ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related institutions.
*****************************************************************************
A number of years back, when I was doing a range of these sorts of
demos, I found a very nice alternative (extension) to the drop bouncing
balls into LN2.
If you start with a table tennis/superball sized ball of silly putty.
Make it as round as possible.
Drop it gently into the LN2 ( not suspended on a loop, as the ball will
flatten before it cools).
After it has got nicely cold, take it out. Drop it on a very hard
surface ( solid table, concrete paving slab), from about a foot or 2.
Initially it will sound and behave like a small stone ( i.e. it sounds
brittle, and bounces like a stone) Keep picking it up and dropping it in
quick sucsession. Depending on how cold you got the ball, after about 30
sec/ 1 min you'll drop the ball, and it will land, make no sound, and
sit on the concrete ( no bounce at all). It will do this for a few
drops. After that it will start to regain its usual silly putty bounce.
What is happening is as it thaws a little, a thin SKIN of
warmer/flexible silly putty will cover a ball of still solid inflexible
silly putty. When it lands, the thin layer is pinched between the core
and the deck. This creates enourmous stress, sufficient for the thin
skin to move, absorbing the energy. As it warms further the flexible
skin gets thick enough, so the stress is reduced to the point where it
can flex elastically, and provide a bounce.
Not necessarily a demo ( or explaination) for the under 5's but A nice
extension for some of the older audiences.
Hope this helps.
Stuart Kohlhagen
Manager Research and Development
Questacon
The National Science and Technology Centre.
-----Original Message-----
From: Informal Science Education Network
[mailto:[log in to unmask]] On Behalf Of Jane Snell Copes
Sent: Tuesday, 22 July 2008 9:57 AM
To: [log in to unmask]
Subject: Re: Bouncing balls for liquid nitrogen demonstration
ISEN-ASTC-L is a service of the Association of Science-Technology
Centers Incorporated, a worldwide network of science museums and related
institutions.
************************************************************************
*****
I always "follow" the frozen ball with my gloved hand so all the pieces
are under my glove. Hold the ball in your upturned, gloved hand, turn
it over, and smash it onto a hard surface like a ceramic tile. That way
no shards can get to the audience. Racquet balls work fine when
demolished in that way. Be sure the ball is in the liquid nitrogen for
at least 5 minutes. Jane
>ISEN-ASTC-L is a service of the Association of Science-Technology
>Centers Incorporated, a worldwide network of science museums and
related institutions.
>***********************************************************************
>******
>
>David,
>
>We used to use racquetballs but recently found that they survived too
>well and didn't always shatter when dropped. They may have changed the
>composition but I'm no
--
Jane Snell Copes Science Outside the Box
www.scienceoutsidethebox.com [updated 24 Feb 08] 651-357-3316
(cell)
Science Outside the Box is a tiny business that celebrates the scientist
in every one of us. I am a writer and teacher, and I have fun with
science every single day. I'm especially fond of designing classes and
science magic shows for kids and parents.
Science questions? Ask Professor Sepoc:
[log in to unmask]
"To be an inventor, you need a good imagination and a big pile of junk."
Edison
***********************************************************************
For information about the Association of Science-Technology Centers and
the Informal Science Education Network please visit www.astc.org.
Check out the latest case studies and reviews on ExhibitFiles at
www.exhibitfiles.org.
The ISEN-ASTC-L email list is powered by LISTSERVR software from L-Soft.
To learn more, visit http://www.lsoft.com/LISTSERV-powered.html.
To remove your e-mail address from the ISEN-ASTC-L list, send the
message SIGNOFF ISEN-ASTC-L in the BODY of a message to
[log in to unmask]
Classification: UNCLASSIFIED
***********************************************************************
For information about the Association of Science-Technology Centers and the Informal Science Education Network please visit www.astc.org.
Check out the latest case studies and reviews on ExhibitFiles at www.exhibitfiles.org.
The ISEN-ASTC-L email list is powered by LISTSERVR software from L-Soft. To learn more, visit
http://www.lsoft.com/LISTSERV-powered.html.
To remove your e-mail address from the ISEN-ASTC-L list, send the
message SIGNOFF ISEN-ASTC-L in the BODY of a message to
[log in to unmask]
|
