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IB Physics: Relativity
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Gravity
Terms in this set (38)
Frame of Reference
A coordinate system in which measurements of position and time can be made.
Galilean Transformation
Transforming from one inertial frame to another moving at constant velocity.
Inertial Frame of Reference
A frame of reference that is not accelerating but is at rest or moving with a constant velocity for which newton's 1st and 2nd laws hold true.
Special Theory of Relativity
Two postulates:
1) The laws of physics are the same in all inertial reference frames.
2) The speed of light in a vacuum is the same for all inertial observers.
Simultaneity
Two events occurring at different points in space and which are simultaneous for one observer cannot be simultaneous for another observer in a different frame of reference.
Events that are simultaneous for one observer and occur at the same place are simultaneous for all observers.
Light Clock
The time taken for a beam of light to bounce between two perfect, parallel mirrors can be used to measure time.
Proper Time Interval
The time measured by a clock moving with the event being measured, or the time that would be measured if the measurement were taken at rest.
Time Dilation
An effect of relativity in which moving clocks run slow
t = to / [(1 - v2 / c2)^0.05]
Lorentz Factor (γ)
A relativistic factor that varies from approximately 1 at low velocities to approaching infinity near the speed of light
Proper Length
The length of an object measured when at rest relative to the observer.
Length Contraction
A stationary observer will see to points of a moving object contract in the direction of motion.
Twin Paradox
Different observers' measurements of the time taken for a journey at speeds close to the speed of light will not be the same (NOTE: Since one of the twins has to accelerate in the spaceship, this is no longer a symmetrical situation for the twins. The space journeying twin records a shorter time measurement ("ages less."))
Hafele-Keating Experiment
A 1971 test of the predictions of time dilation in which atomic clocks were put in aircraft and flown, east and west, around the world and then compared with clocks that remained fixed in the same location on Earth (NOTE: The clock flying eastward, being the fastest relative to the surface of the Earth, recorded the smallest elapsed time.) (NOTE: The experiment also had to take into account the effects of general relativity since the clocks were at different heights in a gravitational field.)
Rest Mass
The mass of an object as measured in a frame of reference where the object is at rest.
Total energy
Takes into account both the rest mass energy and the kinetic energy of the object.
Equivalence of mass and energy equation
e=mc^2
Why no object can ever attain
the speed of light in a vacuum
Only particles with no rest mass (such as photon) can travel with the speed of light.
As the speed of the object increases, the relativistic mass of the object increases, therefore acceleration will gradually decrease.
Total energy of an accelerated particle
The total energy E, momentum p, and the rest energy E0 (=m0c2) have a relationship E2 = p2c2 + E02.
Muon Decay Experiment
An experiment comparing the number of muons in cosmic rays that reach the Earth's surface without decaying as compared to the number predicted to hit the surface calculated without using relativity theory (NOTE: The results of this experiment give evidence to support the special theory of relativity)
Michelson-Morley Experiment
An experiment comparing the speed of light measured in two perpendicular directions using interference patterns- originally meant to measure the speed of the Earth through the ether - did not produce any observable difference in the speeds gives experimental support for one of the postulates of special relativity
Michelson-Morley Experiment Implications
The ether does not exist and the result is consistent with the constancy of the speed of light.
Gives experimental support for one of the postulates of special relativity.
Pion Decay Experiment
An experiment involving the decay of a fast-moving pion into two gamma ray photons - Indicates that the speed of light in a vacuum is independent of its source
General Theory of Relativity
A more general theory of relativity that takes into account accelerating (non-inertial) reference frames (and the effects of gravity)
Gravitational Mass
The property of an object that determines how much gravitational force it feels when near another object.
Inertial Mass
The property of an object that determines how much it accelerates when a given force is applied to it.
Principle of Equivalence
A frame of reference accelerating in outer space is equivalent to a frame of reference at rest in a gravitational field
Einstein's Closed Elevator "Thought Experiment"
An object dropped inside a closed elevator will accelerate toward the floor - could be explained in one of two ways: either the elevator is far from any planet but accelerating upward or the elevator is at rest on the surface of planet.
Principle of equivalence - bending of light
As light bends in an accelerating frame of reference, light also bends in a gravitational field.
Principle of equivalence - slowing of time
As time slows down in an accelerating frame of reference, time also slows down near a massive body (which naturally has a gravitational field).
Spacetime
A four-dimensional coordinate system which uses time as its fourth dimension and where any event may be described.
(NOTE: Moving objects follow the shortest path between two points in spacetime.)
(NOTE: Gravitational attraction can be explained by the warping of spacetime.)
Black Holes
A region of spacetime with extreme curvature due to the presence of a mass.
Center of a Black Hole (singularity)
The single point to which all mass would collapse.
Surface of a Black Hole (event horizon)
Where the escape speed is equal to c and within this surface, mass has "disappeared" from the universe.
Schwarzschild Radius (RS)
A particular distance from the center of black hole where the escape velocity is equal to the speed of light.
Gravitational Red Shift
A prediction of the general theory relativity in which clocks slow down in a gravitational field.
Eddington Eclipse Measurements
Arthur Eddington's 1919 measurements during the eclipse of the Sun of the apparent change in position of a star - experimental support for the bending of light by a massive object which is a prediction of general relativity.
Gravitational lensing
The phenomenon wherein light bends due to the strong gravitational field of a massive body.
Experiment for gravitational red-shift.
In the atomic clock frequency experiment, two identical atomic clocks in different altitudes (one on the ground and the other on a rocket) registered different rates. The clock at a higher altitude registered a faster rate, thus providing evidence for gravitational red shift.
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