Originally Answered: Law vrs theory. like evolution differs from gravity?
Scientifically speaking, a theory is GREATER than a law. Theories are the MOST ACCEPTED status that any scientific idea can attain.
Laws only explain specific, observable, repeatable events in similar circumstances. They do not posit a mechanism or explanation for the event. Theories do this by encompassing laws and placing/explaining the them in a context with other laws, evidence, facts, models, hypotheses, and observations.
For example, there is an Ohm's Law, a Fick's law of diffusion, and a Hopkinson's law...but all of them fall UNDER the umbrella of the electromagnetic theory. The laws serve to support the theory.
Also, while Newton did formulate a universal law of gravitation, the larger concept and study of gravity itself is a theory.
Newton's law of gravitation states that "every point mass attracts every other point mass by a force pointing along the line intersecting both points. The force is directly proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses."
But this only tells us how two bodies will react under the influence of gravity. It does not tell us what gravity is, where gravity comes from, what gives gravity the force it has, etc. The theory of gravity contains all those ideas AND the law of universal gravitation within it.
Laws are more like "If A happens, then B will happen."
Theories are more like "B will happen BECAUSE..."
It is an old misconception that there is some mythical and direct chain of events that says hypotheses become theories and theories become laws, but this is simply untrue. No doubt your teachers taught you incorrect or outdated understandings of science. Most basic science textbooks nowdays correct the old myth of any clear, linear science promotion for ideas.
For the record gravity is a theory.
The fact that your body is made up of cells is also a "mere" theory (cell theory). It will NEVER become a "law" that you are made of cells. Never. Yet the whole of modern medicine is built upon the idea and you can easily look at your own cells under a microscope.
The fact that the moon goes around the earth and that the earth goes around the sun are also scientific theories--because these are known to be absolutely, factually true and "theory" the highest form of scientific acceptance (it is the heliocentric theory, not the heliocentric law--and it never will be).
That the axial tilt of the earth causes the seasons is a theory.
Nuclear fission is a theory (one so well proven we built one hell of a bomb on it).
Electro-magneticism is a theory.
Everything being made of atoms is known as atomic theory.
That light and sound travel in predictable, controllable, alterable, measurable waves is wave theory.
Etc. etc. etc.