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First principles in physics refer to the fundamental principles or basic laws that are considered foundational and are not derived from other principles. These principles provide the basis for understanding and formulating more complex theories in physics. Here are some key first principles in physics:

1. Newton’s Laws of Motion:
• Newton’s First Law: 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 external force.
• Newton’s Second Law: The force acting on an object is equal to the mass of that object times its acceleration (F = ma).
• Newton’s Third Law: For every action, there is an equal and opposite reaction.
2. Law of Universal Gravitation:
• Every mass attracts every other mass in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
3. Conservation of Energy:
• The total energy of an isolated system remains constant over time. Energy can neither be created nor destroyed, only transferred or converted from one form to another.
4. Conservation of Momentum:
• The total linear momentum of an isolated system remains constant if no external forces act on it.
5. Maxwell’s Equations:
• These are a set of four fundamental equations that describe the behavior of electric and magnetic fields. They form the basis of classical electrodynamics.
6. Principle of Relativity:
• The laws of physics are the same in all inertial frames of reference. This principle is fundamental to both Galilean relativity and Einstein’s theory of special relativity.
7. Quantum Mechanics Principles:
• Wave-Particle Duality: Particles such as electrons exhibit both wave and particle properties.
• Uncertainty Principle: It is impossible to simultaneously know both the exact position and momentum of a particle.
8. Second Law of Thermodynamics:
• The total entropy (measure of disorder or randomness) of an isolated system tends to increase over time.
9. Principle of Least Action:
• The path taken by a system between two points in configuration space is such that the action integral is minimized. This is a fundamental concept in classical mechanics.
10. Planck’s Law of Black Body Radiation:
• Energy emitted or absorbed by a black body is quantized and is proportional to the frequency of the radiation.

These principles form the bedrock of classical and modern physics, providing the foundation for understanding the behavior of matter and energy in the universe.