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Gravity near the Earth’s Surface 5-6 and 5-7 Quick notes 1. The equation for the acceleration at the Earth’s surface is g=GmE/r2E 2. The mass of Earth can be calculated by: mE= g r2E / G 3. A satellite orbits because it is put into orbit by accelerating to a high enough tangential speed with rockets. If the speed is too high, it will escape Earth’s gravity, too low and it falls back to Earth. 4. When can calculate a satellite’s speed using this equation: v= GmE/r 5. When calculating w in an object or person that is accelerating in an object moving up or down (like an elevator) the person or object’s weight = mg +ma. 6. Apparent Weightlessness occurs when objects or people are free falling with an object and so the object appears not to have weight even though gravity is still acting on the object. This occurs when the acceleration is –g, so that w=mg-mg=0