1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Non-linear inertia from rest seems common?

  1. Jan 2, 2015 #1
    It seems to me that there are many instances of 'initial stickiness' when you move an object. Pushing a book over a table for example might be initially hard due to adhesive forces to the table which have formed over time - a plastic coating forming some kind of seal with a varnish is the obvious example, but even without it you might even get 'bearings made of dust' lessening friction with distance, or an air bed forming as the book is moved, or perhaps hydrogen bonding formed from the humidity existent within the surfaces, all possible.

    I wondered if there was some initial stickiness due to the gyroscopic effect of electron orbitals? If so I am surprised that this hysteresis is not more commonly reported, it seems to exist more commonly that not?
  2. jcsd
  3. Jan 2, 2015 #2
    The simplest explanation would be static and kinetic friction.
    It takes more force to start an object to move, due to the higher static friction, than to keep it moving, due to the lower kinetic friction.
  4. Jan 6, 2015 #3


    User Avatar
    Homework Helper
    Gold Member

    Can that be called an 'explanation'? - it seems more a restatement to me.

    However it is known that fairly generally kinetic friction does increase at low velocities. There is a familiar example yet not often recognised because not incorporated in the theoretical things we're taught (this has an epistemological aspect). When you brake a car with a constant applied force just at the very end the friction increases a lot and you stop with an increased deceleration, I.e a jerk. Familiar yet not intellectualised so not often recognised.

    I am away from sources now, but this is in an article about friction in Scientific American in the 1970's or '80's.
  5. Jan 6, 2015 #4


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Static friction comes from a variety of things, some of which are not yet fully understood. The science behind a gecko's feet is a current area of research.
  6. Jan 6, 2015 #5
    friction is created because of the collision between atoms of two adjacent surface areas .... friction is dependent on the type of the surface area(smoothness of the area) rather than the gyroscopic motion of the electrons .it also depends on the speed of the moving surface as the collision rate increases with speed .. but the electrons can be affected because of friction as we see if we rub a stainless steel with a rough surface the outer electrons may be energized causing sparks ....
  7. Jan 7, 2015 #6
    I should read posts better.o:)

    There are several dynamic models to describe the stick-slip "jerk" friction as you mentioned, such as the earthquake model and the spring model at the nanoscale, and along with that some ideas on the physical aspects of what is occurring, such as molecular orbital overlap, which may be getting close to what the OP is referring to.
    The rarely mentioned relationship of friction with velocity is called the Stribeck effect.

    Tribology, or the study of friction and related aspects, as Fact checker mentions, not completely understood, but it has come a long way from the linear Coloumb friction model.

  8. Jan 26, 2015 #7
    Thanks for the replies. The subtlety which I was trying to address is explained as follows. If I push the gyroscope gently the gyroscope doesn't move as a static mass would? I believe that some of the energy of the spin is constantly changing the vectors of the atoms to some extent work against the push.

    So if we consider electrons some of this effect should exist unless the term 'orbital' is deceptive and that the word orbital just means a zone in which the electron may exist.
  9. Feb 8, 2015 #8
    Okay I found out that the term orbitals is deceptive and is, I suppose, a left over term from Bohr's original idea of atomic structure.

    But I am confused if nuclei spin then they must add some gyroscopic inertia too? If so why are substances not heavier when they are hotter, as I assume for example in a gas phase the total orbital momentum of nuclei / atoms increases?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook