Newton's inverse-square law and G, how g varies with height, depth and latitude, gravitational potential and its negative sign, escape and orbital velocities, satellites and Kepler's laws.
Unit 1 carries 10 of the 50 physics marks; with eight chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). MEC names the chapter Gravity, but the physics in it is gravitation — the universal inverse-square attraction between any two masses — and the textbooks use that word throughout; the two names mean the same syllabus here.
The MEC scope line runs: Gravitational force, acceleration, field strength, energy and potential: laws, calculations and graphical treatment. The single heading below is that point; its subsections follow the order of the line — force, then acceleration, then field strength, then energy and potential, and the graphs last.
Three ways it comes. Recall: the value and unit of G, the escape velocity from the Earth, the height and period of a geostationary satellite, Kepler's three laws. Understanding: why gravitational potential is always negative, why g is greater at the poles than at the equator, why an astronaut in orbit is weightless without being beyond gravity, why the escape velocity does not depend on the mass or the direction of the projectile. Application: g at a stated height or depth, an orbital speed or period, a potential-energy change, a Kepler ratio.
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