Now, London dispersion forces are the weakest because these exist only for a moment in time. So at one moment they exist, and another moment they don't exist, and a third moment, they exist once again. And so that's why they're the weakest types. But once again, if we have many of these molecules in close proximity, Vanderwald forces, lunaspersion forces begin to play a very substantial role in holding the molecule together, as we'll see in the structure of DNA. So London dispersion forces are forces that exist because these electrons fluctuate over time. So the electron density around atoms is not static, but rather fluctuates with time.