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Q & A: Why does Pluto orbit the Sun?

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Most recent answer: 09/21/2014
Q:
I'm having a hard time accepting that Pluto is kept in orbit around our Sun by gravity. I say this because by visualizing the Sun as a size of a tennis ball, Pluto would be the size of a grain of sand just over 300m away. My understanding of gravity is that it is a relatively 'weak' force. How on earth then does gravity account for Puto's orbit around the Sun. Please HELP!
- Mark Edwoods (age 52)
South Africa
A:

It's true that Pluto is far from the Sun. That means that it accelerates less toward the Sun than doe closer planets.  That's ok because it orbits so slowly that very little acceleration is needed to keep it in orbit. The basic mathematical pattern was discovered by Kepler: the square of the orbital period is proportional to the cube of the distance. Newton figured out that meant that the acceleration toward the Sun was inversely proportional to the square of the distance to the Sun.

Mike W.


(published on 09/21/2014)

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