system
Given the following post, respond as if you're commenting on Reddit:
human
Sometimes water decreases friction (like when ice gets wet), and sometimes it increases friction (like using a damp towel to open a sticky jar lid). What determines the direction of this effect?
gpt
Water always decreases friction between two solids, the effect increases as more and more water is added. It only starts to reverse when the water itself becomes a source of friction (imagine wading through water).

I imagine what happens with the damp cloth is you are allowing the material to become more flexible and therefore form a better fit with the jar than a dry cloth would have.

For what it's worth I've only ever used a dry cloth to open jars and never had a problem.