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Physics Finals Questions and Answers 100% Correct
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Exam of 40 pages for the course Relativity at Relativity (Physics Finals)
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Physics FinalsSpecial Theory of relativity - answer- Developed by Einstein
- It is a theory created by Einstein that describes how time is affected by motion in
space at constant velocity, and how mass and energy are related.
- It describes those 2 observers, in uniform relative motion, perceive time and space
differently.
Time Dilation - answer- It was an idea proposed by Einstein that stated that time can be
stretched depending on the motion between the observer and the events being
observed.
- It occurs whenever we move through space, we to some degree alter our rate of
moving into the future.
- It is also known as "the stretching of time."
- A slowing of time in accordance with the theory of relativity that occurs in a system in
motion relative to an outside observer and that becomes apparent especially as the
speed of the system approaches that of light — called also time dilatation.
Space-time - answer1) It is a term made up of two parts: Space and time.
2) In order for "c" to remain constant, the ratio of space to time HAS to remain the
SAME
3) Distance in space = changes, then time changes too
4) 1 observer's measurements of space + time differ from the measurements of another
observer in another spacetime
5) Farther you travel in space close to the speed of light, the longer the second is. Once
sped of light is reached time stops
What does Time Dilation = - answer....... = immense speed = greater gravity
Speed of Light - answer1) Represented as "c" (root = celeritas)
2) 300,000,000 m/s
3) 3 X 108 m/s
4) NOTHING moves faster than the speed of light
5) Travels of packets of energy called photons (not mass but acts like mass)
Postulates - answerThey are two fundamental assumptions that the theory of special
relativity rests on.
What did the first postulate of special relativity state? - answer- It states that all the laws
on nature are the same in all uniformly moving frames of reference.
,- It can assume our inability to detect a state of uniform motion.
What did the second postulate of special relativity state? - answer- It states that the
speed of light in empty space will always have the same value regardless of the motion
of the source or the motion of the observer.
- It assumes that the speed of light is constant at 300,000 km/s
- The ratio of space to time for light is the same for all who measure it.
What was the reasoning behind Albert Einstein's ideas? - answerEinstein reasoned that
all motion is relative and all frames of reference are unpredictable. An object cannot
measure its speed relative to empty space, but only relative to other objects.
According to Einstein's formula, what is the relationship between mass, energy, and the
speed of light? - answerE = mc^2
What is the speed of light and why is it such an important concept in physics? What is
the formula? - answerThe speed of light is 3.00 x 10^8 m/sec. Nothing travels faster
than the speed of light.
Speed of light - answerIt is equal to 3.00 x 10^8 meters per second.
Relativity of simultaneity - answerIt is when two events that occurred simultaneously for
one observer were not simultaneous for another observer if the two observers had
relative motion to each other.
Length contraction - answer1) It is when moving rulers are shortened in the direction of
motion.
2) It is when the observable shortening of objects moving at speeds approaching the
speed of light.
3) Objects are measured to be shorter in the direction that they are moving with respect
to a stationary observer.
Ex: How is it possible that the two observers measure the same rocket ship to be two
different lengths? When the rocket ship is at rest on the earth, the on-ship meter stick
and the off-ship meter stick are exactly the same but when the rocket ship flies past the
earth at significant fraction of the speed of light, the on-ship meter stick as seen by the
on earth observer has shrunk. When the observer on ship says the ship is still 15 m
long, the observer on earth says, "Nope, your meter stick has shrunk and so has your
ship. The ship now measures 7.5 m long using my meter stick." The on-ship meter stick
shrinks by the same percentage that the ship shrinks.
E=mc^2 - answerEnergy and mass are equivalent and transmutable. (Mass-energy
equivalence).
Twin Paradox - answerShortly after Einstein proposed the special theory of relativity, an
apparent paradox was pointed out. This paradox involved a pair of twins, one of whom
traveled away from the earth and returned at very high speeds. The other twin remained
,at home on earth. Since one twin was traveling at very high speed, time for him was
running slower than for the twin who remained on earth. Thus the traveling twin would
return home younger than the twin who remained on earth.
The paradox comes about when each twin thinks that their frame of reference was at
rest and the other twin's frame of reference was moving at high speed. Therefore, each
twin would find the other one to be younger. The resolution lies in the fact that the
traveling twin must accelerate at the beginning and end of the trip and this acceleration
guarantees that this twin is traveling and his clock is actually running slower. The
traveling twin will return home younger than his twin brother.
What was the clock test in 1971? What was the outcome? - answerThe clock test was
when one clock was sent around the world in high speed jet planes while the matched
clock remained at rest. When the traveling clock was returned and placed next to the
other clock, the traveling clock showed that less time had passed.
What are the three basic mechanical quantities? - answer1) Length
2) Time
3) Mass.
Relativistic Mass - answerSince length and time have been shown to be relative (their
value depends on the reference frame from which they are measured), it might be
expected that mass is also relative. Einstein showed that the mass of an object
increases as its speed increases according to the formula
M = mo
. ---------
√1 - v^2
. -----
. c^2
What is the result of the special theory of relativity? - answer1) It is that no physical
object can equal or exceed the speed of light.
2) It essentially explains how to interpret motion between different inertial frames of
reference, that is, places that are moving at constant speeds relative to each other.
Mass + Energy - answer1) Piece of matter even at rest + not interacting w/ anything =
has "energy of being"/ rest energy
2) Einstein = concluded that it takes energy to make mass + that energy = released if
mass disappears
3) Amount of energy (E) = related to amount of mass (m)
Ex: E = mc^3
- E = (.001kg)(3 x 10^8)^2
- E = (.001kg)(9 x 10^16)
- E = 9E13 Joules
, What does this mean: Motion is relative - answer1) The place from which motion =
observed + measured is the frame of reference
- An object may have different velocities relative to different frames of reference
2) To measure the speed of an object, we 1st choose a frame of reference + pretend
that we are in that frame of reference standing still
- Measure the speed w/ which the object moves relative to us = relative to frame of
reference
How is mass and energy related? - answerThe idea is not that mass and energy can be
mathematically related but that they two are, in fact, simply different forms of the same
thing. Each may be converted into the other and the conversion factor is the speed of
light squared.
What are the two postulates special relativity is based on? - answer1) The laws of
physics are the same for all observers within their own inertial reference frame.
2) The speed of light in a vacuum is the same for all observers regardless of their
relative motion or the motion of the source of the light.
What are some examples that explain the theory of special relativity? - answer1) Two
events that occurred simultaneously for one observer were not simultaneous for another
observer if the two observers had relative motion to each other. (Relativity of
simultaneity).
2) Clocks in a moving frame of reference tick more slowly than an observer's
"stationary" clock. (Time dilation).
3) Objects are measured to be shorter in the direction that they are moving with respect
to a stationary observer. (Length contraction).
4) The mass of a moving object will be greater as measured by an observer at rest.
5) E=mc2, energy and mass are equivalent and transmutable. (Mass-energy
equivalence).
6) No physical object can travel faster than the speed of light in a vacuum. (Maximum
speed is finite).
Special relativity - answerIt is a theory that describes what happens to matter, energy,
time, and space at speeds close to the speed of light.
Reference frame - answerIt is the perspective of an observer from which the position
and motion of a system can be described.
What does "Space" have to do with the theory of Special Relativity? - answerWhen
moving through space, you are moving through time too
Earth → Sun = 8.3 minutes
What are the four dimensions of our world? - answer1) Length
2) Width
2) Height
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