Matter, force, motion, and friction
The concept of matter.
We know that physics began with the more or less qualitative passive observation of obvious natural phenomena, such as the downward motion of a freely falling body, the tides of the ocean, the lightning, the rainbow, the mysterious behaviour of magnets, etc. Very early there then came to be looked upon as properities of this basics, i .e., the thing called matter. Just what matter is, was never quite clear. Even today we cannot say with confidence what matter is, but we still talk about a great many physical phenomena as properities of matter, and with the greatly increased study of atomic structure we feel that we are some reaching gradually a clearer understanding of the constitution of matter.
