# The Naked Scientists Forum

### Author Topic: Why does the Earth orbit the Sun?  (Read 771 times)

#### thedoc

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##### Why does the Earth orbit the Sun?
« on: 15/04/2014 00:30:01 »

In universe there are no external friction forces to stop motion, so then why does the 'earth' (and other planets) orbit the sun?
What do you think?
« Last Edit: 15/04/2014 00:30:01 by _system »

#### evan_au

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##### Re: Why does the Earth orbit the Sun?
« Reply #1 on: 12/04/2014 02:26:29 »
Isaac Newton identified that objects in a vacuum would continue in a straight line at a steady speed unless they were acted on by a force.
So the Earth, traveling at around 30 km/sec would go sailing out of the Solar System if it had no forces acting on it.

But Newton also identified that the mass of the Sun and the Earth produces a gravitational force on the Earth (and the Sun), which bends the Earth's path into a circular or elliptical orbit around the Sun.

It is possible to escape from the Sun's gravity, and go sailing off into interstellar space, but you need a much higher speed than you can achieve with today's chemical rockets. So the handful of spacecraft that have embarked on this journey have used a "gravitational slingshot" from Jupiter or other planets to put them on a hyperbolic path which will take them right out of the Solar System, and not return.

Note: The path of an object in a gravitational field from a star follows a circle, ellipse, parabola or hyperbola. These are a group of geometric shapes called "conic sections", which were known to Greek mathematicians several hundred years BC.

You can experiment with orbits using a game here: http://www.testtubegames.com/gravity_flash.html

#### The Naked Scientists Forum

##### Re: Why does the Earth orbit the Sun?
« Reply #1 on: 12/04/2014 02:26:29 »