Rissam

I have been taught this definition of physics "Physics is the branch of science which deals with the study of matter and energy and their mutual releationhip" As in the case of motion, matter is in motion due to its internal energy. Motion also releates matter and energy. Nuclear reactions also involve matter and energy. So any thing that deals with matter and energy is physics. We can say that everything is physics. Chemical reactions in Chemistry and working of organs in biology involves matter and energy so they are somehow physics. Apart from this "Physics is the mother of all sciences".

By the way air around us is invisible. So lets assume we are made up of any one gas only (e.g oxygen , hydrogen etc) and the density of our body(made of air) is very high but it is still gas( not liquid or solid) and our body is voluntary in action. It is hard as a solid object that it does not get blown away like air. So can we be invisible?