Interesting... I performed public demonstrations in chemistry at the Ann Arbor Hands-On Museum for a year. In the exhibit hall, they had a couple of metal plates on long pins. You sprinkled sand on the plates and drew a horsehair bow over them and watched the grains dance into standing wave patterns.

In my shows, I made fireworks from common household salts. I said that the grownups know science books that show the electrons as little balls with minus signs. But really, they are standing waves like the metal plates out in the exhibit hall and their wave patterns are what we see as red, green, etc.

I can perceive the force... Still not convinced I can perceive the mass. Hit me with a hollow metal pipe vs. an apparently identical (but much more "massive") solid metal dowel rod, and I'll be knocked silly... I just won't know how silly until I feel the force.

Your sense of touch exists and is sufficient to validate (perceive) mass for your brain. Like getting hit by a two X four.upside the head.

What you see are photons at specific wavelengths.

I might be wrong, but gravity is one of only 4 forces, all of which have the same basic formulation and require 2 or more bodies. The formulation is that the force is proportional or inversely proportional to the square of the distance between the bodies multiplied by a normalizing constant. As far as I know only gravity and electromagnetism can be directly perceived, but only in a relative way in relation to 2 or more bits of matter.

I think you're at least partly right though - when you accelerate in a car, you do, in fact, perceive the electromagnetic force preventing your body from pushing back through your seat... That's really applying a different kind of acceleration though, not a different force, and it still requires multiple bodies undergoing equal and opposite reactions.

It is tempting to say that because we can perceive the force and know that it increases proportionally to the acceleration that something must exist to explain why bodies with more protons, neutrons, and electrons react more violently than bodies with fewer protons, neutrons, and electrons under the same acceleration... Still, this doesn't mean that we can directly perceive mass.

If two empty trucks are about to collide and two identical, but full trucks are about to collide at the same speed, I know that there will be lots of of violence, noise, and debris, but I wouldn't perceive any particular difference before the collisions.

The equation applies to all forces, not just the case when the acceleration is due to gravity. Can't we understand mass simply by exerting a force other than gravity and seeing that F = ma?

Weight is a relative perception though (i.e. this is heavier than that). I believe that current conventional wisdom is that neither relativistic mass nor weight are intrinsic properties of matter independent of velocity or acceleration (matter is said to have more relativistic mass at higher speeds and more weight at higher acceleration). It takes 2 or more bodies of matter attracting one another or colliding with one another to create the perception of weight/force.

Force = Mass X Acceleration. I can't help but wonder whether Ayn Rand would accept mass as a valid concept given that it cannot be traced back to perceptual reality. Weight can certainly be perceived, but how does one perceive mass? It's a conundrum for me. I thought it might be an interesting talking point.

What does this mean? "For that matter, did Newton's F=MA invent mass, or is MA a singular entity observable only by means of the relative weights (forces) of objects where A is cancelled out by the gravitational acceleration at the location of the scale measuring the weights? "