2. Gravity: A Force of Attraction Chapter 19 Matter in Motion Section 4

3. The Effects of Gravity on Matter O Gravity is a force of attraction between objects due to their masses. O All matter has mass. Gravity is a result of mass. Therefore, all matter is affected by gravity. O This gravitational force pulls objects toward each other.

4. The Effects of Gravity on Matter O Since gravity is an attraction between objects due to their mass and you have mass, why don’t you see this happening? O The answer… you are too small.

5. The Size of the Earth’s Gravitational Force O Earth has a huge mass. O Earth’s gravitational force is very large. O Earth's gravitational force pulls everything toward the center of the Earth.

6. Newton and the Study of Gravity O When Newton was sitting under the apple tree and the apple fell and hit him in the head, he knew an unbalanced force caused the apple to fall. O He also concluded that an unbalanced force kept the moon revolving around the Earth. O He proposed that these 2 forces were the same force GRAVITY.

7. Newton and the Study of Gravity O Newton came up with the law now known as the law of universal gravitation. O This law describes the relationship between gravity, mass, and distance. O It is universal because it applies to all objects in the universe.

8. The Law of Universal Gravitation O All objects in the universe attract each other through gravitational force. O The size of the force depends on the masses of the objects.

9. Gravitational Force Increases as Mass Increases O Example: elephant and a cat O Example: Astronauts walking on moon

10. Gravitational Force Decreases as Distance Increases O Example: Earth’s distance from the sun O If you could stand on the sun, the gravity would be so strong you would not be able to move

11. The Differences Between Weight and Mass O Weight is a measure of gravitational force on an object. O Mass is the amount of matter in an object. O They are not the same. An object’s mass does not change. O If you were on Jupiter your weight would change, but your mass would be the same.

12. Units of Weight and Mass O The SI unit for force is a newton(N). O Gravity is a force, and weight is a measure of gravity. So weight is also measured in newtons. O The SI unit for mass is the Kilogram(kg). Mass is often measured in grams(g) and milligrams(mm). O On Earth, a 100g object (an apple) weighs about 1 newton