Download Chapter 20

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Orrery wikipedia, lookup

Definition of planet wikipedia, lookup

History of Solar System formation and evolution hypotheses wikipedia, lookup

Planets beyond Neptune wikipedia, lookup

Equivalence principle wikipedia, lookup

Newton's laws of motion wikipedia, lookup

Modified Newtonian dynamics wikipedia, lookup

Aquarius (constellation) wikipedia, lookup

Astronomical unit wikipedia, lookup

Timeline of astronomy wikipedia, lookup

Tropical year wikipedia, lookup

Extraterrestrial life wikipedia, lookup

Dialogue Concerning the Two Chief World Systems wikipedia, lookup

Formation and evolution of the Solar System wikipedia, lookup

Rare Earth hypothesis wikipedia, lookup

Geocentric model wikipedia, lookup

History of astronomy wikipedia, lookup

Copernican heliocentrism wikipedia, lookup

Kepler (spacecraft) wikipedia, lookup

First observation of gravitational waves wikipedia, lookup

Satellite system (astronomy) wikipedia, lookup

Lunar theory wikipedia, lookup

Transcript
1. An industrial flywheel has a greater
rotational inertia when most of its mass is
 (a) nearest the axis.
 (b) nearest the rim.
 (c) uniformly spread out as in a disk.

2. A ring and a disk both of the same
mass, initially at rest, roll down a hill
together. The one to reach the bottom first
 (a) is the disk.
 (b) is the ring.
 (c) both reach the bottom at the same time.

3. Put a pipe over the end of a wrench
when trying to turn a stubborn nut on a bolt,
to effectively make the wrench handle twice
as long, you'll multiply the torque by
 (a) two.
 (b) four.
 (c) eight.

Chapter 9
Gravity
Newton’s law of gravitation





Attractive force between
all masses
Proportional to product of
the masses
Inversely proportional to
separation distance
squared
Explains why g=9.8m/s2
Provides centripetal force
for orbital motion
Newton’s Law of Universal
Gravitation

From Kepler's 3rd Law, Newton deduced
inverse square law of attraction.
Gm1m 2
F
2
d

G=6.67  10-11 N m2/kg2
Gravity Questions

Did the Moon exert a gravitational force on the
Apollo astronauts?

What kind of objects can exert a gravitational
force on other objects?

The constant G is a rather small number. What
kind of objects can exert strong gravitational
forces?
Gravity Questions

If the distance between two objects in space is
doubled, then what happens to the gravitational
force between them?

What is the distance is tripled?
…is quadrupled?




What if the mass of one of the object is doubled?
…tripled?
…quadrupled?
Weight and Weightlessness

Weight
» the force due to gravity on an object
» Weight = Mass  Acceleration of Gravity
»W=mg

“Weightlessness” - a conditions wherein
gravitational pull appears to be lacking
– Examples:
» Astronauts
» Falling in an Elevator
» Skydiving
» Underwater
Ocean Tides

The Moon is primarily responsible for ocean
tides on Earth.

The Sun contributes to tides also.

What are spring tides and neap tides?
Spring Tides
Full Moon
Earth
New Moon
Sun
Neap Tides
First Quarter
Earth
Last Quarter
Sun
BLACK HOLES
Let’s observe a star that is shrinking but
whose mass is remaining the same.
What happens to the force acting on an
indestructible mass at the surface of the
star?
SFA
F
F
F
m
m
1
2
m1m2
F

G
2
G
Remember that the force between
R
2
the
two
masses
is
given
by
R
G
G
m1m2
R2
R
m1m2
R2
R
R
R
F
G
m1m2
R2
BLACK HOLES
If a massive star shrinks enough so that the
escape velocity is equal to or greater than the
speed of light, then it has become a black hole.
Light cannot escape from a black hole.
Einstein’s Theory of Gravitation

Einstein perceived a gravitational field as a
geometrical warping of 4-D space and time.
Near a Black Hole
4. Which is most responsible for the ocean
tides?
 (a) ships
 (b) continental drift
 (c) the moon
 (d) the sun

5. If the sun were twice as massive
 (a) the pull of the earth on the sun would
double.
 (b) its pull on the earth would double.
 (c) both of these.
 (d) neither of these







14. The car moving at 50 kilometers/hour skids 10
meters with locked brakes. How far will the car
skid with locked brakes if it is traveling at 150
kilometers/hour?
(a) 20 meters
(b) 60 meters
(c) 90 meters
(d) 120 meters
(e) 180 meters
16. When a car is braked to a stop, its
kinetic energy is transformed to
 (a) stopping energy.
 (b) potential energy.
 (c) heat energy.
 (d) energy of rest.

End of Chapter 9
Pythagoras
(550 BC)

Claimed that natural
phenomena could be
described by
mathematics
Aristotle
(350 BC)

Asserted that the
universe is governed
by physical laws

The ancient Greeks believed that the earth
was at the center of a revolving sphere with
stars on it.

The Geocentric Model implies Earth-Centered
Universe.
Copernicus
(1500's)

Developed a
mathematical model
for a Sun-centered
solar system
Tycho Brahe
(1500's)

Made precise
measurements of the
positions of the
planets
Kepler
(1600's)

Described the shape of
planetary orbits
as well as their orbital
speeds
Kepler’s First Law

The orbit of a planet
about the Sun is an
ellipse with the Sun at
one focus.
Kepler’s Second Law

A line joining a
planet and the Sun
sweeps out equal
areas in equal
intervals of time.
Kepler’s Third Law

The square of a planet's orbital period is
proportional to the cube of the length of its
orbit's semimajor axis.

Or simply… T2 = R3
if T is measured
in years and R is measured in astronomical
units.
An Astronomical Unit...

…is the average distance of the Earth from
the Sun.

1 AU = 93,000,000 miles = 8.3 lightminutes
Kepler’s Laws

These are three laws of physics that
relate to planetary orbits.

These were empirical laws.

Kepler could not explain them.
Kepler’s Laws...Simply
(See page 192.)

Law 1: Elliptical orbits…

Law 2: Equal areas in equal times…

Law 3: T2 = R3