Step-by-Step: an pump-like machine in action.

This "machine" was built in Interactive Physics (Knowledge Revolution, K-Rev).

Frame 1 - A charged molecule [A] with a strong minus (blue) is attracted to a positive part of another, larger hinge-like molecule [B].

Frame 2 - Its positive end is repelled by the other positive and this forces it into the "jaws.

Frame 3 - The structure closes. [WHY?]

Frame 4 - The molecule [A] is held tightly.

Frame 5 - The hold on the smaller molecule [C] is loosened.

Frame 6 - The smaller molecule [C] is released.

---