NOVA Biography
The Paper
ON THE ELECTRODYNAMICS
OF MOVING BODIES
SR Univ. of Toronto
C Ship
Length Contraction is not Visible
The Twin Paradox
General Relativity I
General Relativity II
The world is a dangerous place, not because of those who do evil, but because of those who look on and do nothing.
"I have not yet been able to discover the
cause of these properties of gravity from phenomena and
I frame no hypotheses... It is enough that gravity does
really exist and acts according to the laws I have explained,
and that it abundantly serves to account for all the motions
of celestial bodies.
That one body may act upon another at a distance through
a vacuum without the mediation of anything else, by and
through which their action and force may be conveyed from
one another, is to me so great an absurdity that, I believe,
no man who has in philosophic matters a competent faculty
of thinking could ever fall into it."
Isaac Newton
Let's get started
if the guy in the truck tosses the ball at 25 m/s while the truck is traveling at 25 m/s,
how fast is the ball coming toward the guy on the road?
bg - ball with respect to ground
bt - ball with respect to truck
tg - ball with respect to ground
. . .notice the trajectory of the ball to the motionless guy.
Bart the astronaut sees the light beam go straight up to the mirror, bounce off the mirror and come straight down.
Lisa earth girl sees the light beam go at an angle up to the mirror, bounce off the mirror at an angle and come back down.
Which observer sees the light beam take a longer path?
The speed of light has different values to different observers in relative motion.
or
The time and distance have different values for different observers in relative motion.
The Paradox of Special Relativity
Special Relativity
Is time travel possible?
Has time run out on, Einstein?
Did Einstein cheat?
Faster than Light?
GPS, to the rescue!
Concept
Question A
Explain
the evidence for the Theory of Special
Relativity using the muon
experiment.
Is this convincing evidence?
Concept Question
B
Explain how the Michelson-Morley
experiment led to Einstein's two postulates.
It is ironic that Michelson himself wrote in 1899,
"The more important fundamental laws and facts of
physical reality have all been discovered and they are
now so firmly established that the possibility of their
ever being supplanted in consequence of new discoveries
is exceedingly remote .... Our future discoveries must
be looked for in the 6th place of decimals."
Concept Question
C
Example 8 The
Sun Is Losing Mass.
The sun radiates electromagnetic energy at the rate of
3.92x10^26 W.
(a) What is the change in the sun’s mass during
each second that it is radiating energy?
(b) The mass of the sun is 1.99x10^30 kg. What fraction
of the sun’s mass
is lost during a human lifetime of 75 years?
Any change in the energy of a system causes a
change in the mass of the system according to E=mc^2.
It does not matter whether the change in energy is due
to a change in electromagnetic energy, potential energy,
thermal energy, or so on. Although any change in
energy gives rise to a change in mass, in most instances
the change in mass is too small to be detected.
Give a few examples.