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GRAVITY

GRAVITY. GALILEO GALILEI. FALLING BODIES. “ All falling objects accelerate at the same constant rate”. The link below shows a video of the Apollo 15 hammer and feather experiment on the Moon. http://vesuvius.jsc.nasa.gov/er/seh/feather.html. Acceleration is same for ALL OBJECTS ,

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GRAVITY

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  1. GRAVITY
  2. GALILEO GALILEI FALLING BODIES “All falling objects accelerate at the same constant rate” The link below shows a video of the Apollo 15 hammer and feather experiment on the Moon. http://vesuvius.jsc.nasa.gov/er/seh/feather.html
  3. Acceleration is same for ALL OBJECTS, regardless of mass! Acceleration due to gravity, g= 9.81 m s-2 M m F = ma F = ma a = g ! a = g again !! F = Mg [g = field strength] F = mg
  4. Newton’s Law of Universal Gravitation Every mass attracts every other mass with an attractive force which is directly proportional to the product of the masses and inversely proportional to the square of the separation between them. F F
  5. AN INVERSE SQUARE LAW F F r M1 M2 The negative sign merely indicates that the force and the distance are measured in opposite directions. G = the universal constant of gravitation G = 6.67 x 10-11 N m2 kg-2
  6. Force never reaches zero. Newton’s Inverse Square Law of Gravitation
  7. Example1: Jane, whose mass is 63kg, is standing 0.65m from John, whose mass is 82kg. Calculate the gravitational force attracting them towards each other. Solution: Fg = GMm r2 = 6.67 x 10-11 x 63 x 82  0.652 = 8.2 x 10-7 N
  8. r m = 1 kg M F GRAVITATIONAL FIELD STRENGTH The Gravitational Field Strength at a point, P, is the force that a mass of 1kg would experience at that point. P m = 1 kg Units = N kg-1
  9. Value at Earth’s surface Variation of g with distance, r from the Earth Obeys the INVERSE SQUARE law
  10. Field Strength is a VECTOR quantity Field Lines show the direction of the field. Earth’s Surface On a large scale, gravity field lines are radial. On a small scale, the field can be regarded as uniform.
  11. Example 2: Calculate the gravitational field strength g at the surface of the Earth. (The mass of the Earth is 5.98 x 1024kg and the radius is 6370Km.) SOLUTION: Distances from Earth are measured from its centre of mass. The distance of the surface of earth from its centre of mass at its radius. g = GM  r2 g = 6.67 x 10-11 x 5.98 x 1024  (6.37 x 106)2 [6370 km = 6.37 x 106] g = 9.83 Nkg-1
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