Download Modeling drag for the coffee filter

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Flight wikipedia, lookup

Transcript
Modeling drag for the coffee
filter
Dr. Fisher, 15 Sept 2010
(ref Brueningsen et al, The Physics
Teacher, 32, Oct 1994, p 439)
Some charts
A simplified view of filter movement
through air
• For low Re: the air slips around the filter
• For High Re: Filter, mass M, moves through air,
and it collides with an air molecule, mass m,
initially at rest.
• For the filter, change in momentum is
Dp = mv(2M/M+m)
• Which for M>>m, becomes ?
• Dp = 2vm
As the filter moves through air..
• It sweeps a volume, V, of air
V= AvDt where A is x-sectional area, v is velocity,
and t is time
The Mass of air swept out or displaced is r(AvDt)
• So, the average force applied to the filter due
to collisions is Fd = Dp/Dt
– Another form of Newton’s second law
• Thus, for all the air Fd = (2r(AvDt)v)/Dt
– Which means Fd = kv2
Models to test
• For low Reynolds Number, Stokes flow, we
expect Fd = kv
• And for high Re, we expect Fd = kv2
• So we should check them both to see which
model works
• If we don’t have enough data to test it, then
we can get more data!