Physics is the scientific study of matter and energy and how they interact with each other.

This energy can take the form of motion, light, electricity, radiation, gravity . . . just about anything, honestly. Physics deals with matter on scales ranging from sub-atomic particles (i.e. the particles that make up the atom and the particles that make up those particles) to stars and even entire galaxies.

In a broader sense, physics can be seen as the most fundamental of the natural sciences. Chemistry, for example, can be viewed as a complex application of physics, as it focuses on the interaction of energy and matter in chemical systems. We also know that biology is, at its heart, an application of chemical properties in living things, which means that it is also, ultimately, ruled by the physical laws.

Science without religion is lame, religion without science is blind.
-Albert Einstein

A scientist in his laboratory is not a mere technician: he is also a child confronting natural phenomena that impress him as though they were fairy tales.
 -Marie Curie

Somewhere, something incredible is waiting to be known.
 -Carl Sagan

My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all.
 -Stephen Hawking

Physics constitutes a logical system of thought which is in a state of evolution, whose basis (principles) cannot be distilled, as it were, from experience by an inductive method, but can only be arrived at by free invention. The justification (truth content) of the system rests in the verification of the derived propositions (logical truths) by sense experiences (empirical truths). Evolution is proceeding in the direction of increasing simplicity of the logical basis (principles). We must always be ready to change these notions - that is to say, the axiomatic basis of physics - in order to do justice to perceived facts in the most perfect way logically.
 -Albert Einstein