Upload
almujhool
View
219
Download
2
Embed Size (px)
Citation preview
Copyright © 2010 Pearson Education, Inc.
The Motions of the Planets
The Birth of Modern Astronomy
The Laws of Planetary Motion
Newton’s Laws
Summary of Chapter 1
Units of Chapter 1
Copyright © 2010 Pearson Education, Inc.
The Sun, Moon, and stars all have simple movements in the sky, consistent with an Earth-centered system.
Planets:• Move with respect to fixed stars• Change in brightness• Change speed• Have retrograde motion• Are difficult to describe in earth-centered system
1.1 The Motions of the Planets
Copyright © 2010 Pearson Education, Inc.
1.1 The Motions of the PlanetsA basic geocentric model, showing an epicycle (used to explain planetary motions)
Copyright © 2010 Pearson Education, Inc.
1.1 The Motions of the PlanetsLots of epicycles were needed to accurately track planetary motions, especially retrograde motions. This is Ptolemy's model (140 A.D).
Copyright © 2010 Pearson Education, Inc.
• Aristarchus (310-230 B.C.) proposed that all the planets including Earth revolve around the Sun. Also that Earth rotates on its axis once each day.
Copyright © 2010 Pearson Education, Inc.
By 300 B.C., Aristotle presented naked-eye observations for the Earth’s spherical shape. How did he observe it?
Copyright © 2010 Pearson Education, Inc.
Non-Western Contributions• Islamic Contributions
– Relied on celestial phenomena to set its religious calendar
– Created a large vocabulary still evident today (e.g., zenith, Betelgeuse)
– Developed algebra and Arabic numerals• Asian Contributions
– Devised constellations based on Asian mythologies
– Kept detailed records of unusual celestial events (e.g., eclipses, comets, supernova, and sunspots)
– Eclipse predictions
Copyright © 2010 Pearson Education, Inc.
1.1 The Motions of the PlanetsCopernican model of the solar system (at about 1500 A.D). A heliocentric (Sun-centered) model of the solar system easily describes the observed motions of the planets, without excess complication.
Copyright © 2010 Pearson Education, Inc.
By 300 B.C., Aristotle presented naked-eye
observations for the Earth’s spherical shape
Copyright © 2010 Pearson Education, Inc.
1.2 The Birth of Modern AstronomyIn 1609 Galileo built a telescope for himself. Observations of Galileo:
• The Moon has mountains, valleys, and craters.
• The Sun has imperfections, and it rotates.
• Jupiter has moons.
• Venus has phases.
All these were in contradiction to the general belief that the heavens were constant and immutable.
Copyright © 2010 Pearson Education, Inc.
1.2 The Birth of Modern AstronomyThe phases of Venus are impossible to explain in the Earth-centered model of the solar system.
Copyright © 2010 Pearson Education, Inc.
1. Planetary orbits are ellipses, Sun at one focus.Kepler’s laws:
1.3 The Laws of Planetary Motion
Copyright © 2010 Pearson Education, Inc.
2. Imaginary line connecting Sun and planet sweeps out equal areas in equal times.
Kepler’s laws:
1.3 The Laws of Planetary Motion
Copyright © 2010 Pearson Education, Inc.
3. Square of period of planet’s orbital motion is proportional to cube of semimajor axis.
Kepler’s laws:
1.3 The Laws of Planetary Motion
Copyright © 2010 Pearson Education, Inc.
Question 12
Earth is closer to the Sun in January. From this fact, Kepler’s 2nd law tells us
a) Earth orbits slower in January.
b) Earth orbits faster in January.
c) Earth’s orbital speed doesn’t change.
Copyright © 2010 Pearson Education, Inc.
Earth is closer to the Sun in January. From this fact, Kepler’s 2nd law tells us
a) Earth orbits slower in January.
b) Earth orbits faster in January.
c) Earth’s orbital speed doesn’t change.
Kepler’s 2nd law means that a planet moves faster
when closer to its star.
FasterSlower
Question 12
Copyright © 2010 Pearson Education, Inc.
• https://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/0073512176/78778/Kepler_Nav.swf::Keplers%20Second%20Law%20Interactive
Copyright © 2010 Pearson Education, Inc.
Question 13
Kepler’s 3rd law relates a planet’s distance from the Sun and its orbital
a) speed.b) period.c) shape.d) velocity.
Copyright © 2010 Pearson Education, Inc.
Kepler’s 3rd law relates a planet’s distance from the Sun and its orbital
a) speed.b) period.c) shape.d) velocity.
Kepler’s 3rd law
P2 = a3
means more distant planets orbit more slowly.
Question 13
Venus’ period = 225 days
Venus’ axis = 0.7 AU
Earth’s period = 365 days
Earth’s axis = 1.0 AU
Copyright © 2010 Pearson Education, Inc.
1.3 The Laws of Planetary MotionThe Dimensions of the solar system• The distance from Earth to the Sun is called an astronomical unit. Its actual length may be measured by bouncing a radar signal off Venus and measuring the transit time.
Copyright © 2010 Pearson Education, Inc.
Newton’s laws of motion explain how objects interact with the world and with each other.
Newton’s first law:
An object at rest will remain at rest, and an object moving in a straight line at constant speed will not change its motion, unless an external force acts on it.
1.4 Newton’s Laws
Copyright © 2010 Pearson Education, Inc.
Newton’s second law:
When a force is exerted on an object, its acceleration is inversely proportional to its mass:
a = F/mNewton’s third law:
When object A exerts a force on object B, object B exerts an equal and opposite force on object A.
1.4 Newton’s Laws
Copyright © 2010 Pearson Education, Inc.
Gravity
On Earth’s surface, the acceleration due to gravity is approximately constant, and directed toward the center of Earth.
1.4 Newton’s Laws
Copyright © 2010 Pearson Education, Inc.
Gravity
For two massive objects, the gravitational force is proportional to the product of their masses divided by the square of the distance between them.
1.4 Newton’s Laws
Copyright © 2010 Pearson Education, Inc.
Gravity
The gravitational pull of the Sun keeps the planets moving in their orbits.
1.4 Newton’s Laws
Copyright © 2010 Pearson Education, Inc.
1.4 Newton’s LawsMassive objects actually orbit around their common center of mass; if one object is much more massivethan the other, the center of mass is not far from the center of the more massive object. For objects more equal in mass, the center of mass is between the two.
Copyright © 2010 Pearson Education, Inc.
Kepler’s laws are a consequence of Newton’s laws.
1.4 Newton’s Laws
Copyright © 2010 Pearson Education, Inc.
Question 14
Newton’s law of gravity states that the force between two objects
a) increases with distance.b) depends on the state of matter
(solid, liquid, or gas).c) can be attractive or repulsive.d) increases with mass.
Copyright © 2010 Pearson Education, Inc.
Question 14
Newton’s law of gravity states that the force between two objects
a) increases with distance.b) depends on the state of matter
(solid, liquid, or gas).c) can be attractive or repulsive.d) increases with mass.
The attractive force of gravity INCREASES with greater mass, and DECREASES QUICKLY with greater
distance.
The force doesn’t depend on the kind of matter.
Copyright © 2010 Pearson Education, Inc.
• First models of solar system were geocentric, but couldn't easily explain retrograde motion.• Heliocentric model does.• Galileo's observations supported heliocentric model.• Kepler found three empirical laws of planetary motion from observations.
Summary of Chapter 1
Copyright © 2010 Pearson Education, Inc.
• Laws of Newtonian mechanics explained Kepler’s observations.• Gravitational force between two masses is proportional to the product of the masses, divided by the square of the distance between them.
•http://waowen.screaming.net/revision/force&motion/ncananim.htm
Summary of Chapter 1, cont.