Australia's Science Forum

Hi All,
I have purchased a pump to use with my bell jar to demonstate how sound cannot exist in a vacuum. Can someone please tell me if it is okay to run the pump at maximum for prolonged periods of time? Is there any possibility that items in the vacuum can be damaged while in the vacuum and/or when air is allowed back in?
Just want to know if there are any possible dangers I should be on the lookout for when using it.
jen

Your pump should be OK
But when I set this up sound did not stop because bell was silling on base and sound travelled through solid media ie bench I suspended bell from cotton from top of jar and got a better result

Thanks Ocker,
special thanks for the tip about suspending the bell
Cheers
jen

Hi Jen1,
I have found with our set up to always, always, always disconnect your vacuum pump from the jar when you have completed the prac. I can honestly say I have cleaned our bell jar that many times now because the oil from the pump eventually works it's way into it if left connected. Darn, if I don't hate doing that job! Oh, and someone suggested in another post that it is easier to listen for when they can hear the bell once the pump is turned off and not try to hear the bell (or not hear the bell in this case) over the sound of the vacuum pump.
Hope this helps,
Lou P.

Hey Loopy! that's a great idea about evacuating bell then listening to bell get louder as air restored, the simple ideas are always the best

Hi All
I have had a teacher use mobile phones in the bell jar the students love it! And I have sealed my bell jar with plasticine as it was sealed with vasoline and it was so messy.
Maureen

Hi Maureen,
Love the idea of sealing with plasticene, the grease I have been using is pretty mucky.
There is also another thread on this topic that gives some good ideas on using the bell jar, I recommend everyone revisit it.
I borrowed a metronome from the music teacher and this works wonderfully, as it can emit a really loud noise indefinitely. As it was her personal metronome I was a bit worried about any effects of putting it in a vacuum may be but it seems to have survived ok.
cheers
jen