Air being of lesser density than water, man penetrates air with less effort than he penetrates water. Man cannot penetrate steel because steel is of a greater density than man, and its crevices are not large enough to permit the body of man to pass through. Heat, which is of lesser density than steel, penetrates it in the same manner that water penetrates a metal sieve. The difference in density of heat and water is so great that heat is able to pass through the minute crevices of solid steel whereas water is unable to do so. Heat will also pass through the crevices of water, mix with it and form a combination known as vapor.
Vapor is of greater density than heat and of lesser density than water.
From this one can understand why Penetrability is the basic law of movement, for without penetration nothing would move at all. In Space without size, shape, inside or outside, there is no foundation whatsoever for anything to rest upon. So everything must keep moving forever. There is no up or down in Space, no east or west, no latitude or longitude. Mass in Space is continually falling toward volume and volume in Space is continually drawing mass toward it.