1. 15-May-15 Physics 1 (Garcia) SJSU Chapter 9 Gravity

2. 15-May-15 Physics 1 (Garcia) SJSU Newton and the Moon Newton realized that Earth’s gravity was the centripetal force that kept the moon in orbit. Also discovered that gravity was weaker at that great distance. Gravity force

3. 15-May-15 Physics 1 (Garcia) SJSU Gravity & Distance We don’t notice that gravity gets weaker as we move away from Earth because we rarely go very far. Moon is 30 Earth diameters away

4. 15-May-15 Physics 1 (Garcia) SJSU Universal Law of Gravity Force of gravity has magnitude given by (Gravity Force) = (G) x Object A Object B ( Mass of Object A ) x ( Mass of Object B) ( Distance ) x ( Distance ) DISTANCE Force Equal and opposite forces (Newton’s Third law)

5. 15-May-15 Physics 1 (Garcia) SJSU Universal Gravity Constant, G In the formula for gravity force, we have G = 0.0000000000667 N m 2 / kg 2 = 6.67 x 10 –11 N m 2 / kg 2 The formula and the constant are called “universal” because, up to now, this theory predicts gravity anywhere in the universe.

6. 15-May-15 Physics 1 (Garcia) SJSU Cavendish Experiment For non-astronomical objects gravity force is very small. Need sensitive balance to detect. First measured by Cavendish in his home laboratory in 1797 at age 67.

7. 15-May-15 Physics 1 (Garcia) SJSU “Intelligent Falling” "Things fall not because they are acted upon by some gravitational force, but because a higher intelligence, 'God' if you will, is pushing them down," The Onion, August 17, 2005 Universal Law of Gravity

8. 15-May-15 Physics 1 (Garcia) SJSU Sample Problem Here is an example of using the formula (Gravity Force) = (G) x ( Mass of Object A ) x ( Mass of Object B) ( Distance ) x ( Distance ) DISTANCE = Earth’s Radius Force Object B (Earth) Object A (1 kg mass)

9. 15-May-15 Physics 1 (Garcia) SJSU Sample Problem Find gravity force for a 1 kg mass on surface of Earth. (Force) = (6.67 x 10 –11 ) x Value comes out to 9.8 Newtons (check this with your calculator; it’s good practice). ( 1 ) x ( 6 x 10 24 ) ( 6.38 x 10 6 ) 2 Universal Gravity Constant, G Earth’s Radius Earth’s Mass

10. 15-May-15 Physics 1 (Garcia) SJSU Sample Problem (cont.) Find gravity acceleration on a 1 kg mass. Using Newton’s Second Law, (Acceleration) = = Answer is 9.8 m/s 2, which we’ve been rounding off as 10 m/s 2. (Force) (Mass) ( 9.8 N ) (1 kg )

11. 15-May-15 Physics 1 (Garcia) SJSU Inverse Square Law Gravity force weakens with distance as the inverse of the square of the distance. Geometric property of area and distance. Outer circle is twice Earth’s radius so it has 4 times the area Earth Gravity 1/4 Earth Gravity

12. 15-May-15 Physics 1 (Garcia) SJSU Demo: Perspective These four figures are equally spaced in distance and, in perspective, you are standing that distance from the first. At twice the distance, the face is ¼ the size. At four times the distance face is 16 th the size.

13. 15-May-15 Physics 1 (Garcia) SJSU Demo: Perspective Cards Hold large card at arm’s length. Close one eye then hold small card at a distance such that it is same size as large card. That distance will be half way between your eye and large card. 1 12 34 Arm’s length Half

14. 15-May-15 Physics 1 (Garcia) SJSU Weightlessness In deep space, far away from all stars, planets, etc. there is almost no gravity force. In orbit near Earth, gravity is still strong (only 10% less than on surface). Why are Shuttle and Space Station astronauts “weightless”? Earth is nearby

15. 15-May-15 Physics 1 (Garcia) SJSU Freefall & Weightlessness Freefall is a state of weightlessness, even though gravity is present.

16. 15-May-15 Physics 1 (Garcia) SJSU Movie: Roller Coaster

17. 15-May-15 Physics 1 (Garcia) SJSU Check Yourself Sit in a seat on Ferris wheel. Where do you feel heaviest? Where do you feel lightest? E A B C D Velocity Centripetal Force

18. 15-May-15 Physics 1 (Garcia) SJSU Demo: Ferris Wheel in Hand Place a heavy object in your hand, hold your arm out and rotate your arm, palm upward, in a small circle. Object will feel lightest at the top of the circle and heaviest at bottom. Support Force Support Force

19. 15-May-15 Physics 1 (Garcia) SJSU Demo: Falling Slinky Hold a Slinky and its weight stretches it out. Now drop it. In freefall it’s in a state of weightlessness so Slinky immediately contracts.

20. 15-May-15 Physics 1 (Garcia) SJSU NASA’s “Vomit Comet” NASA has a special airplane for training astronauts in free- fall weightless conditions. The “Vomit Comet” nickname tells you it’s quite a wild roller-coaster ride. The plane flies between 20,000 and 30,000 feet, same as commercial flights.

21. 15-May-15 Physics 1 (Garcia) SJSU Power Climb Weightless Freefall Pull out of Dive Flight of the “Vomit Comet” At the top of the arc, the plane’s trajectory is projectile motion. Boeing 707 (modified)