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Orbits Objectives: (i) analyse circular orbits in an inverse square law field by relating the gravitational force to the centripetal acceleration it causes; (j) define and use the period of an object describing a circle; (k) derive the equation T2 = 4 π2 x r3 GM from first principles; (l) select and apply the equation T2 = 4 π2 x r3 GM for planets and satellites (natural and artificial); (m) select and apply Kepler’s third law T 2 = k r 3 to solve problems; (n) define geostationary orbit of a satellite and state the uses of such satellites. Outcomes ALL MUST Be able to define the period of an object describing a circle. Be able to look at data like period, radius, gravitational field strength, to relate gravitational force to acceleration. Be able to define a geostationary orbit of a satellite and state the uses of such satellites. MOST SHOULD Be able to select and apply Kepler’s third law T 2 = k r 3 to solve problems in different situations. Be able to select and apply the equation T2 = 4 π2 x r3 GM correctly for planets and satellites (natural and artificial); SOME COULD Be able to derive the equation T2 = 4 π2 x r3 GM from first principles; 1.Gravity 17th Century England… A man sits in an orchard and ponders the universe… Why do things always fall downwards and never upwards? Why do the planets orbit around the sun? Why does the moon orbit around the earth? Of course there must be an invisible force that acts between all things! The force is GRAVITY Gravity is an attractive, non-contact force that acts between all objects. The bigger the object the greater the force of gravity. The further the objects are from each other the less the force of gravity. The further the objects are from each other the less the force of gravity. 2. Orbits Cannon Simulator • http://jersey.uoregon.edu/vlab/Cannon/