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Re: timing data for falling objects



From: Hugh Haskell [mailto:hhaskell@MINDSPRING.COM]
Sent: Saturday, July 06, 2002 12:16 AM

Maybe I'm being too simplistic, but it seems to me that what Robert
is looking for (Robert can speak for himself better than I, but I'll
toss in my $0.02 worth anyway), is data from a free-falling object
that covers enough time to show the effects of air resistance,
perhaps even terminal velocity.

Yes, I am looking for data from an object that has a ~ 9.8 m/s2 downward for
short distances but deviates from this for longer distances. It need not
reach terminal velocity.

I suspect that it might be difficult
to come by, but how about generating some of your own, by videotaping
an object (a basketball, say, being dropped from the top of a four-
or five-story building.

I thought someone had already done this and could simply pass on their data
to me. I don't have time right now to do the experiment myself but, seeing
no one volunteering the data, I'll use my quick-and-dirty method of dropping
a ball down a stairwell.

From: John Mallinckrodt [mailto:ajm@CSUPOMONA.EDU]
Sent: Saturday, July 06, 2002 11:52 AM

I have to agree with Hugh here. If the purpose is to determine the
velocity-dependence of the drag force--as I suspect it is--it will be
difficult to come by data that is accurate enough.

I do not intend to use the data to obtain the drag force. I just want some
"real" data to illustrate that ignoring air resistance is okay for short
distances. I don't want to make up or simulate data.

There was a
thread on this in December 1997 that may be reviewed at

http://lists.nau.edu/cgi-bin/wa?A1=ind9712&L=phys-l&D=0#95

(BTW, the review is made needlessly difficult due to the fact that
various contributors used the subject headings "air resistance", "Air
resistance", and "Air Resistance" which are all considered to be
different threads by the archiving software.)

Thanks for the lead - I hadn't thought of searching for "air resistance". I
checked it out but only a portion of Ludwik's data is included.

Thanks to all who responded.
____________________________________________
Robert Cohen; rcohen@po-box.esu.edu; 570-422-3428; http://www.esu.edu/~bbq
Physics, East Stroudsburg Univ., E. Stroudsburg, PA 18301