Vacuum appears to exert force on objects and molecules, since they immediately and powerfully move toward the vacuum once allowed. For example, a jar sealed with vacuum seems to pull the lid toward it, or pull air into it once the vacuum is released.
However, all that happens is molecules moving where they can move, where they have space to move into. In gas particles barely have any effect on one another (besides collisions, gravity or electric forces are negligible). All that happens when molecules move into a vacuum quickly is that the movement is in a single direction. Normally, in an average density space, particles move in all direction, creating an even pressure in all directions and a net 0 movement of the particles (more or less). However, with vacuum, every particle enters into it - nothing moves out of it, creating a very distinct sense of movement. In fact the empty space does not exert any force on the molecules - it is just normal movement except there is nothing to balance it.
What about the jar? How could I explain the fact that the lid sticks to the jar so powerfully if the vacuum exerts no actual physical force?
Like so: The lid is actually pushed by the particles outside the jar. The inside of the jar can simply offer nothing to balance it, which is why the lid is pushed onto the jar so powerfully.