Level 4: Gravity everywhere

Gravity and orbits · level 4 of 8 · rough age 11-12 (a guide for parents; anyone can start anywhere)

Newton's big idea was that the pull that drops an apple is the same pull that holds the Moon. In this level you follow his reasoning, find out how gravity weakens with distance, see why outer planets go round more slowly, explain why astronauts float though gravity is still there, visit the two small moons of Mars and work out what it takes to escape a planet for good.

Lesson	You will be able to
The apple and the Moon	Follow Newton's comparison of a falling apple and the falling Moon
Weaker with distance	Use the inverse square rule: twice as far, a quarter of the pull
Slower farther out	Compare the speeds and years of the planets, and explain the pattern
Weightless in orbit	Explain why astronauts float, and how a ship to Mars could make its own gravity
Phobos and Deimos	Describe the moons of Mars, how they move in its sky, and what you would weigh on them
Escaping	Say what escape speed means and compare it for Earth, Mars, the Moon and Phobos

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