unit 1 lesson 4 gravity and motion. down to earth copyright © houghton mifflin harcourt publishing...
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Unit 1 Lesson 4 Gravity and Motion
Down to Earth
Copyright © Houghton Mifflin Harcourt Publishing Company
What is gravity?• Gravity is a noncontact force of attraction between objects due to their mass.
• All objects on Earth fall at the same rate once air resistance and other factors are removed.
• The force of gravity between Earth and an object is equal to the mass of an object m multiplied by a factor due to gravity g.
• Force = mass × acceleration due to gravity
(F = mg), where g is about 9.8 m/s2.
Unit 1 Lesson 4 Gravity and Motion
What is gravity?
What is gravity?
• What if you drop a heavy object and a light object at the same time? Which would hit the ground first?
• Some objects can experience a lot of air resistance and fall slowly to the ground.
• If you take away air resistance, all objects will fall with the same acceleration.
• When gravity is the only force affecting the fall, a light object and a heavy object will hit the ground at the same time.
• What is gravity?
What is gravity?
• All matter has mass, so all matter is affected by gravity.
• All objects experience gravitational attraction to all other objects.
• Earth and other planets are round because of gravity.
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Unit 1 Lesson 4 Gravity and Motion
What is gravity?
• Some objects in space are not round because they are too small for gravity to shape them into a sphere.
• The paths of the planets, the sun, and our galaxy are determined by gravity.
• The sun’s gravity is the force that keeps the planets moving in orbit around the sun.
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Unit 1 Lesson 4 Gravity and Motion
What is gravity?
A Weighty Issue
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What determines the force of gravity?
• In 1687, Sir Isaac Newton formulated the law of universal gravitation.
• The law of universal gravitation states that all objects in the universe attract each other through gravitational force.
• The strength of the gravitational force is related to the mass of the objects and the distance between them.
Unit 1 Lesson 4 Gravity and Motion
What determines the force of gravity?
• Gravitational force between two objects increases as the distance between their centers decrease.
• Gravitational force between two objects increases as their masses increase.
• Objects with greater mass have more attraction between them than objects with smaller mass have between them.
• When the distance between two objects increases, the force of gravity decreases.
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Unit 1 Lesson 4 Gravity and Motion
What determines the force of gravity?
What determines the force of gravity?
Don’t Bring Me Down
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How does gravity keep objects in orbit?• Free fall is when gravity is pulling an object down and no other forces are acting on it.
• An object is in orbit when it travels around another object in space.
• When an object orbits Earth, it is moving forward but it is also in free fall.
• Forward motion and free-fall motion combine to cause orbiting.
Unit 1 Lesson 4 Gravity and Motion
How does gravity keep objects in orbit?
How does gravity keep objects in orbit?• Spacecraft, satellites, the moon, planets, and stars all complete orbits.
• Any object in curved motion is constantly changing direction.
• As the planets orbit the sun, or the moon orbits Earth, centripetal force keeps them moving inward in a circular path instead of flying off in a straight line.
• Gravity is the force that pulls objects toward the center of an orbital path.
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Unit 1 Lesson 4 Gravity and Motion
How does gravity keep objects in orbit?