Transcript Chapter 5 The Mechanical Universe

Chapter 5
The Mechanical Universe
Chapter 5
• Newton
– Not only does this guy come up with
three laws of motion. The guy figures
out that objects exert gravitational
forces on one another.
– He probably came up with the idea after
he denied a colleage grant money.
– Folklore has it that while Newton was
sitting underneath an apple tree. The
idea of gravity came to him when an
apple struck him on the head.
Chapter 5
• Newton’s Law of Gravity
– Between any 2 objects there is an
attractive force that is
proportional to the product of the
two objects’ masses and
proportional to the inverse of the
square of the distance between
them.
Chapter 5
• Gravitational Force between the
Earth and the Moon.
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–
–
–
Mass of Earth is 6.0 x 1024 kg
Mass of Moon is 7.4 x 1022 kg
Orbital radius is 384 x 106 m
When I plug the above numbers
into the gravity equation I get a
Fgravity = 1.96 x 1020 N
Chapter 5
• Gravitational Force between the
Sun and the Earth.
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–
–
–
Mass of Earth is 6.0 x 1024 kg
Mass of Sun is 1.99 x 1030 kg
Orbital radius is 149.6 x 109 m
When I plug the above numbers
into the gravity equation I get a
Fgravity = 3.5 x 1022 N
Chapter 5
• Gravitational Force between
two people weighing 135 lbs
separated by a meter.
– Mass of person is 61.3 kg
– Orbital radius is 1 m
– When I plug the above numbers into the
gravity equation I get a Fgravity = 2.5 x
10-7 N
– This number is not detectable or easily
measurable and is why the gravitational
attraction between people goes
unnoticed.
Chapter 5
• Gravity is partly responsible for
the evolution of the universe.
– Roughly 5 billion years ago, our
solar system was a cold cloud of
gas and dust in space.
– Part of this gas cloud had a region
where matter was highly
concentrated.
– This region of highly
concentrated matter began to
gravitationally attract more and
more mass to it.
Chapter 5
• Stellar Evolution cont’d
– As the process continued, that
region of highly concentrated
mass begins to increase in size
and temperature.
– The temperature increase is due to
gas molecules colliding at greater
and greater speeds.
Chapter 5
• Stellar Evolution cont’d
– While the region of highly
concentrated matter was heating
up and increasing in size it also
began to spin causing the outer
regions to flatten out.
– A star comes alive when the
temperature in the region of
highly concentrated matter
reaches a million degrees, nuclear
fusion can take place.
Chapter 5
• Stellar Evolution cont’d
– Nuclear fusion is a type of nuclear
reaction where two elements
collide together and form a new
element in addition to releasing
energy.
– In stars the hydrogen atoms
collide and form helium as well as
energy being released.
– The nuclear fusion process creates
a lot of pressure.
Chapter 5
• Stellar Evolution cont’d
– The outward pressure of the gas
of hydrogen and helium atoms
balances the inward pull of
gravity.
– Now at some point there is no
more hydrogen atoms to convert
to helium and gravity will begin
to dominate until the region of
high matter concentration shrinks.
Chapter 5
• Stellar Evolution cont’d
– That region of high mass
concentration will get squeezed
into a solid, densely packed
atoms.
– This stellar corpse is hot, solid,
and small and is called a white
dwarf. It will glow brightly for a
while and then slowly dim like a
dying ember.
Chapter 5
• Stellar Evolution cont’d
– Notes: