Monday, January 29, 2007

Post-PTSOS2 note: Leidenball video clips

This is the clip I showed of the very hot brass ball immersed in 75degC water. The envelope of water vapor around the ball is the result of the Leidenfrost effect. The poor thermal conductivity of the vapor allows the ball to remain hot for a surprisingly long time.


I shot this one in class with a highly vocal and somewhat roudy group of Advanced Placement Physics students. I didn't tell them what was going to happen beforehand, but you can hear one of them say, "Leidenfrost, eat your heart out." They had seen Jearl Walker's Leidenfrost effect video one calendar year earlier.


While trying to film the effect, I ran through several takes. Not all of them went according to plan.

Still, there's a lesson to be had here. How is it that the ball could sit in the flame for ten minutes only liberate itself from the rod stem seconds after being immersed in the water?

Here's the one I shot of demo discoverer, Paul Robinson, showing the Leidenball at the workshop.


Technical note to Mac OS X users hoping to upload clips to YouTube. If you upload QuickTime files to YouTube, the sound will lag behind the video by a second or two. Be sure to convert your clips to MP4 format for uploading to YouTube. Apple's QuickTime Pro ($29) will do this.

6 comments:

Anonymous said...

YES! I can finally show these clips to my friends. Much safer than risking third degree burns by trying it myself.

Doug Baird said...

Very cool, er, hot! There always some new concept I haven't heard of. Thanks for bringing me another.
Doug

Anonymous said...

I'm a Mac OS X user. When I save as an mp4, the audio syncs up, but I lose TONS of quality on the video end. Any suggestions?

ozymandias1 said...

This is wonderful. I was taking a break from correcting papers here in Dublin on a Saturday evening and treated myself to a half hour's worth of 'surfing'. All clips are amazing. Thanks for posting.

Hope it's okay if I add you to my blogroll?

Regards,

Noel

Darnell Bardsmoth said...

Its is quite a beautiful thing. At what temperature was the brass probe? Or is it not important to know specifically?

Dean Baird said...

The brass ball was heated in the flame of a Bunsen burner operating on natural gas.