1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Universal Gravitation Sir Isaac Newton (1642–1727) gave us the law of universal gravitation. Universal Gravitation Equation m 1 and m 2 are the masses of the two objects d is the distance between the two objects G is a constant Section 2 Gravity Chapter 11

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Universal Gravitation All matter is affected by gravity. Two objects, whether large or small, always have a gravitational force between them. When something is very large, like Earth, the force is easy to detect. Gravitational force increases as mass increases. Gravitational force decreases as distance increases. Section 2 Gravity Chapter 11

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Universal Gravitation Section 2 Gravity Chapter 11

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Free Fall and Weight Free fall just gravity is acting on the body. Free-fall acceleration near Earth’s surface is constant. If we disregard air resistance, all objects near Earth accelerate at 9.8 m/s 2. Freefall acceleration is often abbreviated as the letter g, so g = 9.8 m/s 2. Section 2 Gravity Chapter 11

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Free Fall and Weight, continued Weight is the downward force exerted on objects due to gravity weight = mass  free-fall acceleration (m/s 2 ) w = mg Weight is different from mass. Mass is a measure of the amount of matter in an object. Weight is the gravitational force an object experiences because of its mass. Section 2 Gravity Chapter 11

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Free Fall and Weight, continued Velocity is constant when air resistance balances weight. Terminal velocity is this constant velocity –GRAVITY AND AIR RESISTANCE ARE EQUAL SO OJBECT STOPS ACCELERATING. A sky divers approximate terminal velocity before a parachute is 320 km/h Section 2 Gravity Chapter 11

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Terminal Velocity Section 2 Gravity Chapter 11 What happens after the parachute is opened? Air resistance increases Air resistance decreases Gravity changes Speed increases

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Free Fall and Motion Orbiting objects are in free fall. The moon stays in orbit around Earth because Earth’s gravitational force provides a pull on the moon. Two motions combine to cause orbiting. Section 2 Gravity Chapter 11