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Author Topic: How do objects orbit in space?  (Read 636 times)

Offline thedoc

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How do objects orbit in space?
« on: 12/04/2016 03:50:02 »
Leslie Wolf  asked the Naked Scientists:

My question is about orbiting bodies, and Earth's orbit in particular.

Is this statement correct: All orbiting bodies in the vacuum of space are perpetually free-falling faster and faster while encircling the larger body, but maintaining a constant distance from the larger body, because of their sideways speed, which, together with gravity, creates the circular orbit.

Many thanks for your answer,
Leslie Wolf.

What do you think?
« Last Edit: 12/04/2016 09:02:41 by chris »


 

Offline evan_au

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Re: How do objects orbit in space?
« Reply #1 on: 12/04/2016 11:56:33 »
Quote from: Leslie Wolf
Is this statement correct: All orbiting bodies in the vacuum of space are perpetually free-falling faster and faster while encircling the larger body, but maintaining a constant distance from the larger body, because of their sideways speed, which, together with gravity, creates the circular orbit.

I can modify it slightly to become a more accurate statement:
Quote
orbiting bodies in the vacuum of space are perpetually free-falling while encircling the larger body, but maintaining a constant distance from the larger body, because of their constant sideways speed, which, together with gravity, creates the circular orbit.

Where it went off track:
  • all orbiting bodies: Most orbiting bodies are not in circular orbits (with the larger body at the center), but an ellipse (a squashed circle), with the larger body at one of the two focal points of the ellipse. Even if you launched a satellite on a circular orbit around the Sun, it would not stay that way for very long, because the tug of other planets in the solar system would distort it into an ellipse.
  • free-falling faster and faster: If you dropped an object off a high building (in a vacuum), the longer it fell, the faster it would go. In this case, it is free-falling faster and faster. But this is a poor model for an an object in a circular orbit - for one thing, as it falls, it is getting closer to the Earth.
  • faster and faster: An object in a circular orbit maintains a constant speed as it progresses around its circular orbit.
  • faster and faster: Perhaps recently you saw an animation of two black holes colliding? In this case, they did go faster and faster as they spiraled inwards, but this only occurs in extremely strong gravitational fields, and does not apply to any detectable amount in the Solar system (or anywhere else I would like to be). But this is not a circular orbit - it is a spiral.
« Last Edit: 12/04/2016 19:05:35 by evan_au »
 

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Re: How do objects orbit in space?
« Reply #1 on: 12/04/2016 11:56:33 »

 

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