9-12

I2: Explain some current theories of gravitational force.

Curriculum Organizing Questions	What is gravity? What causes gravity? How is gravity affected by changes in mass? distance? Compare Newton's theory of gravity and Einstein's general relativity.
Elaboration	Gravitational force is an attraction between masses. The strength of the force is proportional to the masses and weakens rapidly with increasing distance between them. Benchmarks 4G1.
Specific Ideas	Gravitation is a universal force that each mass exerts on any other mass. NSES B4b. The strength of the gravitational attractive force between two masses is proportional to the masses and inversely proportional to the square of the distances between them NSES B4b. Issac Newton created a unified view of force and motion. ... his mathematical analysis of gravitational force and motion showed that planetary orbits had to be the very ellipses that Kepler had proposed two generations earlier. Benchmarks 10B1. General relativity theory pictures Newton's gravitational force as a distortion of space and time. Benchmarks 10C4.
Developmental & Instructional Implications	A study of pupils 11-17 years revealed ideas of gravity "pushing", "pulling", or "holding". "Holding" appeared to be the most common perception of gravity and this was bound up with the ideas of gravity being connected with air pressing down and with an atmospheric shield which prevented things from floating away. ... Watts found that pupils 12-17 years thought that gravity dependson height, but they appeared to confuse gravity with potential energy in assuming a higher force of gravity at greater heights. ... There were also references to gravity as a kind of "material" which could be trapped in aeroplanes. Driver pgs. 163-164.
Examples

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