Mondo Knows Facts
A jar lid button shows if the seal held
Cooling contents pull the lid down, and a released button means air got in Jars are filled hot and capped, and as the contents cool the trapped air contracts, so the internal pressure drops and the lid is pulled concave. That vacuum holds the lid tight and makes the safety button sit down. If the button can be pressed and clicks, the seal has failed and the contents should not be trusted. It sits in Mondo's everyday life collection, one of 200 facts that each trace back to the reference below.
Where this comes from
Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.
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Aluminium foil shiny sides result from rolling metal sheets togetherDouble rolling foil sheets creates glossy outer sides and matte inner surfacesGas hobs stay lit thanks to a thermocoupleThe flame generates a small voltage that holds the gas valve openAn oven thermostat senses heat through a sealed capillaryA fluid filled probe expands and switches the element on and off in cyclesFrost free freezers melt their own iceA small heater briefly warms the evaporator so frost drops away unseenFridge doors seal with a flexible magnetic stripA soft PVC gasket holds a magnet that grips the steel cabinet frameCling film sticks through static and close contactPeeling the roll strips electrons, so the sheet clings to almost any surface
🧭 Everyday Lifefact 195 of 200
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Tags: packaging, preserving, kitchen
A jar lid button shows if the seal held: the short answers
- Where does this come from, and can I check it?
- Cooling contents pull the lid down, and a released button means air got in. The figure is taken from US Department of Agriculture, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
- Is this really a everyday life fact?
- Yes. It sits on the Everyday Life shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
- What else can I read about it?
- The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.