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River flow on a planet or large object.

  1. Aug 26, 2011 #1
    So let's say we have a planet not too dissimilar in size to those in our Solar System.

    It doesn't have to be spherical.

    But let's say we want a river to flow round the object.

    We want the flow to last as long as possible.

    We can consider two cases seperately: in our Solar system (with the Sun), and in isolation (no Sun).

    So what shape should the planet be, how big should it be, how fast should it be rotating, and how/how fast/ what direction should the river be flowing in order to create the best system for the river to flow as long as possible (i.e. it will have to slow down with time, but what is the way it will slow the rapidly)?

    Question: How can the river flow round an object that has an irregular shape?
    Answer: You aren't allowed to make a tiny circular river, but have to make one that you can recognize as going (reasonably close to) the greatest outer geodesic of the (possibly) irregular shape.

    Question: What is the planet made of?
    Answer: Again, you get to decide.

    This isn't a competition but I'm interested in hearing your ideas and thoughts on this one, as I have thought about it a few times in the past.
     
  2. jcsd
  3. Aug 26, 2011 #2
    A bigger sphere is flatter and so water will flow more slowly.....as it will if the mass of the planet is smaller so gravitational pull on the water is reduced....
     
  4. Aug 26, 2011 #3
    Ultimately the water will only need to flow from a high gravitic potential to a low one. Since I get to decide exactly what the planet is made of, my planet is similar in proportions to a RAZR phone. It is very thin, about 50m wide, and inifinitely long.

    The imaginary material goes from being near infinitely dense on one end, to twice the density of water on the other end, and the river flows along the length.
     
  5. Aug 26, 2011 #4

    DaveC426913

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    What? Why would this be so? As far as the river is concerned, it is on a flat, plane of uniform equipotential. Greater or lesser curvature of the planet will not change this.

    While true, a larger planet may have a larger gravity, that is beside the point you were making about curvature.
     
  6. Aug 26, 2011 #5
    A larger sphere is more flat at the surface. If a planet were 10m in diameter, I think the river certainly would be 'concerned' about the curvature!
     
  7. Aug 26, 2011 #6

    DaveC426913

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    Why?

    Again, the river thinks it's on a flat plane (albeit a small one). It knows nothing of curvature.
     
  8. Aug 26, 2011 #7
    I think what he's saying is that a larger sphere could accomodate a larger river. In a way I think we are both wrong, in that the river doesn't think anything. Its molecules are just obeying the forces at hand.
     
  9. Aug 26, 2011 #8
    I would have a circular planet with a huge volcano at the equator. The underground water would turn to steam and travel up through vents in the volcano. At the top, in the caldera would be an immense lake to cool the steam. I would insert a vent to allow the water to stream down the side of the volcano much like the spillway on a dam. The river bed would be a cut channel at the base of the volcano with a continuous grade of 1 inch drop per 4 foot in length. This channel would then circle the planet until it returned the water to the base of the volcano, and dropped back down to the underground reservoir to be turned into steam again.

    A huge thermal hydraulic lift system. The volcano provides the heat to lift the water (steam). The caldera lake acts as a condenser. The river channel acts as a gravity feed (pipe) to return the water to its source under the volcano after it circles the planet. :)
     
  10. Aug 26, 2011 #9
    My planet would be round with a channel cut at the equator filled with water. As the planet rotates the tidal effect from its sun would continously keep the river flowing around the planet.
     
  11. Aug 26, 2011 #10

    Drakkith

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    That's not a flow of water, that's a tide. You can think of it as 2 waves that travel across the planet as it rotates.
     
  12. Aug 26, 2011 #11

    Drakkith

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    This question doesn't really make any sense. The macroscopic properties of a planet, such as it's size and shape, don't really affect a river on it's surface as much as smaller things that only exist on a smaller scale. (And obviously a planet is required to be of a minimum amount of mass to become spherical, so shape doesn't really mean anything)

    Are we wanting to factor in current speed? Are we allowed to use precipitation to refill the river or are we working off of a finite amount of water?
     
  13. Aug 27, 2011 #12
    A river is flowing water. In this scenario the water flows and it satisfies the criteria from the OP. The water flows.
     
  14. Aug 27, 2011 #13

    Drakkith

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    I don't think the flowing of water through tidal effects is what the OP had in mind. I don't see how you could consider it "flowing".
     
  15. Aug 27, 2011 #14
    A bigger sphere isn't actually flatter, but it does APPEAR flatter to someone on the surface. This was the point being made.
     
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