Q:

Tricks for opening very tight jars

What are some tricks for opening seemingly impossible-to-open glass jars, like the one pictured below?

ATTEMPT: I have tried twisting as hard as I can, but clearly that hasn't worked so far. I have also tried twisting with a shirt to improve my grip. And I've tried using a knife to loosen the lid, but that also rarely helps.

A:

Usually jars with stiff lids are fresh from the store and have been packed with the contents under lower pressure than the outside air i.e a vacuum.  This pressure difference can increase the resistance presented by the thread and can make opening a jar for the first time difficult.
This approach that can be taken if a little damage to the lid is acceptable and requires only tools that are readily available in most kitchens.

Take a small tool like a butter knife or spoon.
Tilt the jar so that the seam between the jar and the lid is accessible.
Insert the tip of the tool into the seam.
Gently leaver the tool until it lifts the lid back from the jar, breaking the seal and allowing the pressure to equalize.
Now that the seal has been released it should be easy to twist the lid off normally.

With a little practice and a light touch it is possible to release the seal without permanently changing the shape of the lid.  I am happy enough keeping any food remaining in these jars if refrigerated but would avoid reusing the jar for projects with sterile requirements like making jam or preserves.

A:

You can wear rubber gloves and open it; usually, the extra grip helps.
Run hot water over the lid. The heat will make the lid expand temporarily and it'll be easier to open. 
Put the lid on hot water (works as the above method)
Hold the jar horizontally and slap the lid

A:

First, make sure the jar (and lid) are clean. A dusty jar can make it hard to maintain a firm grip. Then make sure your hands are clean, for the same reason.
If your hands are too dry, you may also struggle to maintain a firm grip. That said, you don't want them to be wet (or covered in grease / lotion / corn husker's friend) either - if rubbing your hands together feels rough, cup them and breathe into them - the moisture in your breath should suffice to let your skin grip the (clean) surface.
Make sure you're not using your wrists to break the seal. That's a good way to hurt your wrists, but a bad way to put any real force on the lid. Keep your wrists straight and use your arms to apply force to the jar and lid.
Finally, if you find that your hands are too weak to grip the lid firmly, invest in a couple of cheap hand grips.

