Cohesion is how strongly a substance holds itself together, and viscosity has been described as the substance's internal friction. Viscosity has mostly been explained to me via allusions to substances that have a high viscosity, like syrup. To me, it seems intuitive that viscosity would be the emergent phenomenon resulting from molecules being strongly connected to each other. I mean, it makes sense; it's harder to pull your hand through the substance because the substance internal connectivity is giving you more resistance. However, that's apparently not the case, since cohesion is the word for the collective strenght of the molecular bonds, and viscosity is something else. Also, water has pretty strong molecular bonds, dipole hydrogen bonds, but isn't very viscous.

So, I created this hypothesis, and I'd like to see if it is true or not. Substances consisting of non-polar molecules are more viscous, because the molecules are held together by London Dispersion Forces (LDF), instead of dipole-dipole bonds. Now, LDF works via temporary polarization, which sometimes happens spontaneously due to the random movement of electrons, but usually happens through induction via a dipole nearby (which can be temporary or permanent). Basically, there is created a charge imbalance across the molecule or atom, because electrons do not stand still. This charge imbalance makes it a temporary dipole, which will make it e.g. negative pole move towards the nearest temporary dipole's positive pole.

These temporary dipoles are being made all the time, very quickly, which creates an ocean of chaotically pullinh and pushing electrostatic forces, which creates a lot of movement. All that movement increase the inertia of the molecules, which increases the energy needed to displace them. So, when you pull your hand through this substance, you don't just have to overcome the inertia created by the molecules' mass, but also the intertia created by their constant movement.

Is this hypothesis true or close to the truth?

  • $\begingroup$ Why do you think the inertia increases? Are you imagining the molecules are moving so fast that relativistic effects come in to play? $\endgroup$
    – Ben51
    Feb 8, 2021 at 13:53
  • $\begingroup$ @Ben51 My understanding is that an object's intertia increases when it is in motion. It has a momentum, pulling it in one direction; if one wants to pull it in another direction, one must overcome its mass AND its momentum that is pulling it in a different direction. Is this incorrect? $\endgroup$
    – A. Kvåle
    Feb 8, 2021 at 14:00
  • $\begingroup$ Yes, that is incorrect. $\endgroup$
    – Ben51
    Feb 8, 2021 at 14:01
  • $\begingroup$ one must overcome its mass AND its momentum that is pulling it in a different direction. Is this incorrect? That's nonsense, sheer and utter. $\endgroup$
    – Gert
    Feb 8, 2021 at 14:05
  • $\begingroup$ @Gert I see, my hypothesis is then probably quite wrong since its is based on this faulty understanding. $\endgroup$
    – A. Kvåle
    Feb 8, 2021 at 14:10


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.