Friction...

Ever wondered what friction actually is? If so then don’t worry you’re not alone, I've often questioned what the actual mechanics behind the force are, and I’ve come up with an answer.


As we’re all told in primary school, friction is the force that acts on two objects when they contact one another. The question is just what is this force?


Well every object is made up of molecules, which are made up of atoms. When two objects touch one another the molecules in the objects form relatively weak electrostatic intermolecular bonds (weak compared to intramollecular bonds such as ionic or covalent bonds) with one another. It is these attractions that need to be broken when two objects move apart or slide over each other.


Now although the attractions are weak they still exist and in great numbers, so some energy needs to be used to break the attractions. This is where the term friction really comes into being. To break the bonds, say between your two hands when they’re pressed palms together, you need to apply kinetic (movement) energy to break all the tiny attractions between the surface molecules of one hand and the molecules of the other, to do this you may apply a rubbing motion.


When you break bonds the bonds need to absorb energy to do so, this is known as being endothermic (A process that absorbs energy from its surroundings). So when you rub your hands together the action of you rubbing your hands provides the energy to break the bonds, and this kinetic energy is transferred to the bonding molecules on the surface of your hands, breaking their bonds with one another and in the process transferring some of the kinetic energy to them, making them more energetic.


This energy means that the molecules that make up the surface of your hands bump into each other more and the kinetic energy becomes thermal (heat) energy, and this is why your hands heat up when you rub them together. The same thermal increase happens when ever friction arises between two moving surfaces.


So in summary, friction is the force that needs to be applied to overcome the electrostatic intermolecular bonds that form between two objects in contact, i think.