In Class:
Question to Ponder
If the Sun is so much more massive than the Earth, and the strength of
the gravitational pull depends on mass, why aren't we pulled off the
Earth and toward the Sun?
Review: The World Up There is the Same as the World Down Here
- Newton's work on gravity shows that stuff in the celestial environment
plays by the same rules as stuff in the terrestrial environment.
- If the heavens are really the same stuff as what's down here, then
we should be able to understand the heavens by extension of what we
know down here.
- Unfortunately, it's hard to get to the celestial environment, so
traditional lab techniques (i.e., analyzing a sample) are "out of
reach."
- We're stuck with studying the light that comes from these
objects.
The Nature of Light: Newton's Answer
- Newton reasons that the space between the planets is empty
(otherwise, the friction would slow down the planets, and they'd
spiral into the Sun, which would be bad).
- Since waves must travel through a medium, Newton decides that
light must be particulate.
- With his prism experiment, he shows that white light is made up
of all of the colors of the rainbow.
- With his particulate (or "corpuscular," as Newton would've called
it) model, he decides that there are particles of many different
colors of light, and that when they all enter your eye at the same
time, you see white light.
- Newton's theory of light holds sway for more than 100 years.
The Nature of Light: Young's Answer
- Thomas Young tries his two-slit experiment:
- Instead of seeing two dots projected onto the back of a darkened
box, he sees a pattern of bright and dark spots.
- This pattern is what one would expect from the interference of
waves emanating from the two slits.
- Young (and everyone around him) concludes that light must be a
wave.
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