Is there a force related to temperature?

Question

From my understanding, when an object is heated, there is an increase in the average kinetic energy of the molecules of the object. So if the temperature increases the average kinetic energy increases. Consider a molecule in this object. Now kinetic energy of this molecule is proportional to the square of magnitude of velocity. To increase the kinetic energy of this molecule one should have to increase the magnitude of velocity, which would imply the existence of such a force.

If there is no such force, I would very much appreciate an explanation to how exactly is this kinetic energy changing as in what is happening to change the kinetic energy, because if there is no force acting, I find it tough to imagine how the kinetic energy could change.

Answer 1

You appear to be confusing the kinetic energy of an object as a whole, a change in which requires net work (and thus a net force) and is not related to temperature, with the random kinetic energy of the the molecules of an object, which is related to temperature. That molecular kinetic energy, and thus the temperature of an object, can change due to heat without involving any forces doing work.

An example is a ball. To change its velocity and thus its kinetic energy due to its motion as a whole, a net force must be applied. But, ignoring air friction, that change in kinetic energy wouldn't affect its temperature (change its random molecular kinetic energy). Placing the ball in contact with a hot object would.

I seem to have not explained properly, a fault on my part. I meant in an atomic level, as in how are the atoms exactly increasing their velocity, is there a force.

They can increase their velocity in various ways. One is due to collisions with higher kinetic energy molecules when placed in contact with a higher temperature object whose molecules have higher kinetic energy. Of course those collisions involve intermolecular forces that transfer kinetic energy.

Another thing, I do not also seem to understand why does increasing the kinetic energy of the ball over all not increase the kinetic energy of the constituent atoms. I would think that due to relative velocity, now the atoms would have an additional component along the direction of movement,

It does increase the kinetic energy of the constituent atoms of the ball, but only in a reference frame external to the ball. It does not change the velocity of the atoms of the ball with respect to the center of mass of the ball, which is what determines the temperature of the ball,

Imagine you are located at the center of mass of the ball measuring the velocities of the particles of the ball relative to you. Your measurements would be no different if you and the center of mass of the ball were at rest or moving at constant speed in a straight line with respect to an external (to the ball) inertial frame of reference. Moreover, you would not know if you were at rest or moving.

Hope this helps.

Answer 2

The nature of the force (that tends to increase molecular speeds upon heating) depends on the specific heating mechanism.

If one object heats another, the force is applied through interactions with faster-moving molecules in the hotter object, which tend to transfer momentum. Of course, this raises the question of what tended to speed up those molecules.

So let's look at some examples.

If the heating mechanism is Joule heating, for instance, the force arises from acceleration of a charge carrier in an electric field.

If the heating mechanism is friction, the force arises from an external mechanical load and the release of strain energy.

If the heating mechanism is compression, the force arises from an inward-moving container wall, which gives colliding molecules a momentum kick inward.

In all cases, the accelerated molecules soon interact with their neighbors, ultimately "thermalizing" the entire object with a broadened distribution of molecular speeds—i.e., a higher temperature.

Answer 3

There are various ways that the kinetic velocity of molecules can be increased to increase the temperature of the substance.

If we start with a solid object modelled as a crystal lattice we can imagine the atoms being connected to each other with chemical bonds that can be loosely modelled as springs. When radiation from a heat source falls on the crystal the photons literally have momentum and impart this momentum energy to the atoms of the crystal. The momentum of a photon is proportional to its frequency. The atom start moving but due to the spring like nature of the chemical bonds, the atom starts oscillating back and forth in a form of vibration. This oscillating of the surface atoms of the crystal is transfer to the internal atoms through the chemical bonds until the whole solid is vibrating in random directions and this increased vibration or the average kinetic energy of the oscillations is a literal interpretation of the temperature of the solid.

If the solid is not in a vacuum, then this increased vibration of the surface of the solid imparts additional momentum or an accelerating force on the molecules of the gas colliding with the surface of the solid. These accelerated gas molecules fly away from the surface of the solid until they collide with other gas molecules further away from the solid imparting momentum and providing the accelerating force acting on these molecules further away from the solid surface. These continued collisions at random angles in the gas, disperse the energy throughout the gas and increases the average kinetic energies of the molecules, therefore raising the temperature of the gas.

An important concept to grasp is that temperature is the sum of the kinetic energies of the particles making up the substance as measured in the reference frame where the total momentum of the particles is zero.

Answer 4

Every instance of heat conduction occurs with a force, coulomb repulsion that makes each atom jostle against its neighbors.

Every thermal effect has some force associated with it, such as the expansion of gas that makes our internal combustion engines work.

Force, too, is apparent in the electrical force, voltage potentials that make thermocouples work (the voltages being a good indication of temperature differences).

Temperature is a statistic over a system of many particles interacting, and those interactions are all associated with forces.