Transcript Slide 1

1) Fg or Gravitational force or FORCE of gravity (STRENGTH of gravity) depends on 2
factors: a) MASSES of the 2 bodies
and
b) DISTANCE between the 2 bodies
2) Gravitational force is STRONGER when masses are bigger OR when distance between 2
bodies are CLOSER
Gravity: every object in the universe attracts every other object with a force that depends on the
MASSES of the 2 objects and the DISTANCES between the 2 objects
Inertia: RESISTANCE to change in motion – an object going straight resists change unless a force is
applied to it.
2 MAIN factors that effect gravity: 1) mass of objects ; 2) distance between masses
Fg
=
Force of Gravity (or strength of GRAVITY between 2 masses) Fg =
(M1x M2)
d2
G
FORCE of GRAVITY is stronger between 2 bodies when
1) masses are bigger
2) DISTANCES are closer
(For example : MOON and EARTH have stronger gravitational attraction to each other than the SUN and the earth
because the distance between the MOON and the EARTH is smaller than distance between the SUN and the Earth
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What were contributions/observations/laws made by:
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Galileo (leave 10 lines)
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Tyco Brahe (leave 10 lines)
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Johann Kepler: Laws of motion (leave 10 lines)
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Isaac Newton: Laws of gravity (leave 10 lines)
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Albert Einstein: Theory of Relativity (leave half a page)
http://astro.unl.edu/naap/lps/animations/lps.swf
Same face toward earth (pink); phases -- where is earth relative to sun
always 1/2 lit;
Gravity on EARTH
Gravity on Earth……
affects how fast falling objects fall
(they fall at rate of 32 ft/second2 or 9.8 m/second2
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/physicallaws.htm
GRAVITY of Earth
affects your weight
WEIGHT is pull or force of gravity
on your mass
weight = Fg = your mass x g
g is a CONSTANT 
gravitational
acceleration or gravitational constant
on earth: g= 9.8 m/second2)
or 32.2 feet/second 2
g has different values on other planets
g on
GRAVITY
combined with INERTIA
helps keep
1) the moon revolving around the Earth…
2) Earth revolving around SUN…
and 3) all the planets revolving around the SUN…..
Without gravity, the planets would all
fly off in a straight line
into space……
Force GRAVITY and force of INERTIA –
MOON held in orbit by Earth’s GRAVITY
INERTIA causes moon to move straight; GRAVITY pulls it in toward EARTH
In FIGURE of EARTH and MOON
Inertia (RED arrow)
Moon is moving in a straight line.
FORCE of INERTIA resists change of
straight line movement.
GRAVITY (GREEN arrow) –
is FORCE of GRAVITY (attraction)
between EARTH and MOON
FORCE of GRAVITY applied to object
moving in straight line overcomes
FORCE of INERTIA and effectively
tugs moon inwardly toward earth
from its STRAIGHT path.
Moon and Earth revolving around each
other and a center of mass (+)
http://www.sailingissues.com/navcourse6.html
Gravity and inertia cause
all planets to revolve around SUN
Intertia
gravity
Gravity between the Earth, the
MOON and the SUN causes
1) TIDAL bulges
2) Thicker crust on side of moon facing EARTH
3) Wobble in Earth’s orbit
1) MOON’s gravitational effect on earth is
TIDAL bulges (TIDES!!!)
2) EARTH’s gravitational effect on the moon is
- Thicker moon crust on FAR side of moon
that always faces AWAY from earth (same side
of moon faces earth – we have NEVER seen
back side of moon except from pictures of a
satellite that passed behind the moon)
http://astro.unl.edu/naap/lps/animations/lps.swf
Same face toward earth (pink); phases -- where is earth relative to sun
always 1/2 lit;
3) Slight Wobble in Earth’s path due to pull of
moon on earth in FULL and NEW moon
positions
http://www.valdosta.edu/~cbarnbau/astro_demos/tides/neap_sp.ht
ml
-http://www.mmscrusaders.com/newscirocks/tides/tideanim.htm
2 main types:
SPRING
NEAP
Tides: 2 high and 2 low every 24 hours
Tides rise 50 minutes later each day
http://home.hiwaay.net/~krcool/Astro/moon/moontides/
http://highered.mcgraw-hill.com/sites/dl/free/0072482621/59233/5_5.htm
lows 2 times per 24 hours
Earth moving into TIDAL bulges 2 times per 24hr and TIDAL
Moon’s pull on tidal bulge slows Earth’s rotation
Earth pulls moon ahead in its orbit
Net result is
earth wobbles a bit in its orbit as moon orbits around it;
Earth’s pole now points to Polaris (north star) but pole is being shifted; in 13,000 years
VEGA will be our NEW North star
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Figure 15.4 Solar System Formation The
condensation theory of planet formation (not
drawn to scale; Pluto is not shown in part e).
SWIRLING cloud of gas and dust collapse ;
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(a) The solar nebula after it has contracted and
flattened to form a spinning disk (Figure 15.1b). The
large blob in the center will become the Sun.
Smaller blobs in the outer regions may become
jovian planets.
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(b) Dust grains act as condensation nuclei, forming
clumps of matter that collide, stick together, and
grow into moon-sized planetesimals as a result of
GRAVITY pulling the matter together. The
composition of the grains depends on location
within the nebula –
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(c) Strong winds from the still-forming Sun will
soon expel the nebular gas. By this time, some large
planetesimals in the outer solar system have
already begun to accrete gas from the nebula.
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(d) With the gas ejected, planetesimals continue to
collide and grow. The gas giant planets are already
formed.
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(e) Over the course of a hundred million years or so,
planetesimals are accreted or ejected, leaving a few
large planets that travel in roughly circular orbits.
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Example: gravity attraction
between SUN and EARTH
m1 = earth mass
m2 = sun’s mass = 1000 m1
r = Distance = 1 AU
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F = g m1 1000m1
r2
FORCE sun-earth _________
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Gravity attraction between EARTH
and moon
m1 = earth mass
m2 = moon’s mass = .25 m1
R = 0.01 AU
F = g m1 .25m1
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r2
FORCE earth-moon
__________
Facts about the moon
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http://www.classzone.com/books/earth_science/terc/content/visualizations/es2501/es2501page01.cfm?c
hapter_no=visualization
GRAVITY pulls together the pieces
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http://astro.unl.edu/naap/lps/animations/lps.swf
Same face toward earth (pink); phases -- where is earth relative to sun
always 1/2 lit;
Gravity:
Inertia:
every object in the universe attracts every other object with a force that depends on
the MASSES of the 2 objects and the DISTANCES between the 2 objects
RESISTANCE to change in motion – an object going straight resists change unless a force is
applied to it.
2 MAIN factors that effect gravity: 1) mass of objects ; 2) distance between masses
Fg
=
Force of Gravity (or strength of GRAVITY between 2 masses)
Fg
=
G (M1x2M2)
d
FORCE of GRAVITY is stronger between 2 bodies when
1) masses are bigger
2) DISTANCES are closer
(For example : MOON and EARTH have stronger gravitational attraction to each other than the SUN and the earth
because the distance between the MOON and the EARTH is smaller than distance between the SUN and the Earth
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What were contributions/observations/laws made by:
SUN at center theory
PTOLEMY (time period
)– GEOCENTRIC (earth at center of universe) theory
COPERNICUS (time period
) - HELIOCENTRIC (sun at center of universe theory)
• Tyco Brahe (leave 10 lines)
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Galileo (leave 10 lines)
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Johann Kepler: Laws of motion (leave 10 lines)
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Isaac Newton: Laws of gravity (leave 10 lines)
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Albert Einstein: Theory of Relativity (leave half a page)
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WHEN MASS of objects INCREASED, what is result? REVISED
FORCE of GRAVITY is INCREASED/stronger
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-- means bigger either of the masses, stronger the
gravitational force
OR as either of the masses is increased, the Force of
gravity is increased by the PRODUCT
Force of Fg INCREASED by
m1 x m2
1Fg
m1 x 2m1 =
1 x 2 or
2Fg
2m1 x 2m1
2 x 2 or 4 Fg
m1 x 3m1
1 x 3 or 3 Fg
3m1 x 3m1
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WHEN MASS of objects INCREASED, what is result?
FORCE of GRAVITY is DECREASED /not as strong
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-- as distance is increased between masses, the force of
gravity is weakened by factor of 1/r2
Force of G DECREASED by
R=1r m1----m2
Fg
R= 2r m1-----------m2
1/(2r)2 = ¼ of Fg
R = 3r m1----------------m3 1/(3r)2 1/9 of Fg
R = 4r
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R =5r
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WHEN MASS of objects INCREASED, what is result?
FORCE of GRAVITY is INCREASED/stronger
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1) means bigger either of the masses, stronger the
gravitational force
OR as either of the masses is increased, the Force of
gravity is increased by the PRODUCT
Force of G INCREASED by
m1 x m2
1G
m1 x 2m1 =
2G
3G
2m1 x 2m1
m1 x 3m1
4G
3m1 x 3m1
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4 m1 x 2m1
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8 m1 x 10m1
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WHEN MASS of objects INCREASED, what is result?
FORCE of GRAVITY is DECREASED /not as strong
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2) as distance is increased between masses, the force
of gravity is weakened by factor of 1/r2
Force of G DECREASED by
R=1 m1----m2
1
R= 2 m1-----------m2
1/(2)2 = ¼
R = 3 m1----------------m3
1/(3)2 1/9
R=4
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R =5
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B
C
D
INCREASE in MASS
A. When 1 mass doubles, force (F) is increased by _______
B. when both masses double, force of gravity is increased by _____________
D. When 1 mass stay the same, but the second mass increase by 3, force of gravity is increased
by _____________
INCREASE in DISTANCE
A. When distance doubled (radius is 2r), force of gravity (F) is decreased by 1/r2 or 1/22 or 1/4
Our weight – the effect of GRAVITY of
mass (EARTH) on another mass (ours)
Weight
Jumps
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The gravitational attraction between the Earth and the
moon is strongest on the side of the Earth that
happens to be facing the moon, simply because it is
closer. This attraction causes the water on this “near
side” of Earth to be pulled toward the moon. As
gravitational force acts to draw the water closer to the
moon, inertia attempts to keep the water in place. But
the gravitational force exceeds it and the water is
pulled toward the moon, causing a “bulge” of water on
the near side toward the moon (Ross, D.A., 1995).
On the opposite side of the Earth, or the “far side,” the
gravitational attraction of the moon is less because it
is farther away. Here, inertia exceeds the gravitational
force, and the water tries to keep going in a straight
line, moving away from the Earth, also forming a bulge
(Ross, D.A., 1995).
In this way the combination of gravity and inertia
create two bulges of water. One forms where the Earth
and moon are closest, and the other forms where they
are furthest apart. Over the rest of the globe gravity
and inertia are in relative balance. Because water is
fluid, the two bulges stay aligned with the moon as the
Earth rotates (Ross, D.A., 1995).
The sun also plays a major role, affecting the size and
position of the two tidal bulges. The interaction of the
forces generated by the moon and the sun can be
quite complex. As this is an introduction to the subject
of tides and water levels we will focus most of our
attention on the effects of the stronger celestial
influence, the moon.
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Inertia, acts to counterbalance gravity. It
is the tendency of moving objects to
continue moving in a straight line.
Together, gravity and inertia are
responsible for the creation of two
major tidal bulges on the Earth (Ross,
D.A., 1995).
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Gravitation, or gravity, is a natural phenomenon by which physical bodies attract
with a force proportional to their mass. In everyday life, gravitation is most familiar
as the agent that gives weight to objects with mass and causes them to fall to the
ground when dropped.
Gravitation causes dispersed matter to coalesce (come together), and coalesced
matter to remain intact, thus accounting for the existence of the Earth, the Sun,
and most of the macroscopic objects in the universe.
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Gravitation is responsible for keeping the Earth and the other planets in their
orbits around the Sun; for keeping the Moon in its orbit around the Earth;
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GRAVITY of the Earth-moon-sun system is responsible for the formation of tides;
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GRAVITY is responsible for natural convection, by which fluid flow occurs under
the influence of a density gradient and gravity;
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GRAVITY is responsible for heating the interiors of forming stars and planets to
very high temperatures;
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What keeps a planet in orbit around the sun, or the moon around the earth, or
other moons around their planets are forces of 1) GRAVITY and 2) inertia.
Inertia: resistance to change in motion