Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 03/12/2007 08:18:23

Title: how the heck can i open my jar of jam?
Post by: paul.fr on 03/12/2007 08:18:23: ever had one of those jars that just will not open? Or you take one from a girl to show how strong you are, then look a fool when you still can not budge the lid?
In such cases, quite often ,a few taps on the bootom of the jar against a work surface will loosen the lid, why should that be?
Title: how the heck can i open my jar of jam?
Post by: Soul Surfer on 03/12/2007 09:10:18: The ultrasonic vibrations that you generate with the impacts will loosen up the stickyness that is stopping you unscrewing the lid.
Title: how the heck can i open my jar of jam?
Post by: syhprum on 03/12/2007 10:37:34: The easiest way is to wind sticky tape around the outer rim of the lid to give a better grip or in the case of a jar where a partial vacuum results in pressure on the lid to simply punch a hole in it (spare lids should be stockpiled)
Title: how the heck can i open my jar of jam?
Post by: lyner on 03/12/2007 22:56:00: Running hot water can work well for sugar solutions jamming the threads of a lid. It also relieves the low pressure inside.
Title: how the heck can i open my jar of jam?
Post by: JimBob on 04/12/2007 04:10:47: I just use a jar wrench.
Title: how the heck can i open my jar of jam?
Post by: SquarishTriangle on 04/12/2007 08:23:47: Turn the jar over and have a look underneath. There should be a two or more notches/indents on the rim of the lid that 'lock' the lid on. Just unlatch the notches with a little tweak of a knife, spoon or whatever you have lying around. Unscrew lid. Easy.
Title: how the heck can i open my jar of jam?
Post by: techmind on 04/12/2007 10:33:51: I don't think you'll find that the vacuum/low pressure inside many jars is a significant contributer to the difficulty of opening lids.
I have enough strength to turn the lids, but find it's not always possible to grip the lid sufficiently (tightly?) to avoid slippage. This can be a particular problem if the lid (or hand) is wet or greasy (or, I suppose, if you had extra dry skin). If you can wipe (degrease by wiping with a cloth wetted with detergent-water) the lid and dry it (and hands) thoroughly, I find it helps a lot.
Other than that, banging the bottom of the jar against a hard surface while trying to unscrew sounds promising.
Part-used jars of honey with gummed-up threads are a different matter(!)
Title: how the heck can i open my jar of jam?
Post by: syhprum on 04/12/2007 17:19:11: Quote from: SquarishTriangle on 04/12/2007 08:23:47
Turn the jar over and have a look underneath. There should be a two or more notches/indents on the rim of the lid that 'lock' the lid on. Just unlatch the notches with a little tweak of a knife, spoon or whatever you have lying around. Unscrew lid. Easy.
One should be very careful using metal tools to prise of lids, if you get tiny glass splinter's in your fingers they can cause pain and annoyance for weeks
Title: how the heck can i open my jar of jam?
Post by: SquarishTriangle on 06/12/2007 08:20:44: Quote from: syhprum on 04/12/2007 17:19:11
One should be very careful using metal tools to prise of lids, if you get tiny glass splinter's in your fingers they can cause pain and annoyance for weeks

Oooh! That sounds like something I need put on my list of things to do.
Title: how the heck can i open my jar of jam?
Post by: lyner on 06/12/2007 15:55:57: Quote
I don't think you'll find that the vacuum/low pressure inside many jars is a significant contributer to the difficulty of opening lids.
Au contraire, I would say that the pressure on the whole lid can cause a force of, say 20N against the rim. If the coefficient of (static) friction is , say, 0.2, then you have an extra tangential force of 100N to overcome. that's like lifting 10kg.
My figures are a bit ball-park but not ridiculous. Compare opening a new jar of jam- when it goes psssst, with opening it the next time. Isn't that all due to the changing pressure difference?
Title: how the heck can i open my jar of jam?
Post by: syhprum on 06/12/2007 19:59:37: The most recalcitrant lids can be removed by the following technique.
Use a pair of scissors to punch two small holes in the lid, partially open the scissors and insert each of the blades in each of the holes.
Insert a bar between the blades close to the lid (a wooden spoon does fine).
Get an assistant to hold the jar and rotate the lid taking advantage of the enhanced leverage provided by the bar.
It is as well to use borrowed scissors and wooden spoon for this purpose
Title: how the heck can i open my jar of jam?
Post by: lyner on 06/12/2007 23:01:46: You forgot the newspaper to catch the blood.
Title: how the heck can i open my jar of jam?
Post by: rosalind dna on 07/12/2007 22:26:19: just put the jam jar in some tepid water for 5 minuntes and then turn the
lid with rubber gloves on. They will give you a better grip and then you'll
have one open jar.
Title: how the heck can i open my jar of jam?
Post by: Karen W. on 07/12/2007 22:29:53: If you set the jar on the counter and give the cap a good thump with the palm of your hand, right in the middle of the jar lid, it breaks the vacuum and allows the jar to then open up upon untwisting again.
Title: how the heck can i open my jar of jam?
Post by: Karen W. on 07/12/2007 22:32:26: Quote from: rosalind dna on 07/12/2007 22:26:19
just put the jam jar in some tepid water for 5 minuntes and then turn the
lid with rubber gloves on. They will give you a better grip and then you'll
have one open jar.

This works also I have used both..BTW Welcome to the forum Rosalind. Hope you enjoy it!
Title: how the heck can i open my jar of jam?
Post by: rosalind dna on 07/12/2007 22:39:52: Thanks Karen
Title: how the heck can i open my jar of jam?
Post by: Karen W. on 07/12/2007 22:50:58: Your welcome Have fun!
Title: how the heck can i open my jar of jam?
Post by: Totty on 07/12/2007 23:42:30: My friend says that you should bang the side of the lid agaist a table of something. She showed me and it seems to work.