This is a great video about all the things that make jump scares stupid yet highly effective. I really hate jump scares because I know for a fact that they don't quite work without any sound which means from a purely visual perspective, they aren't that interesting.
While jump scares are often incredibly quick, a few movies recently have combined the use of sudden sound with slow movement to make the jump scare even more frightening. One great example recently of this is the "Face of Fire" moment in Insidious. I've embedded the video below if you want to see it. The build-up is intense.