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24 Cards in this Set

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  • Back
Aristotelian View of Motion
Absolute rest is a natural state for earth and absolute motion is ascribed to all heavenly bodies. This is because if the earth were in a state of motion, an object thrown vertically upward on the surface would not return to its initial position.
Galileo's challenge
Galileo pointed out that the absolute character of rest and motion and the earth's state of absolute rest couldn't be established by the Aristotelian method. How do we know when we are at rest or moving?
Frames of Reference
A Galilean pilot would stay that a boat in isolation is at rest.If the pilot is on shore, then the boat is in motion. The distinctions between the sates of rest and motion recedes and the notion of motion or the Galelian type is ambiguous apart from a reference point.A Cartesian system allows for
Uniform Motion
It is constant velocity which is an object moving at a constant velocity traversing equal distances in equal intervals of time in a straight line.

The effects of uniform motion are indistinguishable from the effects of nonmotion. Hence it is a relative concept.
distance traveled / time elapsed
Internal Observer
An observer who has no physical way of determining whether he is at rest or in uniform motion.
Law of inertia
An object at rest remains at rest and an object in uniform motion persists in uniform motion in the absence of external disturbances.
Inertial frame of reference
Any reference system in which the law of inertia holds valid. All inertia frames of reference are equivalent.
Galilean principle of relativity
This principle requires that all laws of mechanics be formulated so as to be all inertial frames of reference.
19th century physics
The science of electricity and magnetism, electromagnetivity
James Clerk Maxwell
1860s - Discovered that the then-known laws of electricity and magnetism could be summarized in a set of mathematical equations
Electromagnetic waves
The speed of these waves in empty space (3 X 10^8 m/s) was equivalent to the speed of light in a vacuum (also empty space). Thus electromagnetic waves and light are one and the same thing.
Maxwell versus Galileo and Newton
Maxwell's equations aren't consistent with Galilean principle of relativity. Maxwell's laws could distinguish a state of motion from a state of rest. Hence Maxwell could prove that there was an absolute frame of reference and concept of absolute motion.
Waves and mediums
All familiar waves such as sound and water waves require a medium cause a wave is nothing more than a disturbance in a medium.

Ex. A pebble tossed to the senterof a pond creates waves that disturb the smoothness of the water.
Hypothetical substance for "empty space"
A true vacuum can not represent true emptiness. Thus, empty space can be clothed with a physical substance to pervade all space. Hence the idea of electromagnetic ether as an absolute frame of reference
Electromagnetic ether
The ether has to be frictionless, transparent, incompressible and of uniform density because the velocity of light would be different if it wasn't uniformly dense, if it wasn't transparent then the stars would be invisible. It also surrounds the universe.
Ether as an absolute frame of reference
Electromagnetic ether solved the problem of electromagnetic waves traveling without a physical medium.
The Experimental setup of the Michelson-Morley experiment
It seeks to determine the absolute velocity of the earth with respect to ether. Since the earth revolves around the sun, then the earth does move in the sea of ether.
The Analogy of a Boat and a River
The Michelson-Morley experiment is like the analogy of a boat and a river in that one can measure the speed of a river current through measuring the speed of the motor boat.
Moving up current
Trip against the current: The boat's speed with respect to the current is c and the current flows at a velocity of v in reference to the bank, then the boat's apparent speed to an observer on the bank is (c - v) Cause the velocity of the current will slow down the speed of the boat when it's moving up against the current.
t(up) = L / (c - v)
Moving down current
The boat would be moving at a higher velocity according to the observer on the bank because it can go in the direction of the current. Thus
t(down) = L (c+v)
Total time round trip
t(up) + t(down) = 2L / c(1 - v2/c2)
A trip across the current
The boat must be directed diagonally into the current in order to travel straight across the river and not be carried downstream. The boat crossing the current is u relative to the bank. The speed relative to the water is c. So the speed of the boat can be understood as
c2 = u2 + v2 or equation as u=c square root of 1 - v2/c2
The experimental result
They expected that the time of transit of rthe two mutually perpendicular light beams would be different and so the measurement of the time difference would bring the same velocity of the ether current with respect to the earth. However no matter how much they moved the apparatus, the light beams always arrived together. So is it that the velocity of the ether was zero?