1. Law of Universal Gravitation Chapter 12 November 9/10

2. Introduction All objects have gravity Therefore, all objects attract one another

3. 12.1 The Falling Apple An apple falls to Earth because of gravity Does Earth’s gravity pull the moon? – YES Why doesn’t the moon fall into Earth? – It does but it doesn’t crash because of tangential speed

4. 12.2 The Falling Moon Earth’s gravity pulls moon = centripetal force Moon falls beneath the straight line it would follow if no force acted on it – Below the tangential speed line Figure 12.2 Confirmed with experiment – Figure 12.4

5. 12.3 The Falling Earth Earth (and other planets)falls around the sun Why don’t planets crash into sun? – Because of tangential velocities What would happen if tangential speeds went away? – Crash into sun – This has happened to asteroids and other matter without a big enough tangential speed

6. Check for understanding In the picture below use vectors and words to describe how the Earth orbits the sun Sun Earth

7. 12.4 Newton’s Law of Universal Gravitation Newton discovered gravity is universal – Everything pulls on everything else Law of Universal Gravitation – “Every object attracts every other object with a force that for any two objects is directly proportional to the mass of each object” (Hewitt 172) – Greater masses = greater force of attraction – Greater distance (farther away) = less force of attraction

8. 12.4 Newton’s Law of Universal Gravitation (con’t) Law can be expressed as an equation