The next time that you are struggling to open a new jam jar (or a jar of marmalade, or pickle, or whatever takes your fancy, of course) grab a teaspoon. With the back of the spoon, give the rim of the lid a few strong taps. The lid should come off easy as anything.
My mother assures me she has used this technique to open jars that had previously defeated the strongest of men.
I've not done any scientific research, but it seems to work!
