Before you can break a law, you have to know it. The laws of physics are Newton’s three laws: 1. Inertia, an object at rest tends to stay at rest, 2. "The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body" and 3. For every action there must be an equal and opposite reaction. You can read more about these laws at About.com. Then there is the law of gravity, which states that every object in the universe attracts every other object in the universe. This is only part of the gravity story and you can find out more at About.com. There are the laws of the conservation of energy (the famous e=mc2) and conservation of momentum where the momentum of a closed system is constant. In other words if nothing else is acting on an object in motion, it will remain in motion. This almost sounds like a restating of Newton’s first law, but it refers to motion. In space if you push something away from you, and you are far enough away from any major bodies, it will continue to move away from you forever. Of course, according to Newton’s third law, you will be moving in the opposite direction forever. There are other laws governing thermodynamics and electrostatic and such as well as the speed of light, which states that, in a vacuum, the speed of light is constant and doesn’t change with a viewer perspective.
Now that we know a few of the laws, how can we break them? The answer is, in this world, we can’t, but what if we were in a fictional world? Couldn’t we break them there? It would depend on the world and its governing laws. No matter where you set your fiction, it has to make sense within the realm of that setting. Look at your favorite fiction. If there were no rules, the hero could solve the story problem in the second paragraph after it was stated and the story would be over. Where’s the fun in that? So you have to limit your characters to actions that are believable in the setting where you have placed them. That’s world building.
If your story is set on Earth, starring humans, you won’t have to do much world building. You can just use the world around you. All you have to do is create a culture and you are off and running or writing, rather. Culture, you say. Yes, culture is part of world building. Your characters inhabit a culture, a set of ethical norms for them and the people around them. These norms are the ethical framework that makes up your characters. Someone living in a small town in Ohio would have different norms from someone living in Hollywood. The majority of their norms might be the same, but there would be some tiny differences. Contrast the Hollywood citizen with a member of a Bedouin tribe in Africa. Here the differences would be greater. Fiction has to make some sort of sense to the reader or it will stop reading. If you set your characters on a space ship that encounters the center of the universe where pushing something doesn’t make it move, the object had better be much bigger than the exerting force, or have some other plausible explanation or your reader will close the book and wander away. Plot and Character need a place to be. That’s your setting. That’s your world and you had better build it well if you want your readers to stick around.