Astronomy › Section C · Orbits and gravity › Topic C.3
Newton's universal law of gravitation
Newton's boldest idea was that the force pulling an apple to the ground is the same force that holds the Moon in orbit and the planets around the Sun. One short equation describes it, and it lets astronomers weigh planets and stars they can never visit.
In this topic
- A force that bends orbits
- The law itself
- Worked example: the pull between Earth and the Moon
- The Moon test
- Weight, mass and surface gravity
- Worked example: weighing yourself on Mars
- Gravity never switches off
- Newton's version of Kepler's third law
- Worked example: weighing Jupiter with Io
- Common mistakes to avoid
- Key takeaways
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