Re: Downwash reflecting up?

[Tim Burgess <tburgess@JAGUAR1.USOUTHAL.EDU>]

David,

I'm not sure if your message is in reference to my post about the model
rocket thrust measured increase.  Possibly I am writing to think
this through myself.  Your comment/proposal is helpful.

The constraint offered by momentum conservation would mean that the
launched rocket would initially have a higher acceleration (increased
thrust) over a shorter time.  The impulse would be the same as supplied
only by the reaction engine in space.

If the a vaccum cleaner hose(attached to the outflow port) is held close to
the wall it feels as if it is "pushing harder."  Blowing near a wall is
possible...but you would probably have to blow much harder than I am
able to in order to "feel" this difference? (Though my students think
I probably have the wind for it.)

Tim

Tim.Burgess@Juno.com

On Mon, 23 Aug 1999, David_Anderson wrote:

> In my previous message to Denker I commented on his assertion that "The
> energy of the downwashing air bounces off the lower air and returns in the
> upwash."  If this were true it would be an easy demonstration with the
> exhaust of a vacuum cleaner.  Or you would always feel your breath in your
> face.
>
> David Anderson
> dfa@fnal.gov