That’s when I bang on the lid edge with a hard object to break the seal.
I use a screwdriver.
If that does not help, for smaller jars I also use adjustable pliers, for bigger ones a large workshop vise.
No special tools needed.
I just use a bottle opener, works the same way, and probably less liable to accidental stabbings than a screwdriver (been there, done that).
I usually solve the vaccum seal problem by wedging a butter knife under the edge of the lid and slightly twisting the knife. Usually that’ll lift the side of the lid enough to break the seal, sometimes you need to try a couple of different spots on the lid but it works pretty nicely for me.
You must not push the screwdriver. Place it into the groove, twist. If you risk stabbing yourself, you’re doing it wrong or use a too thick screwdriver (which is also doing it wrong).
Yeah, I probably have been doing it wrong, although I have more bottle openers in the kitchen than screwdrivers 
I have one of these and love it, although it doesn’t work on things like Mason jars that don’t have a lip you can slide it under. For those I prefer a swing-a-way.
A vacuum seal doesn’t “pull” the lid closed - the pressure differential of the air on the outside is pushing it closed. And yes, this is a great tool - it’s essential if you do any home canning.
Bonus: much smaller chance of breaking the glass. Twisting a screwdriver under the lid? Yikes!
I work with my hands, all day. I encounter a jar I (almost) can’t open bare handed only about once every two years. Usually heating up the lid with warm water is all it takes, or eliminating the hand slipping, by some grippy material or washing my hands.
/fifteen years of judo also helps.
I’d say both the formulations count as correct. Depends on what side of the lid you look at.
I never cracked a glass this way. You have to be gentle. If the lid doesn’t want to give way at the given point, try next to it. “Talk” with it and let it tell you where the right point is.
Every gadget ever made. I swear you guys must have kitchens the size of the Taj Mahal.
When my hand strength alone or with a grippy pot holder isn’t enough, I usually whack the edge of the lid with the back edge of a table knife – not the serrated edge, the other edge. A couple whacks break the vacuum and the lid pops right off. This does put dents in the edge of the lid, but that’s never been a problem for me.
Reliable, easy-to-use jar openers are important for people with limited dexterity, though – injury, arthritis, nervous-system damage, etc. It would stink to have to ask for help on every jar.
A rubber band is my favourite, very rarely fails. Then it’s on to oil filter wrenches.
I just run the lid under hot water for a few seconds. The metal expands slightly and pop, easy open.
Yup. Taught my kids to use a bottle opener when they were in preschool. Easy peasy, and everyone already has one of those.
I grew up with one of those! It was a weird rose-gold color.
Well, I’d judge the push perspective as preferable if only on the grounds that both pushing and pulling require agency. I can see airy molecules being an agency for push, but I don’t see anything physical doing any pulling. I’d not recommend testing the hypothesis that it’s the earth doing the pulling via gravity as you’ll get very wet when you try to falsify that hypothesis.
That’s about $6 too expensive, I’m afraid. Anything that you can wedge into the lid can be used to easily break the vacuum seal. Like, say, a can-opener, bread knife or a screwdriver, and probably you have one of those already. Whatever, so long as you don’t waste time with that stupid hot-water approach…
From physics perspective, you’re formally right. From engineering perspective there’s no real difference.
There is no gravity. Earth sucks.
