1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Water Friction

  1. Jan 15, 2006 #1
    In my current scenario, I have something that was dropped from above water. I have found the theoretical acceleration of the object when it is under water (it had entered the water with some initial downward velocity) already from boyancy - weight = ma. However, in reality that acceleration is going to be smaller because of water friction. How do I take into account water friction? I know it can't be u*N which is what friction is on land.

    Thanks
     
  2. jcsd
  3. Jan 15, 2006 #2

    Pyrrhus

    User Avatar
    Homework Helper

    Try This link(it has a reasonable explanation). Just remember the problem with drag in a fluid is not as easy as you might think.
     
  4. Jan 15, 2006 #3
    Thanks for the link. How can I use the value of drag though? What equation can I use to then find out the increase in time drag creates over an ideal fluid or the lessening in velocity?
     
  5. Jan 15, 2006 #4

    Pyrrhus

    User Avatar
    Homework Helper

    Well for all purposes you can use [itex] F_{drag} = C_{drag} \frac{\rho v^{2}}{2} A [/itex] as long as you keep small speeds, therefore there will be a small Reynolds number (laminar flow). A is surface area, and [itex] C_{drag} = \frac{24}{N_{reynolds}} [/itex] in this case.
     
    Last edited: Jan 15, 2006
  6. Jan 15, 2006 #5
    Thanks again. I'm assume that the best way to find the F drag with a changing velocity is to take the average and use that as v, right?
     
  7. Jan 15, 2006 #6

    Pyrrhus

    User Avatar
    Homework Helper

    Well it depends on your approach. Do you want a variable or constant acceleration?, if its the former then you'll need to solve the differential equation, for the later you could use the average velocity.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Water Friction
  1. Friction ? (Replies: 6)

Loading...