Transcript Document
Chapter 20 Section 3 The Earth Takes Shape Objectives • Describe the formation of the solid Earth. • Describe the structure of the Earth. • Explain the development of Earth’s atmosphere and the influence of early life on the atmosphere. • Describe how the Earth’s oceans and continents formed. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth • The Earth is mostly made of rock. Nearly three-fourths of its surface is covered with water. • Our planet is surrounded by a protective atmosphere of mostly nitrogen and oxygen, and smaller amounts of other gases. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • The Earth formed as planetesimals in the solar system collided and combined. • From what scientists can tell, the Earth formed within the first 10 million years of the collapse of the solar nebula. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • The Effects of Gravity When a young planet is still small, it can have an irregular shape. As the planet gains more matter, the force of gravity increases. • When a rocky planet, such as Earth, reaches a diameter of about 350 km, the force of gravity becomes greater than the strength of the rock. • As the Earth grew to this size, the rock at its center was crushed by gravity and the planet started to become round. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • The Effects of Heat As the Earth was changing shape, it was also heating up. As planetesimals continued to collide with the Earth, the energy of their motion heated the planet. • Radioactive material, which was present in the Earth as it formed, also heated the young planet. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • After Earth reached a certain size, the temperature rose faster than the interior could cool, and the rocky material inside began to melt. • Today, the Earth is still cooling from the energy that was generated when it formed. • Volcanoes, earthquakes, and hot springs are effects of this energy trapped inside the Earth. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion Objectives • Explain the difference between rotation and revolution. •Describe three laws of planetary motion. • Describe how distance and mass affect gravitational attraction. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion A Revolution in Astronomy • Each planet spins on its axis. The spinning of a body, such a planet, on its axis is called rotation. • The orbit is the path that a body follows as it travels around another body in space. • A revolution is one complete trip along an orbit. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion Earth’s Rotation and Revolution Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion A Revolution in Astronomy, continued • Johannes Kepler made careful observations of the planets that led to important discoveries about planetary motion. • Kepler’s First Law of Motion Kepler discovered that the planets move around the sun in elliptical orbits. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion Ellipse Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion A Revolution in Astronomy, continued • Kepler’s Second Law of Motion Kepler noted that the planets seemed to move faster when they are close to the sun and slower when they are farther away. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion A Revolution in Astronomy, continued • Kepler’s Third Law of Motion Kepler observed that planets more distant from the sun, such as Saturn, take longer to orbit the sun. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion Newton to the Rescue! • Kepler did not understand what causes the plans farther from the sun to move slower than the closer planets. • Sir Isaac Newton’s description of gravity provides an answer. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion Newton to the Rescue! continued • The Law of Universal Gravitation Newton’s law of universal gravitation states that the force of gravity depends on the product of the masses of the objects divided by the square of the distance between the objects. • According to this law, if two objects are moved farther apart, there will be less gravitational attraction between them. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion Newton to the Rescue! continued • Orbits Falling Down and Around Inertia is an object’s resistance to change in speed or direction until an outside force acts on the object. • Gravitational attraction keeps the planets in their orbits. Inertia keeps the planets moving along their orbits. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Section 4 Planetary Motion Gravity and the Motion of the Moon Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Standardized Test Preparation Interpreting Graphics The diagram below models the moon’s orbit around the Earth. Use the diagram below to answer the questions that follow. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Standardized Test Preparation 1. Which statement best describes the diagram? A Orbits are straight lines. B The force of gravity does not affect orbits. C Orbits result from a combination of gravitational attraction and inertia. D The moon moves in three different directions depending on its speed. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Standardized Test Preparation 1. Which statement best describes the diagram? A Orbits are straight lines. B The force of gravity does not affect orbits. C Orbits result from a combination of gravitational attraction and inertia. D The moon moves in three different directions depending on its speed. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Standardized Test Preparation 2. In which direction does gravity pull the moon? F toward the Earth G around the Earth H away from the Earth I toward and away from the Earth Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Standardized Test Preparation 2. In which direction does gravity pull the moon? F toward the Earth G around the Earth H away from the Earth I toward and away from the Earth Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Standardized Test Preparation 3. If the moon stopped moving, what would happen? A It would fly off into space. B It would continue to orbit the Earth. C It would stay where it is in space. D It would move toward the Earth. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 20 Standardized Test Preparation 3. If the moon stopped moving, what would happen? A It would fly off into space. B It would continue to orbit the Earth. C It would stay where it is in space. D It would move toward the Earth. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.