Opening a Jar: Physics Behind Jar Lid's Resistance to Opening

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In summary, the conversation revolved around the difficulty in opening a jar of sauce and the solution being to shake the jar to release the stiction between the lid and the sauce. The phenomenon was explained to be caused by a layer of air between the lid and the sauce that was no longer present after shaking. The physics behind this was discussed and it was suggested that the way one holds the lid and applies pressure can also affect the ease of opening.
  • #1
Gondur
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Hello,
I bought a jar of sauce today.
I tried to open the top, but I couldn't - it wouldn't budge at all.
Then I shook the jar - so the sauce inside moved around.
I tried again and I effortless opened the jar.

Now - this got me thinking, why when I shook the jar did it open easily?
prior to shaking, the jar would have been sitting for days on a shelf.
There was a layer of air between the lid and the sauce.
after shaking, this layer of air mixed with the sauce and was no longer present.
so, perhaps it was the layer of air between the lid and the sauce that made the lid impossible for me to open?

Could someone explain the physics behind this phenomenon I encountered?
Thank you.
 
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  • #2
Hot hands?
 
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Likes russ_watters and jerromyjon
  • #3
Silly question but did you turn the lid the same way both times?
 
  • #4
Perhaps there was a crystallised region between the lid and the top of the jar - or maybe in the beginning of the thread. When you shook up the liquid, it dissolved the crystals and released the stiction.
 
  • #5
Gondur said:
why when I shook the jar did it open easily?
I've had the same experience on occasion -- and am still looking for a definitive answer. Any definitive answerers out there to satisfy irrelevant curiousity?:wink:
 
Last edited:
  • #6
Tom.G said:
Any definitive answerers out there to satisfy irrelevant curiousity?
Yes.
It has everything to do with the way you hold the lid. If you apply the grip pressure equally to all fingers and space the fingers equally around the lid it is often very easy to undo the lid because you are not distorting the lid. As you apply increasing torque to the lid, allow a very slight slip to your fingers, so they gradually move around the lid. That will usually find a sweet spot where the lid will release, if not, the cyclic massage will crack the stiction between container and lid.

If you can find an aluminium container with an aluminium screw top lid, you can practice the delicate art of removing lids. Most people will grip the lid at two opposing points and squeeze hard to get a grip, which will lock the lid even if it was not tight and rattled before they started.
 
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Likes Tom.G

What causes a jar lid to be difficult to open?

There are several factors that can contribute to a jar lid's resistance to opening. The most common cause is the seal created by the vacuum inside the jar, which can make it difficult to break the initial seal and release the lid. Additionally, the friction between the lid and the jar's threads can also make it harder to open.

Why does running the jar lid under hot water make it easier to open?

When you run a jar lid under hot water, you are essentially heating up the air inside the jar. This causes the air to expand and create pressure, which can help break the seal and make it easier to open the lid. The heat can also help soften any dried food or liquid that may be causing the lid to stick to the jar.

How does using a rubber grip or towel help with opening a jar?

Using a rubber grip or towel provides additional friction and grip, which can help you get a better hold on the lid and twist it open. This can be especially helpful if your hands are wet or if the jar is slippery due to condensation or oil.

Is there a difference between opening a glass jar and a plastic jar?

The physics behind opening a glass jar and a plastic jar are essentially the same. However, glass jars tend to have tighter seals and may be more difficult to open due to their rigidity. Plastic jars, on the other hand, may be easier to open because they are more flexible and can be squeezed to break the seal.

How can I prevent a jar lid from getting stuck in the first place?

To prevent a jar lid from getting stuck, make sure to avoid over-tightening the lid when closing the jar. This can create a stronger seal, making it harder to open later. You can also try wiping the threads of the jar and the lid before closing to remove any food or liquid that may cause the lid to stick. Additionally, using a jar opener or tapping the lid with a spoon can help break the seal before attempting to twist it open.

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