A friend of mine at work sent me this link that states that you can't swim in honey, and then provides an explanation as to why you can't. Since the physics stuff is over my head and my smarts are in another field, I don't know the soundness of the author's conclusion. I just thought this was an interesting topic. I know about the Mythbusters episode, but they were swimming in a syrup-like substance that didn't seem near as thick as honey. Any thoughts?
www.dedoimedo.com/.../honey.html
His entire premise seems to be that propulsion can only be achieved in turbulent flow and this is wrong. For example, an airfoil still produces lift in laminar flow. Also he's wrong about when flow becomes turbulent. The Reynolds number of 2300 he states for laminar to turbulent transition is only valid for the flow of liquid in a pipe. This is not a good analogy for a swimmer. In pipe flow, the friction that causes the boundary layer to grow, and hence eventually cause tubulence is between the liquid and the walls of the pipe. For a swimmer we need to consider the friction between the swimmers arms and legs and the water. The sides of the pool don't have anything to do with whether or not we can swim.
If you had something even more viscous than honey, then there would be a point where swimming (underwater) would be impossible. At this point, for Reynolds numbers much less than zero, we get into a regime called Stokes flow where viscous forces dominate inertial forces. Remember that we are relying on inertial forces to propel us, so when the viscous forces dominate we wouldn't be able to go anywhere. This is an entirely different issue than laminar vs. turbulent flow.
I just wasted an hour reading about all kinds of physics concepts that I have no business trying to understand. I am supposed to be writing software, not reading about the top 10 classic mistakes made in sci-fi movies, and more.
Thanks for sharing the link. Very interesting.
His entire premise seems to be that propulsion can only be achieved in turbulent flow and this is wrong. For example, an airfoil still produces lift in laminar flow. Also he's wrong about when flow becomes turbulent. The Reynolds number of 2300 he states for laminar to turbulent transition is only valid for the flow of liquid in a pipe. This is not a good analogy for a swimmer. In pipe flow, the friction that causes the boundary layer to grow, and hence eventually cause tubulence is between the liquid and the walls of the pipe. For a swimmer we need to consider the friction between the swimmers arms and legs and the water. The sides of the pool don't have anything to do with whether or not we can swim.
If you had something even more viscous than honey, then there would be a point where swimming (underwater) would be impossible. At this point, for Reynolds numbers much less than zero, we get into a regime called Stokes flow where viscous forces dominate inertial forces. Remember that we are relying on inertial forces to propel us, so when the viscous forces dominate we wouldn't be able to go anywhere. This is an entirely different issue than laminar vs. turbulent flow.
Thank you.Other problems are that he thinks the propulsive surfaces are limited to hands and feet and that the force that can be applied is related to the weight of the man which is irrelevant when floating.that's some of the problems i see without getting into the deeper physics.
