Fundamentals Of Physics 5c)
Falsification of Kinetic Theory
Convection
Kinetic Theory gives no clear explanation of heat transference between different materials, it fails to explain, for example, how this in a gas or a liquid causes a localised convective movement.
Textbooks brush over this very important heat transfer process by vague phraseology such as ‘In free convection the heating process produces a temperature and density gradient in the fluid and fluid motion is induced by the action of gravity’ and ‘temperature gradients induce convection in fluids, a phenomena that involves the movement of gases or liquids’.
The example above is a hot object placed in contact with a ‘kinetic’ gas that is at a lower temperature. What occurs in practice is that where the gas meets the object convection currents are clearly observed rising close to the surface of the object.
Kinetic Theory states that ‘Molecules that move more rapidly because they are in a region of higher temperature collide with molecules in a neighbouring region, giving the adjacent molecules more kinetic energy and consequently more thermal energy’, and that ‘heat applied to a gas results in an increase in the velocity of the molecules and a corresponding increase in collisions’ and that this increase in collisions results in a greater average molecular separation.
Clearly this would mean that where this occurs there would be fewer molecules per unit space and the total mass and therefore the density of this unit volume would be reduced by comparison with adjacent cooler unit volumes of gas.
However if a gas consists of molecules moving independently of each other in a vacuum and as the mass of these molecules remains the same and further there is ‘no attraction between molecules’, then gravity can only act on individual molecules and not the gas as a whole because the theory states that the gas as a whole is 99.9% a vacuum and this component cannot be influenced by gravity. In any case the theory also suggests that as far as individual atoms are concerned “gravity can be ignored”.
If we put this into a different perspective, this is like saying that if a number of ball bearings are suspended on wires (as in the diagram below) with a separation between them of say 20mm, and beside this suspend a similar number at separations of 40mm, then the second group would collectively have a lesser gravitational attraction to the centre of the Earth than the first group. This of course is absurd.
It follows therefore that an individual molecule in a larger volume of space has the same gravitational attraction as another molecule of the same mass in a smaller volume of space.
But Kinetic Theory is suggesting that a single molecule in a larger area of ‘space’ moving at greater velocity has a lower gravitational attraction to the earth than a slower one of the same mass in a smaller area of ‘space’. However it is the ‘space’ that has expanded and the ‘space’ cannot be affected by gravity as it is devoid of matter.
Or to put it in another way if the mass of the molecule remains the same, the gravitational effect in a vacuum would be unchanged, and it is quite clear that this kinetic process, in itself, would not result in these observed convection currents.
The only way this could occur in such circumstances is for there to be some instantaneously acting force of attraction acting between these atoms, but as the theory states that there is ‘no attraction between molecules’ the natural phenomenon of convection cannot be described by the kinetic atomic theory of gases.