flash simultaneously
A B
A B
Measuring the length of a moving object:Length Contraction
The apparent (i.e., measured) length of a moving object is shorter than the “true” length (measured
when the object is at rest)
Measuring time on a moving clock:Time Dilation
A moving clock runs slower than its counterpart at rest
Stationary Clock Moving Clock
Which of the following pictures properly depicts the crescent moonin the evening sky shortlyafter sunset?
A. Neither picture #1 nor picture #2
B. Picture #1 does, but picture #2 does not
C. Picture #2 does, but picture #1 does not
D. Both picture #1 and picture #2
i>clicker quiz #16
#1
#2
i>clicker quiz #17Say it’s midday for an astronomer on Jupiter and, at the same
instant, it is midnight for an astronomer on Earth. The sunlit face of the Earth looks like a full circle (i.e., a “full earth’’) to the astronomer on Jupiter. Which of the following statements is TRUE:
• Jupiter, Earth, and the Sun are in a straight line in that order
• Jupiter is visible to the astronomer on Earth at that instant
• Jupiter is not visible to the astronomer on Earth at that instant
• Jupiter, the Sun, and Earth form a right angle
• Earth, Jupiter, and the Sun are in a straight line in that order
Stationary Car
Moving Car
Moving Car
A Thought Experiment:Length Contraction and an Apparent Paradox
The Garage Attendant’s Perspective
Solution: The driver and garage attendant do not agree on the question of whether the two doors were closed simultaneously
Stationary Garage
A Thought Experiment:Length Contraction and an Apparent Paradox
The Driver’s Perspective
Moving GarageMoving Garage
Moving Garage
The scientist in the laboratory witnesses time dilation,while the Uranium atoms “witness” length contraction
A Real Laboratory Experiment:Direct Verification of Time Dilation and Length Contraction
as Predicted by the Special Theory of Relativity
Beam of fast-moving Uranium atoms
Suitably placed
Geiger counter
Nuclear fission of Uranium atoms
A. The Sun and Solar System lie about 1,000 light years from the center of the Milky Way galaxy
B. The carbon, nitrogen, and oxygen present in the Sun and Earth were synthesized in nuclear fusion reactions in the Sun’s core
C. Mature galaxies tend to look more straggly than infant galaxies
D. The subtle ripples in the density of the early Universe from which galaxies formed left imprints that are visible in the Big Bang’s afterglow
i>clicker quiz #18Which one of the following is
TRUE:
i>clicker quiz #19
Which of the following statements is TRUE:
A. Einstein first postulated the constancy of the speed of light in formulating his general theory of relativity
B. The equivalence of mass and energy is best expressed through the formula: E = mc2
C. Gravitational redshift is a feature of the special theory of relativity
D. The fact that gravity is equivalent to an accelerated frame of reference is the basis of the special theory of relativity
General Theory of Relativity (GTR)
Principle of Equivalence
• All objects experience the same motion in a given gravitational field, irrespective of their mass
[Galileo's experiment at the leaning tower of Pisa]
• Gravitational field <===> Accelerated reference frame
• Gravity can be thought of as a distortion of space-time