Smell

Smell is the sensation of fast moving particles.

This is why hot air is more conductive to smell, and cold air isn't so much.

Plants, for example have smell as a form of communication to attract pollinators.

Any stream of fast moving particles can be though of as increasing the internal energy of the system of those particles. High internal energy will lead to more sensation of smell.

But not all particles in rapid motion are understood by the human senses, just like how we cannot pickup all frequencies of sounds.

Experiment to quantify smell

Assumption: Smell is the measure of "internal energy" of known particles, rather than the "amount" of particles.

Experiments to do:

• Try inhaling the same number of moles of a particle, but at different temperatures, and see if there is a difference in smell

• Try inhaling a lower number of moles of a particle and a higher number of moles of the same particle, but with the lower number of particles having a higher temperature

• Keep in mind that the particles have to be properly inhaled, and no significant particles should be lost in the experiment.

How to setup an experiment:

• Find a type of particle
  • A candidate in my opinion would be water mixed with Tulsi leaves, or maybe a quantifiable amount of a herbal therapeutic inhalant.
• Heat the vessel so that vapours are generated
• We know that by ideal gas laws, PV=nRT
  • Since PV is a measure of the "internal energy" of the particle system (I was trying to say the rest of it, but while writing, I just noticed that PV is exactly what I want to measure), n \(\propto\) PV/T. That is, for lower higher temperatures, the Pressure and Velocity product can vary. So our apparatus should take that into consider by having a constant pressure chamber that expands with temperature, or a constant volume chamber that regulates the maximum pressure. I think the latter is more experimentally feasible (the former would need something like a balloon?)
    • This makes me curious about how a balloon works. If we assume constant temperature, we are blowing more number of particles into the same space. So, the internal energy of the balloon increases, which is compensated by an adjustment of pressure and volume due to elastic expansion. The pressure forces the balloon to expand,
    • I have also heard from Richard Feynman that rubber bands work on the principle of long chains of molecules trying to get tangled up due to the bombardment of other rapidly moving particles rather than be ordered. So, when heating up a rubber band, it has a tendency to crumble up further, because you increase the kinetic energy of these particles, leading to shrinking of the rubber band. I believe this applies to balloons too. So heating up a balloon to increase it's volume would.. increase the pressure of the air and also shrink the size of the balloon? These would counteract each other, and I'm curious to how it would play out.
      • I'm expecting the balloon to burst, because while the elastic force increases forcing a decrease in volume, that alone would increase the air pressure, and since heating increases internal energy, it would just fight against the compression with added pressure. The question is, will the balloon burst faster, or will it just be able to contain more pressure (to an extend, assuming the elastic compression matches the internal energy). In other words, will stretching a heated (and hence shrunk) rubber band make it snap at a smaller level of expansion compared to a cold one?
  • Also, PV=nRT is the ideal gas law, real gases have other aspects to consider, such as Van der Waals forces.
  • So we'll need

Notes

• Generally, smell is viewed as the reaction of the receptors in the nose to the presence of certain particles. I find that misleading, as even vision is the reaction of the photo-cells in the eyes to electromagnetic waves and the hair cells of the cochlea in the ears to vibrations in the air; yet we don't refer to them as just reactions to the presence of some form of particles or energy. If that was the case, we would refer to vision as "reactions" to the eyes to photons, and sound as the "reactions" of the ears to air phonons, or (oscillating air molecule bundles - just as much of an abstraction as photons are for the electromagnetic field ripples) instead of the "perception" of those particles.