Transcript Gravity & Motion

Gravity & Motion
Astronomy
Kepler’s Laws of Motion
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First- Planets move in
elliptical orbits around Sun
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Foci- Two fixed points in an
ellipse
Major axis- Maximum
diameter of ellipse
Semimajor axis- Half of major
axis
Eccentricity- Ratio of distance
between foci and major axis
Perihelion- Planet is nearest
Sun
Aphelion- Planet farthest from
Sun
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Second- Planets move like there is
an imaginary line connected to the
Sun
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Third- Squares of sidereal periods of
planets is proportional to cubes of
semi-major axes
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Sidereal period- Time for planet to
complete one orbit around Sun
Galileo
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Mathematician by choice
Experimented with gravity by dropping objects
Air resistance determines speed
Once an object is in motion, it will remain in
motion unless acted upon
René Descartes
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Believed that all changes
in motion due to
“corpuscles”
Inertial motion- Motion
when there are no
unbalanced forces acting
on object
Early planetary motion
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Aristotle & Ptolemyplanetary bodies
located on
crystalline spheres
Robert Hooke- knew
about Sun’s force on
planets
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Central force- Force
acting on a center of
motion
Gravity
• What is gravity?
Sir Isaac Newton
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Brilliant man with
numerous
discoveries, but
needed a little push
Wrote Principia
about planetary
orbits and gravity
Newton’s three
laws:
Law of Inertia
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An object at rest remains at rest unless
acted upon by unbalanced force
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Inertia- Resistance to changes in motion
Velocity- Speed and direction of an object
Acceleration- rate velocity changes with time
Mass- Measure of inertia of a body
Momentum- Mass multiplied by velocity
(direction & magnitude)
Law of Force
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When an unbalanced
force acts upon an
object, it produces a
change in momentum
in the direction in
which the force acts
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Force- A push or pull
Law of Action & Reaction
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When one body
exerts a equal and
opposite force on
another body, the
second body also
exerts a force on
the first.
Orbital Speed and Energy
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Kinetic energy
Gravitational potential
energy
Tides
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Distortions in shape resulting from tidal
forces
Tidal forces- differences in gravity in an
object being attracted to another
Solid Earth (Terrestrial) tides- Distortion
due to moon & Sun
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22 inches at equator (5.9 in due to Sun)
Generate currents in conducting fluid within
Earth [magnetic field]
Ocean tides- Tidal acceleration causes
vertical and horizontal movement
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Spring- Unusually high or low
Neap- Weak tides
The day gravity reversed itself…