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Physics Test 4
Terms in this set (69)
Special Theory of relativity
- 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 that 2 observers, in uniform relative motion, perceive time and space differently.
- 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.
It is a term made up of two parts: Space and time.
They are two fundamental assumptions that the theory of special relativity rests on.
What did the first postulate of special relativity state?
- 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?
- 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.
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?
Einstein 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?
E = mc^2
What is the speed of light and why is it such an important concept in physics? What is the formula?
The speed of light is 3.00 x 10^8 m/sec. Nothing travels faster than the speed of light.
Speed of light
It is equal to 3.00 x 10^8 meters per second.
Relativity of simultaneity
It 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.
- It is when moving rulers are shortened in the direction of motion.
- It is when the observable shortening of objects moving at speeds approaching the speed of light.
- 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.
Energy and mass are equivalent and transmutable. (Mass-energy equivalence).
No physical object can travel faster than___________________________________________.
the speed of light in a vacuum. (Maximum speed is finite).
According to this postulate, the speed of the light as observed inside the space ship by that observer must be 3×10^8 m/s and the speed of light observed by the observer on the earth (the light moving diagonally) must ALSO be 3×10^8 m/s.
Shortly 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?
The 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?
Since 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
What is the result of the special theory of relativity?
- It is that no physical object can equal or exceed the speed of light.
- 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.
How is mass and energy related?
The 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?
1) 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?
1) 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).
It is a theory that describes what happens to matter, energy, time, and space at speeds close to the speed of light.
It is the perspective of an observer from which the position and motion of a system can be described.
According to Einstein's special theory of relativity, when compared to an identical clock at rest, a clock moving with constant velocity will run
(c) At the same rate
(d) Alternately fast and slow
The __________________________ states that the laws of physics are the same for all observers moving uniformly
Principle of relativity
An observer traveling with speed 0.5c moves directly toward a beacon emitting photons with speed c in her direction. The observer measure the speed approaching photons to be
(True or False.) To someone moving horizontally at a speed of 0.99c past a vertical meter stick, the stick will appear to be 100 cm long.
A horizontal stretched spring weighs ____________________________ (more than, less than, the same as) an identical spring that is unstretched.
What are the two principles the Theory of relativity is based on?
The first principle: If you have two objects and nothing else then it's not possible to tell which object is moving, and which object is standing still.
The second principle: The speed of light is the same for all observers.
Is it possible to tell that which/an object is moving?
It is not possible to tell which/an object is moving because in the absence of a force, all objects will continue moving in the same direction with the same speed forever.
Why do objects slow down on earth?
It's because of the force from friction and air resistance.
Imagine you were in a spaceship traveling through space and living life, what would happen if the speed of the spaceship was equal to the speed of light?
If the speed of the spaceship was equal to the speed of light, then time inside the ship would stop altogether.
Imagine you were in a spaceship traveling through space and living life, and you were traveling at the speed of light, would you notice? Why?
You would never notice that time for you slowed down or stopped even if you traveled at the speed of light. The reason why you wouldn't notice is because everything is slower by the exact same amount, including the speed of his thoughts, so time for you appears to be flowing normally.
Suppose you are in between two ships moving together, and you fire a laser to the two other ships. What would be your perspective regarding who gets shot first? What would be the outside perspective?
Your perspective: From you perspective, all three ships are standing still, and the two other ships will receive the laser light at the same time.
Outside perspective: The outsider would see the light from both lasers move at the same speed. Therefore, they will see the left ship receive the laser light before the right ship.
The closer a spaceship approaches the speed of light,____________________________
The shorter it becomes.
Since light must be the same speed for all observers even though it is affected by gravity, __________________________________.
This means that gravity must also affect the rate at which time flows.
Gravity is not a force, but a ____________________________
curvature in space-time
What do objects with mass cause?
A curvature in space-time
How do you travel through the view point of special-relativity?
You travel through a combination of space and time. You travel through space-time.
When does time dilation occur?
It occurs ever so slightly for everyday speeds but significantly for speeds approaching the speed of light.
How much energy is required to propel spaceships to relativistic speeds?
You would need billions of times the energy used to put the space shuttles into orbit.
Because of what, time for a person on Earth and time for a person in a high-speed spaceship are not the same?
The practicality of space travel close to the speed of light is..............................
Prohibitive so far.
What happens when a an object moves at a very high speed relative to an observer?
Its measured length in the direction of motion shrinks.
What is the direction that space contracts itself with?
Space contracts in only one direction, the direction of motion.
............................. is equal to 3.00 x 10^8 meters per second.
Speed of light.
............................. is a theory that describes what happens to matter, energy, time, and space speeds close to the speed of light.
The perspective of an observer from which the position and motion of a system can be described is called a(n) .............................
If you were in a smooth-riding train with no windows, could you sense the difference between uniform motion and rest?
Between accelerated motion and rest?
1. b) No
2. a) Yes
A person riding on the roof of a freight-train car fires a gun pointed forward.
(a) Relative to the ground, is the bullet moving faster or slower when the train is moving than when it is standing still?
b) Same speed
(b) Relative to the freight car, is the bullet moving faster or slower when the train is moving than when the train is standing still?
a) faster relative to the freight car.
b) slower relative to the freight car.
c) same speed relative to the freight car.
1. a) Faster
2. c) same speed relative to the freight car.
Which theory predicts that faster-than-light travel is impossible?
The theory that predicts that faster-than-light travel is impossible is special relativity.
What is the major obstacle to traveling faster than light?
The major obstacle to traveling faster than light is the theory of special relativity. The reason why it is an obstacle is being the theory of special relativity states that an object can not be faster than the speed of light.
It is a theory that claims that there are holes in space that connects you to another place in space that is farther away.
It is a theory that could make the space around a spaceship move faster and push it forward.
How is warp drive like a moving sidewalk?
It is like a moving sidewalk because a warp drive could use the space around the "object" and not only make it faster but push it forward.
List the order of the waves from low to high
3) Infrared waves
4) Visible waves
5) Ultra violet
What is the importance of the "wave"?
They travel at the speed of light.
Why is Special Relativity "special"?
a) It's for objects rotating
b) It's only for accelerating objects
c) It's for all cases
d) It's only for objects moving at a constant velocity or rest with the speed of light constant
d) It's only for objects moving at a constant velocity or rest with the speed of light constant
According to Special Relativity, when an observer is moving, what happens to the speed of light?
Light travels at the same speed
We do not usually observe relativistic effects in our daily lives because:
We are moving at speeds much less than c.
What is a light year?
A unit distance
A place in space where all the rules of physics break down.
It's a star that collapse upon itself and the gravity is so strong that time, and space are distorted.
What would happen to the earth if the sun turned into a black hole?
Nothing, it would just keep rotating.
Ignore the rotation of the earth. Which clock ticks more slowly? Hint: More gravity = more time dilation (slower)
a) The one on the top of a mountain.
b) Cannot be determined from the information given.
c) They tick at the same rate.
d) The one at the bottom of that same mountain.
d) The one at the bottom of that same mountain
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