Transcript PHYSICS 51: Introduction

PHYSICS 50: Lecture 11.1
RICHARD CRAIG
Homework #11
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Chapter 12
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We will skip 12.8
12.3, 12.13, 12.23, 12.54, 12.55
Due Tuesday April 22
Today
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Force of Gravity
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Acceleration due to gravity
Gravitational Potential energy
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Examples
Escape velocity
Circular Orbits
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Examples
Newton’s Law of Gravitation
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There is a force of attraction between
any two masses
F = Gm1m2/R2
G is a universal constant
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G = 6.67 x 10-11Nm2/kg2
Newton’s Law of Gravitation
Examples
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Me and you
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Me and earth
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Three particles
Calculate gravitational variables
To add forces due to multiple masses you must add vectors
climb upward)
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Gravity (and hence, weight) decreases as altitude rises.
Things that effect your
“weight”
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Altitude
Latitude
“Local” variations in rocks
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Barometric pressure
densities below sea level
• Just as it’s interesting to
remember that all
gravitational forces are
calculated from the center of
the planet, it’s interesting to
follow the density as one
proceeds from crust to
mantle to core.
• “Want to get away”?
Consider Example 12.4 to
calculate gravity on Mars.
Gravitational potential energy
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Objects changing their distance from earth are also
changing their potential energy with respect to earth.
Escape Velocity
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If an object has enough kinetic energy to overcome
the gravitational potential energy it can escape from
the gravitational pull
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1/2 mv2 > GmM/R
Satellite motion
Consider satellite orbits
Circular Orbit Examples
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Low Earth Orbit (LEO)
Geosynchronous orbit
Moon