Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
ar.
I tried to send a reply that was rejected - I forgot that one can't
attach pictures to a Phys-L posting. Here is my original message,
without the pictures.
We use a "liquid accelerometer" made from a (clean) peanut butter j=
It was a giveaway several years ago at a meeting of ISPP, one of ou=r
local teacher alliances. A gasket is made from a plastic coffee canarm's
cover. (Pictures 1 and 2) Have a student hold the accelerometer at =
length (Picture 3), then step forward. (Picture 4) The floating bal=l
moves forward. Ask "What was the direction of your acceleration?" H=ave
the student walk, then stop abruptly - again the floating ball poin=ts in
the direction of the acceleration. Then have the student rotate, st=ill
holding the accelerometer with arms extended, and all will see the =ball
pointing inward. (Picture 5, with the device on a Pasco rotatingsome
platform) Physics Cinema Classics, in the section on rotation, has =
footage of a similar device: "Acceleration of air table puck andOn
automobile."
I will be glad to send pictures to anyone interested. Contact me by
e-mail.
John Milton
De Paul University
Chicago, IL
-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu]=
Behalf Of Karl Trappee
Sent: Friday, January 27, 2006 2:26 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: rotating stuff (was: telescope mirrors)
Hey, Denker...you ought to know how *cheap* I am!
I use the string to tie the beaker down so it doesn't fly off, but
then the string slips down while in motion, so I duct tape it to th=
beaker...Your annulus rig is much cleaner. It does need to be thickt:
enough that a shift in CofM doesn't let the beaker tip.
Good point about how cheap turntables are nowdays. Add to your lis=
"comparing SHM". Drill a hole for an upright stick on the turntabl=e
or make a magnetic support if the turntable is out of steel.. Add =a
ball on top of the stick for visibility. Set the turntable to one =of
its RPM values. Mount above this either a ring stand with a pendul=um
adjusted to have the corresponding frequency to the revolution or ae
SHM spring with the correct mass. Voila, direct observation of
equivalence of rotation with spring with pendulum. You can shadow
project with a bright point light source and observe the coincident
location of the shadows on the wall. Have the students calculate th=
correct length for the string or the correct mass for the SHM sprin=g
(find k first).its
If you have the option, getting a turntable that will run while on =
side will make the SHM of spring comparison easier. Alas, most areing
driven with an idler wheel, that relies on the turntable platter be=
horizontal.l
Quoting John Denker <jsd@AV8N.COM>:
Karl Trappe wrote:
Tie a beaker to a lazy susan turntable (or on your rotating stoo=
ater,apparatus) using string and duct tape. Partially fill it with w=
l notspin it and observe. If you move it off center, the results wil=
ure abe symmetric, of course.
For an additional application while you have the apparatus: sec=
atsstring to the bottom center of the beaker (epoxy a swivel to the
bottom). tie a cork/styrofoam ball to the string so that it flo=
se afrom the bottom. Next hang a weight on a string from the top (u=
vestrp of thin aluminum with a hole in it).Set this beaker far off
center and rotate the lazy susan slowly. The heavy ball will mo=
iumoutward and the floating ball will move inwardmimmicking the hel=
tingballon vs the air filled balloon in an accelerating and decelera=
...car.
Very nice. Thanks.
Some tangential remarks and refimements:
lazy susan turntable
You can still get _record player_ turntables ($10 on ebay) (also
garage sales sometimes) which are absolutely ideal for this demo =
onand for many other demos, including e.g. bouncing a laser off a
tuning fork (or loudspeaker) to draw the acoustic waveform graph =
pedthe wall......
using string and duct tape
I don't understand how "string" enters into it.
If you really want to get fancy, make an _annulus_ out of light
gauge plywood. The hole in the middle is just the right size to
hold the beaker. The outer rim of the annulus is easily duct-ta=
_______________________________________________to the turntable.