5Newton’s law of gravitation Attractive force between all massesProportional to product of the massesInversely proportional to separation distance squaredExplains why g=9.8m/s2Provides centripetal force for orbital motion
7Newton’s Law of Universal Gravitation From Kepler's 3rd Law, Newton deduced inverse square law of attraction.G=6.67 ´ N m2/kg2
8Gravity QuestionsDid the Moon exert a gravitational force on the Apollo astronauts?What kind of objects can exert a gravitational force on other objects?The constant G is a rather small number. What kind of objects can exert strong gravitational forces?
9Gravity QuestionsIf the distance between two objects in space is doubled, then what happens to the gravitational force between them?What is the distance is tripled?…is quadrupled?What if the mass of one of the object is doubled?…tripled?…quadrupled?
10Weight and Weightlessness the force due to gravity on an objectWeight = Mass Acceleration of GravityW = m g“Weightlessness” - a conditions wherein gravitational pull appears to be lackingExamples:AstronautsFalling in an ElevatorSkydivingUnderwater
11Ocean TidesThe Moon is primarily responsible for ocean tides on Earth.The Sun contributes to tides also.What are spring tides and neap tides?
194. Which is most responsible for the ocean tides? (a) ships(b) continental drift(c) the moon(d) the sun
205. If the sun were twice as massive (a) the pull of the earth on the sun would double.(b) its pull on the earth would double.(c) both of these.(d) neither of these
2114. The car moving at 50 kilometers/hour skids 10 meters with locked brakes. How far will the car skid with locked brakes if it is traveling at 150 kilometers/hour?(a) 20 meters(b) 60 meters(c) 90 meters(d) 120 meters(e) 180 meters
2216. When a car is braked to a stop, its kinetic energy is transformed to (a) stopping energy.(b) potential energy.(c) heat energy.(d) energy of rest.
34Kepler’s First LawThe orbit of a planet about the Sun is an ellipse with the Sun at one focus.
35Kepler’s Second LawA line joining a planet and the Sun sweeps out equal areas in equal intervals of time.
36Kepler’s Third LawThe square of a planet's orbital period is proportional to the cube of the length of its orbit's semimajor axis.Or simply… T2 = R3 if T is measured in years and R is measured in astronomical units.
37An Astronomical Unit...…is the average distance of the Earth from the Sun.1 AU = 93,000,000 miles = 8.3 lightminutes
38Kepler’s LawsThese are three laws of physics that relate to planetary orbits.These were empirical laws.Kepler could not explain them.
39Kepler’s Laws...Simply (See page 192.) Law 1: Elliptical orbits…Law 2: Equal areas in equal times…Law 3: T2 = R3