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GRAVITY
Falling Objects
A Universal Law
The Tides
Discovering Neptune
Weightlessness?
Curved Space-time
The problem of Mercury
Bending Starlight
Heavy things go slow
Global Positioning System
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Falling Objects
Galileo claimed to have discovered that heavy and
light objects fall at the same rate, by dropping
things from the leaning tower of Pisa.
Actually Galileo never performed that experiment.
If he had, air resistance would have skewed the
results. The real reason that heavy and light
objects fall at the same rate was demonstrated by
Galileo using theoretical arguments.
We can break a heavy rock into two lighter pieces
and stick it back together. If lighter objects
fall slower, than the rock on the right must fall
slower than the rock on the left. But, this is
absurd because they are the same rock.
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A Universal Law
Sir Issac Newton had a wild idea. He
hypothesized that every object in the universe
pulls on every other object, even if the objects
do not touch.
F G Mm/R2
All objects attract each other with a force
directly proportional to their masses, and
inversely proportional to the square of the
distance between them.
Newton admitted that he could not explain why
gravity works, but at least he could describe how
it works.
To learn more about Newton, click below
http//scienceworld.wolfram.com/biography/Newton.h
tml
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The Tides
With his Universal Law of Gravity, Newton was
able to explain the tides. The ocean in
region A is pulled strongly toward the moon. The
ocean in region C is pulled toward the moon less
strongly because it is further away. The rest of
the Earth at B is pulled with a strength more
than C but less than A.
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Discovering Neptune
The Universal Law of Gravitation made it possible
to calculate the orbits of all the planets and
moons in the solar system. However, the observed
orbit of Uranus did not match the theory.
Might the Universal Law of Gravitation be wrong?
Or maybe another planet pulls on Uranus and
changes its orbit.
In 1846 two scientists, Adams and Le Verrier,
independently predicted the existence of the
planet Neptune using pencil and paper
calculations. When astronomer Johann Galle
pointed his telescope where Le Verrier had
suggested, he saw the planet Neptune!
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http//www.nasm.si.edu/ceps/etp/discovery/disc_pla
nets.html
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Weightlessness?
Contrary to popular belief, there is strong
gravity in outer space especially in Earth
orbit. But, we have all seen pictures of
astronauts floating around as if they are
weightless. How can this be?
Remember Galileos discovery from the first
slide? All objects fall at the same rate
regardless of their size. This means that the
space shuttle and the astronauts are falling at
the same rate. So there is no respective motion
between them.
From inside the shuttle it is almost impossible
to detect gravity.
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Curved Space-time
Albert Einstein proposed a radically new way of
thinking about gravity. Time is the fourth
dimension. The other three dimensions are space.
Space and time are part of the same fabric.
Mass causes space-time to stretch. In the region
of a large mass, time slows down and space
stretches out.
As we move forward in time, we follow a curved
path through space!
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The problem of Mercury
The orbit of Mercury around the sun does not obey
Newtons Law of Gravitation. Many scientists
expected to find another planet called Vulcan in
the neighborhood of Mercury, just as Adams and Le
Verrier had found the planet Neptune in the
neighborhood of Uranus. But, no planet Vulcan
was ever found.
Using his new theory of curved space-time.
Einstein was able to correctly calculate the
orbit of Mercury.
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Bending Starlight
Light has no mass. Therefore, according to
Newtons theory light should not be affected by
gravity.
Einsteins theory predicted that light would
follow a curved path through space near massive
bodies, just like normal objects.
In 1919, Eddington observed that the field of
visible stars is distorted near a solar eclipse.
Thus light is affected by gravity.
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Heavy things go slow
Einsteins theory says that time goes slower near
massive objects and under strong gravities. That
means that our clocks, and everything else here
on Earth are being slowed down by gravity.
Even our heartbeats, and the processes of our
brains are slowed down by gravity.
The effect of time dilation is very small on
Earth, but it has been measured by a variety of
experiments.
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GPS
Does all this weird space-time bending stuff have
any application to real life?
Yes, as a matter of fact it does. The Global
Positioning System (GPS) is the primary means of
navigation for many of todays vehicles. The GPS
system is so accurate it can be used to guide
airplanes toward the runway in dense fog. You
can even buy a handheld GPS device to keep track
of your location. The Global Positioning
System uses satellites in orbit to determine
locations here on Earth. In order to minimize
error. The GPS system uses Einsteins theory,
and compensates for the time dilation due to the
Earths Gravity.
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