cool it. When molecules are cooled they compress.
Often, lids are made of metals which are great conductors of electromagnetic waves (including heat). When warm water is applied to a "difficult" lid, excitement of the atoms in the metal occurs (very slight) which causes a slight expansion. This expansion helps the lid to be moved from it's grip on the jar or bottle. This is also found in plastics. Although not through expansions. The heat from the warm water literally softens the plastic.
Using hot water to open a metal jar lid helps to expand the metal, making it easier to twist open the jar. The heat from the hot water causes the metal to expand while the glass of the jar remains relatively unaffected, creating a temperature difference that helps to loosen the lid.
Heat causes the metal to expand, thus breaking the seal.
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Running the jar lid under hot water causes the metal to expand slightly, making it easier to unscrew. The heat helps to break the seal created by the contents of the jar, allowing you to open it more easily.
Keep it in a tightly closed jar. In a cool place it should be fine.
When you heat the jar, the glass expands only slightly while the metal expands much more. This is governed by the coefficient of expansion for the substance. The greater the coefficient of expansion, the more the substance expands. Since metal generally has a much higher coefficient of expansion, the lid of the jar will get bigger while the jar only expands slightly. That makes everything a little looser, which makes it much easier to open the jar.
You can make an Jar Airtight by hooking up a machine that pulls the air out of it and selas the top or you can place the jar into boiling water to heat the contents of the jar. as the contents cool it will pull the lid tight on the jar making an air tight seal.
When hot liquid is added to a jar, it heats the air trapped inside the jar. As the air expands, it creates pressure which pushes against the metal lid, causing it to buckle or dent. This is due to the difference in pressure between the inside and outside of the jar.
Heat should not cause a jar to seal more tightly. There is an excellent reason for this, and it lies in the physics of the coefficient of thermal expansion (CTE) of materials. If you run hot water on the (stuck) lid of a glass jar, the jar will undergo only a little thermal expansion. The metal lid however, will expand more than the glass, and will do it more rapidly, too. Running a jar under a bit of hot water should act to loosen the lid instead of tighten it. The CTE of metals is higher than that of glass, and the lid, because it is metal, will also have a higher rate of thermal conductivity than the glass. Thermal energy will move through it more quickly to change its size. This double whammy should not cause the lid of the jar to tighten. If the lid is still stuck, then insufficient force has been applied to it to get it unstuck. Increased care is indicated as efforts are redoubled to remove the lid.
Heating the lid of a jar causes the metal to expand, breaking the seal between the lid and the jar. This makes it easier to open because the pressure inside the jar is released, reducing the force needed to twist the lid off.
Running hot water over a tight lid causes the metal to expand slightly and lose some of its grip on the jar, making it easier to open. The heat loosens the seal between the metal lid and the glass jar, reducing the friction and making it easier to break the seal.