ch 13 gravitational interactions. newton did not discover gravity. he discovered that gravity is...

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Ch 13 Gravitational Interactions Slide 2 Newton DID NOT discover gravity. He discovered that gravity is universal. - It pulls everything with the same force. Slide 3 He also discovered that all objects in the universe attract each other. Slide 4 A force field exerts a force on objects in its vicinity. Slide 5 Gravitational Field (g) A force field that exists in the space around every mass or groups of masses. Slide 6 The strength of a gravitational field is the force per unit mass. g = F/m Slide 7 Newtons Law of Universal Gravitation Slide 8 Slide 9 Using the earths radius and mass we get 9.8 m/s 2. Slide 10 Remember at or near the earths surface the gravitational field strength is 9.8 m/s 2 or 10 m/s 2. Slide 11 The acceleration due to gravity, g, decreases with distance from the earths center as 1/d 2. Slide 12 As an object moves away from the center of the Earth, by a distance equivalent to the earths radius. Slide 13 Slide 14 Distance Force of Gravity RERE FgFg 2 R E 1/4 F g 3 R E 1/9 F g 4 R E 1/16 F g 5 R E 1/25 F g Slide 15 Gravitational Field Inside a Planet There exist a gravitational field inside the earth as well as outside. Slide 16 As you get closer to the center of the earth the gravitational acceleration decreases. Slide 17 When you get to the center of the earth your acceleration is zero. There is no gravitational field at the center of the earth The mass above and below you cancel each other out. Slide 18 Weight (F g ) The force of gravity. The pressing against the earth is the sensation we interpret as weight. Slide 19 Think about being in an elevator. Slide 20 Slide 21 Stage A Stage B Stage C Stage D F net = ma F net = 0 N F net = ma F net = 400 N, up F net = ma F net = 400 N, down F net = ma F net = 784 N, down F N equals F g F Norm = 784 N F N > F g by 400 N F Norm = 1184 N F N < F g by 400 N F Norm = 384 N F N < F g by 784 N F Norm = 0 N Slide 22 This last situation is the reasoning you might feel a little queasy in the stomach when you go over a good size bump in the road at a really fast speed or sudden drops on roller coasters. You catch a little air and the seat drops out from you briefly. Slide 23 Rather than define weight as the force of gravity that acts on you. We can say that it is the force you exert on a supporting floor. Slide 24 Weightlessness Is not the absence of gravity, rather it is the absence of a support force. Slide 25 Newton showed that the ocean tides are caused by differences of the moons gravitational pull on opposites sides of the earth. Slide 26 When the sun, Earth, and the moon are all lined up, the tides due to the moon and sun coincide. Slide 27 Resulting in higher than average high tide and lower than average low tides. These are called spring tides. Slide 28 Slide 29 Lunar Eclipse Is produced when earth is directly between the sun and the moon. Slide 30 Slide 31 Solar Eclipse Is produced when the moon is directly in between the earth and sun. Slide 32 Slide 33 Slide 34 Neap Tides When there is a half moon, the sun and moon partly cancel each other out. Produces lower than average high tides and lower than average low tides. Slide 35 Slide 36 Slide 37 Black Hole A mass that has collapsed to so great a density that its enormous local gravitational field prevents light from escaping. Slide 38 Anatomy of a Black Hole Black Holes