Re: weight of a bird in a cage

[brian whatcott <inet@INTELLISYS.NET>]

At 12:09 9/6/99 -0400, Lois wrote:

[Brian]
> > It is however unclear how far an average grain needs to fall before
> > reaching terminal velocity.
>
>
> But I thought it didn't matter what was falling unless there was
> appreciable drag. Guess I'm unclear on terminal velocity.
> Someone give me the short version?
>
> Dr. Lois Breur Krause

['short' takes too long, here is the quick 'extended' version, sorry!]

If I drop a pellet from the top of an evacuated column, its weight
no longer registers on the scale supporting the container,
until it hits the base, whereupon it unloads its
accumulated momentum with an impulse.

If I drop a pellet in a liquid filled column, I find that the
 pellet's weight is indicated very soon during the course of its
descent.
The liquid evidently supports the pellet's weight, and it descends
at a constant or terminal velocity.

   A recreational parachute jumper reports a similar effect:
her speed builds to about 120 mph at which point she is cushioned
on air at her terminal velocity.

A long hour glass when turned, has sand particles accelerating to
some maximal speed. We can be quite certain that this speed is well
less than 120 mph. But we ( or rather I) am unaware of this speed,
for the grain size commonly used in hour glasses.

 Turning the question on its head, you might consider establishing
the terminal speed of hour glass sand like this:
 place a very long tube on a scale and weigh it, together with a
cup of sand suspended at the top.
 Arrange an electrical means to release the sand, and record a time
history of the total weight measured by the scales.

Before release, the weight is tube plus sand.
 At release, the weight becomes tube alone.
 In a short while, the weight increases towards a terminal value of
 tube plus sand. This time is a measure of the terminal velocity
 of the sand particles, at which time, the sand's weight is fully
supported by air. If the tube is long enough, the terminal velocity
occurs before impact.

I hope this helps.

brian whatcott <inet@intellisys.net>
Altus OK