Random Force & Brownian Motion - Sixty Symbols

the symbol today is eater which is a symbol for a random force so this is a greek eater which is a strain symbol with a vector over the top a random force is one that acts this way or that way and as the time changes it goes in one direction then another then another and it seems to go in all directions of the compass one after the other very quickly the random force appears or first appeared to a Roman person who saw dust particles jittering about in the air when the sunlight came into the dusty room and he could see the particles jittering about but it was first noticed scientifically by Robert Brown who was a botanist who saw that if you got pollen molecules and you took the pollen out and sprinkled it on the surface of water and studied it under a microscope you would see the polymer molecules jittering about on the surface of the liquid on the water and he thought that this showed that pollen was alive in something moving all the time chittering it everywhere so he then tested this idea by putting grains of sand on the surface or dust or any other particles he could find and he found that inert particles such as a bit of sand ground-up would also jitter around and this phenomena is known as Brownian motion after Robert Brown who discovered it and it laid hidden away in the literature until it was resurrected in 1905 by Albert Einstein in his year of miracles where he did the most amazing work of his career he gave an explanation of Brownian motion in terms of a random force which is moving this particle backwards and forwards in a dis remotion in fact the jittery motion shows according to Newton's laws the force is the mass times the acceleration it was accelerating every which way and as a result then must experimentally be around and force so I'm going to show you a demonstration of this but I'm not going to use water with grains of pollen on it I'm going to do it using grains of bronze which makes up the liquid so you can actually see the motion of the grains around bashing things and I'll put a grain of pollen on the top which will actually be a polystyrene little thing so what I have here these are the grains of bronze and this is the polystyrene blob and if I put this into moat oscillation it jiggles about if I put the grain on the top it goes in a random motion jittery motion and moves to the side if I do it again put it in the middle I can't get it exactly in the middle so it's not exactly the same and now maybe it'll go another way and it does and each time you do it you might get a completely different path down at the very small level are you focusing in on this Brady a very small level there are little grains coming in if I pick one up I can't and it baths into the side then this will get it that way another one will come and jitter it and ping it that way so it's as though you're playing you're on a billiard table and all these balls are whizzing around in all sorts of directions you put a balloon in the middle and these balls are bashing around in all sorts of directions and sometimes it's kicked one way sometimes it's kicked another way so this is the idea that there are little molecules in here in the water that are acting in this way and some of them are hitting one side of the balloon and other time as heating the other side and that's causing this jittery motion which is why bruh Bert Brown thought that this this thing was alive so you do this lots and lots of times and you'll suddenly get the view that you can work out what's going on using Newton's laws of motion and that's what Einstein did he worked out from this that you could measure the diffusion of this pollen grain on the surface and measure the diffusion constant but there's something else if this is moving through this liquid against all these pollen grains which are moving there's a frictional force as well and if you measured that frictional force of a grain moving in a fluid which is known from Stokes whose formula you could work out this frictional force as well and from the two you could measure the kinetic energy of the particle so what you're getting in effect is the kinetic energy which is the amount of agitation it has and you can relate that to the temperature of this liquid the absolute temperature and that's what Einstein discovered that you could combine Newtonian mechanics with this random force to thermodynamics with gases and liquids having a temperature an absolute temperature this connection he predicted and Peron went away or I think it's para went away and did the experiments and measured all of this and proved it was correct for which Parrington got the Nobel Prize Einstein didn't the randomness comes because these particles come and hit it on each side seemingly at random of course Newton's law says you could work all this out but you can never work it out precisely so you can't really predict how this is going to hit which side it's going to hit and how big a force it's going to be so that's why we treat it as random of course you might believe it's deterministic and my friends might do then but if you do that then I will invoke quantum mechanics and say we can't actually specify everything that precisely so this is the random force and its effect on physic have I finished

Channel: Sixty Symbols

Views: 311,047

Rating: 4.951036 out of 5

Keywords: random, force, brownian, motion

Id: FAdxd2Iv-UA

Length: 5min 35sec (335 seconds)

Published: Wed Feb 17 2010