Transcript Unit 5B Universal Gravitation

Inquiry
Imagine what would it have been like to
see a solar eclipse in ancient times?
 What would those people have
wondered?
 Describe a conversation between two
young people viewing an eclipse in the
year 500 B.C.E.

The Sun-Eating Dragon
Sun Gods
Ra and Surya
Stonehenge
Solar Eclipse
Solar Eclipse
May 10 1994
Solar Eclipses
visible in USA
• August 21, 2017
• April 8, 2024**
• **How old will you be?
UNIVERSAL GRAVITATION
FROM ARISTOTLE TO EINSTEIN
ARISTOTLE
384-322 BC
• Nature is made up of 4 elements plus the
quintessence
•
•
•
•
•
Air
Earth
Fire
Water
Quintessence-celestial realm
• Taught that objects have natural tendency to
be at rest at the center of the Earth.
PTOLEMY
87-170 AD
• Wrote the Almagest which detailed a
Universe that was highly complex
• Wrote of a geocentric Universe which
consisted of known planets, moon, sun, and
the stars.
• Used ideas of epicycles, deferents, and
equaints to describe the orbits in his model
COPERNICUS
1473-1543
• Polish priest that taught of a heliocentric
Universe
• Explained retrograde motion of Mars, and
motion of the inferior (inner) planets
• Strongly opposed by Catholic church which
supported Ptolemaic system of the Universe
Brahe/Kepler
• Tycho Brahe (1546-1601)
– Danish astronomer that tirelessly observed the
heavens, and collected immense amounts of
data on their motions.
• Johannes Kepler (1571-1630)
– 1st model utilized 5 regular solids
– Hired as mathematical assistant to Brahe
– Developed model of solar system now known
as Kepler’s 3 Laws
Kepler’s 1st Law of
Planetary Motion
•
Planets move in ellipses with the Sun
at one focus
How to Make an Ellipse
Kepler’s 2nd Law of
Planetary Motion
• Planets sweep out equal areas in equal
times.
Note: Orbit shown is highly eccentric
Planets Greatest
Speed
Planets Least
Speed
Kepler’s 3rd Law of
Planetary Motion
• The Ratio of the Squares of their Orbital
Periods are equal to the Ratio of the Cubes
of the Mean Radii of their Orbits.
(Tmars)2
(Rmars
)3
= Constant
(Tmars)2
(Tvenus)2
=
(Rmars)3
(Rvenus)3
GALILEO
1564-1642
• Constructed the first telescope that was used
to view the moon and planets
• Believed in and taught the Copernican
heliocentric Universe
• Was sentenced to house arrest by the Pope
for espousing that view
• May be considered the first physicist and
the creator of the scientific method
ISAAC NEWTON
1643-1727
• Inspired while at Woolesthorpe during the
black plague epidemic
• Mythological apple fell on his head while
viewing the moon
• Kept ideas in desk drawer
for 20 years
UNIVERSAL GRAVITATION
• The force of gravity is directly
proportional to the product of the two
masses, and inversely proportional to
the square of the distance between their
centers.
• The law is universal to all masses and
works throughout the Universe
Universal Law of Gravitation
m1m2
Fg  2
r
HENRY CAVENDISH
1731-1810
• Determined experimentally the value of
Newton’s Universal Gravitational constant
–G = 6.67 x
-11
10
N·
• Cavendish indirectly measured
the mass of the earth
2
2
m /kg
UNIVERSAL LAW OF
GRAVITATION
Gm1m2
F
2
r
ALBERT EINSTEIN
1879-1955
• Space as we know it really consists of
4 dimensions combined, which he coined
space-time.
• The gravitational effect on objects
(planets, stars, etc.) is caused by a
large mass warping space-time.
Space-time
Planet or Star
THE WARPING OF SPACE-TIME
BLACK HOLES- A star so dense that it
infinitely warps space-time to a point, and
consequently even light
cannot escape.
Stephen Hawking
Acceleration due to gravity
GM e
g
2
Re
Gravity Fields
g
g
g
Centripetal Force as Gravity
2
GM e m
mv

2
Re
Re
Orbital Velocity
GMe
v orbital 
Re
Escape Velocity
vesc
2GM e

Re
To go where no man has gone…