You might be thinking about one of these:
* Newton's First Law of Motion (Law of Inertia): This law states that an object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
* Newton's Law of Universal Gravitation: This law describes the force of attraction between any two objects with mass.
* The First Law of Thermodynamics: This law states that energy cannot be created or destroyed, only transferred or transformed.
* Kirchhoff's Current Law: This law states that the total current flowing into a junction is equal to the total current flowing out of the junction.
To help me answer your question, please tell me which area of physics you're interested in, and I can give you a more specific answer.
