Physics Notes: Key Concepts
1. Newton's Laws of Motion
First Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion at a
constant velocity unless acted upon by a net external force.
Second Law (F = ma): Force equals mass times acceleration. This explains how the velocity of an
object changes when it is subjected to an external force.
Third Law (Action-Reaction): For every action, there is an equal and opposite reaction.
2. Energy
Kinetic Energy (KE): The energy of motion, given by the formula KE=12mv2KE = \frac{1}
{2}mv^2KE=21mv2, where mmm is mass and vvv is velocity.
Potential Energy (PE): The energy stored due to an object’s position, especially in gravitational
fields. PE=mghPE = mghPE=mgh, where mmm is mass, ggg is the acceleration due to gravity, and
hhh is height.
3. Laws of Thermodynamics
First Law: Energy cannot be created or destroyed, only transformed (conservation of energy).
Second Law: The total entropy (disorder) of a closed system will always increase over time.
Third Law: As temperature approaches absolute zero, the entropy of a system approaches a
constant minimum.
4. Waves
Frequency (f): Number of waves passing a point per second. Measured in Hertz (Hz).
Wavelength (λ): Distance between successive crests of a wave.
Speed of a wave: v=f×λv = f \times λv=f×λ.
5. Electromagnetism
Electric Field (E): A field produced by electric charges, exerting force on other charges. The
strength of an electric field is E=FqE = \frac{F}{q}E=qF, where FFF is the force, and qqq is the
charge.
Magnetic Field (B): A field produced by moving electric charges or by certain materials like iron.
Electromagnetic Waves: Waves that propagate through space carrying electromagnetic
radiation, including light. These waves have both electric and magnetic field components.
6. Relativity
Special Relativity (Einstein): Time and space are relative and depend on the observer's speed.
Famous equation E=mc2E = mc^2E=mc2, which describes how mass can be converted into
energy.
General Relativity: Describes how gravity is not a force but a curvature of space-time caused by
mass.
7. Quantum Mechanics
Uncertainty Principle (Heisenberg): It is impossible to know both the exact position and the
exact momentum of a particle at the same time.
Wave-Particle Duality: Particles such as electrons exhibit both wave-like and particle-like
behavior.
Quantum Superposition: A system can exist in multiple states simultaneously until measured.
