This is a key exercise for your brain to develop and maintain the mind's eye and non verbal, symbolic and spatially oriented thought. Like internal monologue, it's something that many people seem to lack Imagine a key, spin the key, imagine a lock, insert the key into the lock and turn the key. See the lock unlock, remove the key, etc A great way to start practicing this is to get a good night's sleep, like 8 hours or more. In the last hour of rest your visually imaginative capabilities are at their peak. As you slowly begin to awake, think of specfic things and mind will show them to you. Then manipulate those things like in the example above. Eventually you can do this even during waking hours and your abstract cognitive abilities will increase. Mastering this technique is how you can start lucid dreams

But can you feel the densities of the materials of those parts?

That's easy. When you start breaking them apart down to their genetic and molecular structure, you'll be on my level.

I took an organic chemistry class, and killed it because I was able to do this.

That's pretty straightforward. They must be stupid.

This is a good mental exercise, I am trying it right now...very interesting.