CH 7 Albert Einstein and the Theory of Relativity

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CH 7 Albert Einstein and the Theory of Relativity

• Frames of reference
• No matter the frame of reference, the laws of
  nature are the same

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Homework- CH 7
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The Speed of Light, Michelson-Morley
The Michelson-Morley Experiment The 19th century
view was that light was a wave. There was great
interest in determining how the speed of light
varied with the velocity of the light's source.
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The Michelson-Morley Experiment could not detect
changes in the speed of light no matter which
direction it was propagated. Light seemed to have
a constant velocity.
reflected waves would be
out
of phase if the Earth's rotation

affected the speed of light Earth's rotation
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Light has wave-particle duality.

• Light has wave-particle duality.
• Experiments show light to act like a particle.
• We call these photons or photons of light.
• Experiments also show the wave nature of light.

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The photoelectric effect.
The photoelectric effect shows the particle
nature of light. In the photoelectric effect, a
beam of light knocks electrons out of atoms
generating an electric current.
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Two-Slit Experiment The Atomic lab
http//www.colorado.edu/physics/2000/index.pl
Go to Table of context Classic two slit experiment
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Albert Einstein
Finally, in 1905, Albert Einstein suggested that
since everyone who measured the velocity of light
in space got the same value, no matter how either
the observer or the source of the light was
moving, it must be a characteristic of the
universe that Light has a constant velocity in
space.
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Relativity

• Frames of Reference
• Special Relativity
• Objects that move but do not accelerate
• General Relativity
• Objects that accelerate

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Descriptions in Different Reference Frames

• Coins path appears different depending on your
  frame of reference

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Albert Einstein, moving away from a clock tower,
imagined how different observers might view the
passage of time. If Einstein were traveling at
the speed of light, for example, the clock would
appear to him to have stopped, even though his
own pocket watch would still be ticking.
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Time dilation, A light clock

• A flashing light and a mirror. A light pulse
  bounces off the mirror and returns to trigger the
  next pulse.
• stationary clock and
• a moving clock.
• Light from the moving clock must travel farther,
  and so it appears to a stationary observer to
  tick more slowly.

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A person in the rocket turns on a light for ten
seconds (for them). It takes 1 second before
a observer on the ground sees the light go onand
5 seconds for them to see it go off. The person
on the ground therefore sees the light for 14 sec
(10 sec - 1 sec 5 sec) 14 sec.
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A spaceship in motion appears to contract in
length, L, along the direction of motion. The
height, H, and width of the ship do not appear to
change, however.
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Newton
The motion of rolling balls A ball travels in
uniform motion unless acted upon by a force
motion occurs along curved paths in a flat
universe. .
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Einstein
The motion of rolling balls A balls mass
distorts the universe it moves in a straight
line across a curved surface.
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Einsteins curved space and time
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Relativity

• Moving clocks run slower.
• Moving objects shrink in the direction they are
  moving.
• Mass increases with velocity.

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The equations
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An example

• A 1.0000000000000 meter object moving a Length at
  90 mph (40.2 m/s)

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An example

• Length dilation at 80 speed of light(2.4 x 108
  m/s). Lrest 1 meter

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Relativity

• Relativity may be hard to comprehend but it has
  been verified in the laboratory.