Newton's law of gravitation
The gravitational force between two point masses is proportional to their product and inversely proportional to the square of the separation: F = GM₁M₂/r², where G = 6.67 × 10⁻¹¹ N·m²·kg⁻² is the gravitational constant. The force is always attractive, regardless of mass signs, and acts along the line joining the masses.
Formula
F = GM₁M₂/r²
Real World
The Voyager 1 probe's trajectory was calculated using Newton's law of gravitation across planetary distances; launched in 1977, it reached interstellar space precisely as predicted.
Exam Focus
In 'show that' questions, substitute values clearly and state that r is measured centre-to-centre for spherical masses to secure method marks.
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