newton’s laws of motion and planetary orbits gravity makes the solar system go round
TRANSCRIPT
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Newton’s Laws of Motion and Planetary Orbits
Gravity makes the solar system go round
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Getting ahead of things a bit…using Kepler’s Laws to explore Saturn with
the Cassini spacecraft• http://saturn.jpl.nasa.
gov/video/videodetails/?videoID=85
• http://saturn.jpl.nasa.gov/video/videodetails/?videoID=197
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Newton’s Laws of Motion…vocabulary
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Newton’s Laws of Motion
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The net force is what moves things
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Demonstrations of Newton’s Laws of Motion
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Demonstrations of Newton’s Laws of Motion
What does this have to do with solar system objects? Or astronomy?
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A planet in an orbit around the Sun has its velocity change from one second to another, so it is
accelerating. A force must therefore be acting on it, but what kind of force?
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The orbits of the planets means they are acted on by a force
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Centripetal acceleration and central force…let’s figure out the nature of the
force
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For an object moving on a circular path the acceleration is always towards the center of the circle. So the force must be pointing in that direction, too.
What kind of force could produce that motion?
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For an object moving on a circular path the acceleration is always towards the center of the circle. So the force must be pointing in that direction, too.
What kind of force could produce that motion?
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The nature of Gravity: gravity holds the solar system together
Gravity is an attractive force between two objects because they have mass
M mr
So what does this have to do with the motion of the planets?
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The gravitational force from spherical object
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The application of Newtonian physics to orbital motion
• The solution to F=ma for a planet is an ellipse with the Sun at one focus (Kepler’s 1st Law)
• The semimajor axis and orbital period are related by:
Kepler’s 3rd Law (or is it?) ??????
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The application of Newtonian physics to orbital motion (continued)
Since the force is always in the direction of the center of the
ellipse, the torque is always zero, and angular momentum is
constant
Kepler’s 2nd Law is a consequence
demonstration
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Summary---Newton’s laws of motion, and Newton’s equation for the gravitational force (Newtonian
mechanics) allow us to understand, and calculate with tremendous
precision, the orbits of planets and other objects in the solar system.
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Next Topic: The Moon
The nearest astronomical object, Rosetta Stone of the solar system
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Relative size of the Earth and Moon
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The orbit of the Moon
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The Moon and similar objects