Chapter 12 - UC Santa Barbara...2010/09/12 · Title video slide Author BCP User Created Date...

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley

PowerPoint® Lectures for

University Physics, Twelfth Edition

– Hugh D. Young and Roger A. Freedman

Lectures by James Pazun

Chapter 12

Gravitation


Goals for Chapter 12

• To study Newton’s Law of Gravitation

• To consider gravitational force, weight, and

gravitational energy

• To compare and understand the orbits of satellites

and celestial objects

• To explore the existence and nature of black holes

(beyond science fiction)


Introduction

• Looking at the picture of Saturn,

we see a very organized ring

around the planet. Why do the

particles arrange themselves in

such orderly fashion?

• From Copernicus and Galileo to

Hubble and NASA, centuries of

scientists have struggled to

characterize gravitation and

celestial motion.


Newton’s Law of Gravitation

• The gravitational force is always attractive and depends on both the masses of the bodies involved and their separations.


Henry Cavendish determines G

• Gravitational forces were relative until 1798 when Henry Cavendish made the sensitive measurement to determine a numerical value for the constant G.

• G ~ 6.6742 x 10-11 N-m2/Kg2


Calculate gravitational variables

• Example 12.1 leads us through an example of the gravitational force between two masses.

• Example 12.2 leads us to an acceleration that will result from a gravitational force.

• Example 12.3 reminds us that gravitational forces are vectors and are all active in a physical situation. See Figure 12.5 below.


Weight (skip Weight Watchers, just climb upward)

• Gravity (and hence, weight) decreases as altitude rises.


Gravitational force changes 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

• Objects changing their distance from earth are also

changing their potential energy with respect to earth.


Jules Verne had no way to know…

• To escape from the earth, an object must have escape

velocity (not a small number).

• Follow Example 12.5 and Figure 12.12.


Satellite motion


Consider satellite orbits

• Several images of things in orbit to consider are shown below.

• Follow Example 12.6.


Kepler’s laws for planetary motion

• Each planet moves in an

eliptical orbit with the

sun at one focus.

• A line connecting the sun

to a given planet sweeps

out equal areas in equal

times.

• The periods of the

planets are proportional

to the 3/2 powers of the

major axis lengths in

their orbits.


Orbital questions

• Consider Conceptual Example 12.7 about orbital speeds.

• Refer to Example 12.8 about Keppler’s Third Law.

• Example 12.9 examines the orbit of Halley’s Comet.


Spherical mass distributions

• Newton delayed the publication of his gravitational work

until he was certain he could treat each planetary object

from its center.

• Consider Example 12.10 and Figure 12.25.


Spherical mass distributions II


A visit to a black hole

• Refer to Example 12.11 and Figures 12.29 and 12.30.

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Chapter 12 - UC Santa Barbara...2010/09/12 · Title video slide Author BCP User Created Date...

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