What Makes a Stone Skip When Tossed Across a Pond?

Discussion in 'Hydrodynamics and Aerodynamics' started by Submarine Tom, Mar 29, 2012.

  1. Submarine Tom

    Submarine Tom Previous Member

    Is it planing when it strikes the water?

    Porpoising perhaps.

    Ah, momentum. What a wonderfull thing.

    Although, inertia certainly is hard to over come getting my butt out of bed in the morning!

    -Tom
     
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  2. gonzo
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    gonzo Senior Member

    Dynamic lift, they are planing.
     
  3. Petros
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    Petros Senior Member

    The lift the stone generates on the surface of the water is more than the weight of the stone, or it would sink. lift is a function of the speed, the angle of attack, the shape of the stone, the density of the water. All of these are the same factors that cause a boat hull to plane and rise up out of the water (reducing the wetted surface).

    The spinning of a stone is done mainly for stablity, so the flat side stays down.
     
  4. hoytedow
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    hoytedow Wood Butcher

    Same as common glass, which technically is a liquid. At one angle it skips and at another it drives on through.
     
  5. PAR
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    PAR Yacht Designer/Builder

    I've always bought into the gremlin theory on this one. How many of you remember this (without Googling) from grade school?
     
  6. mydauphin
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    mydauphin Senior Member

    It is all an illusion
     
  7. waikikin
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    waikikin Senior Member

    Maybe a philosophical question? It's often Boys & their Dads that make stones skip across the water.................. & the forces of youthful exuberance & the memory of it.
     
  8. Submarine Tom

    Submarine Tom Previous Member

    Waikikin,

    You are the closest!
     
  9. Frosty

    Frosty Previous Member

    It will skip over a lot of surfaces, grass---

    Barnes wallace bouncing bomb WW11 dropped at the right height bounced across the German dam to stop by the wall and sink down it.
     
  10. Submarine Tom

    Submarine Tom Previous Member

    Way off Froster, but thanks for coming out.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Don't tell me it has something to do with "suction", 'cos that seems to be the cause for everything when no-one knows the answer. I'm thinking surface tension plays a part.
     
  12. tunnels

    tunnels Previous Member

    Its a combination of many interesting things . speed , aerodynamics ,to hold tha stone in flight , Hydrodynamics when it hits the surface of the water and becomes airborn again but its loosing speed with each bounce so wetted surface friction is gradually becoming a problem, the bounces increase in regularity as the speed drops a shape begins to bite so the lack of hydrodynamics are really taking effect faster and faster everything is Happening to the poit where momentum reachs a point where it simply skims across the surface smoothly and then lack of bouyanceit finally sinks witha see sawing action as it finally settles in the mud at the bottom of a lake :confused:
     
  13. Frosty

    Frosty Previous Member


    http://www.chm.bris.ac.uk/webprojects2001/moorcraft/The Bouncing Bomb.htm

    I thought every one new about the bouncing bomb, regardless of its ultimate job it skimmed the surface.

    when dropped from the right hieght,--bounced across the surface of the resovoiur until its slowed and sank at the right place. You say' way off'--how so its a skimming stone --identical.

    Barns Wallace also invented the Jet engine. Surley Barns Wallace has not been forgotten already, he won the war.
     
  14. rxcomposite
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    rxcomposite Senior Member

    One thing you need to do before you release the stone is to give it a slight flick of the wrist. This in turn gives the stone a rotational motion, a gyroscopic effect. Also, the stone has to be relatively flat, almost pancake or ellipsoid in cross section to have as much bounce as possible,
     

  15. Frosty

    Frosty Previous Member

    For petes sake --old sailors would Bounce cannon balls across the ocean surface to get further, It does not need a flick of any wrist or Gyroscopic control.


    Thats just what you tell kids so they cant do it and it makes you look good.


    Look on You tube at the guy that rides a mortorcycle over water, hes going about 100KM and he can get over a river.

    Try barefoot skiing, over 40 MPH you can not enter the water you just keep bouncing, How do I know this?
     
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