In mechanics, a force is that which causes a change in velocity or, if you prefer, that which causes an acceleration. When more than one force acts on an object it is the net force that is important. Since force is a vector quantity, use geometry instead of arithmetic when combining forces.
Quick Answer. A crawling sensation felt on the skin may be caused by a condition called morgellons, according to WebMD. Common symptoms of morgellons include feeling like bugs are crawling on the skin, burning, itching and stinging sensations. In some cases skin sores may appear as well.
So the worm wants to get out, and here's where it gets even weirder. The worm burrows to the surface of the skin and creates a blister, and causes a burning sensation. It does this on purpose, because the worm has figured out that a burning feeling in a limb makes humans want to dunk it in water.