Key Concepts in Physics

1. Fundamental Forces

Gravitational Force: Attraction between masses; it governs planetary motion.
Electromagnetic Force: Interaction between charged particles; responsible for electricity and magnetism.
Weak Nuclear Force: Involved in radioactive decay and particle interactions.
Strong Nuclear Force: Holds protons and neutrons together in atomic nuclei.

2. Laws of Motion

Newton's First Law: An object in motion remains in motion unless acted upon by a net external force.
Newton's Second Law: Force equals mass times acceleration (F = ma).
Newton's Third Law: For every action, there is an equal and opposite reaction.

3. Energy

Kinetic Energy: Energy of motion; calculated as KE = 1/2 mv².
Potential Energy: Stored energy based on position; gravitational PE = mgh.
Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

4. Thermodynamics

Zeroth Law: If two systems are in thermal equilibrium with a third, they are in equilibrium with each other.
First Law: Energy conservation; change in internal energy = heat added - work done.
Second Law: Entropy of an isolated system always increases; heat flows from hot to cold.
Third Law: As temperature approaches absolute zero, entropy approaches a constant minimum.

5. Waves and Oscillations

Wave Properties: Wavelength, frequency, amplitude, speed.
Types of Waves:
- Transverse: Particles move perpendicular to wave direction (e.g., light waves).
- Longitudinal: Particles move parallel to wave direction (e.g., sound waves).
Superposition Principle: When two waves meet, the resulting wave is the sum of the individual waves.

6. Electricity and Magnetism

Ohm's Law: Voltage = Current x Resistance (V = IR).
Circuit Components:
- Resistors: Oppose current flow.
- Capacitors: Store electric charge.
- Inductors: Store energy in a magnetic field.
Magnetic Fields: Produced by moving charges; described by the right-hand rule.

7. Modern Physics

Theory of Relativity:
- Special Relativity: Time and space are relative; speed of light is constant.
- General Relativity: Gravity is the curvature of spacetime caused by mass.
Quantum Mechanics: Describes behavior of particles at atomic and subatomic scales; wave-particle duality and uncertainty principle.

8. Astrophysics

Big Bang Theory: Origin of the universe from a singular point; explains cosmic background radiation and expansion of the universe.
Black Holes: Regions of spacetime with gravitation so strong that nothing can escape from them.
Dark Matter and Dark Energy: Components that make up the universe; dark matter interacts via gravity, while dark energy is responsible for the accelerated expansion of the universe.

Fundamental Forces

Gravitational Force: Attracts objects with mass. Everything with mass pulls on everything else with mass. This is how planets orbit stars and the Moon orbits Earth.
Electromagnetic Force: Arises from charged particles like electrons and protons; it's why magnets stick to metal and electric currents flow.
Weak Nuclear Force: Responsible for radioactive decay; involved in the decay of protons and neutrons to other particles.
Strong Nuclear Force: Binds protons and neutrons together within the nucleus of an atom. The force that holds the nucleus together despite the protons repelling each other due to their positive charges.

Laws of Motion

Newton's First Law (Inertia): An object at rest will remain at rest, and an object in motion will stay in motion at a constant velocity unless acted upon by a net external force.
Newton's Second Law: The force acting on an object is equal to its mass multiplied by its acceleration. This is expressed as F = ma.
Newton's Third Law: Every action has an equal and opposite reaction. For example, when you push a wall, the wall pushes back on you with the same force.

Energy

Kinetic Energy: Energy an object possesses due to its motion. The faster the object moves, the more kinetic energy it has. It's calculated with the equation KE = 1/2 *mv², where m is mass and v is velocity.
Potential Energy: Energy stored by an object due to its position. A book on a shelf has gravitational potential energy because of its position above the ground.
Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed from one form to another. For example, a battery converts chemical energy into electrical energy.

Thermodynamics

Zeroth Law of Thermodynamics: Two systems in thermal equilibrium with a third system are also in thermal equilibrium with each other. This basically means two systems at the same temperature will exchange no heat when brought into contact.
First Law of Thermodynamics: Energy is conserved. The total energy of an isolated system remains constant.
Second Law of Thermodynamics: The entropy of an isolated system always increases over time. This means that disorder tends to increase in a system.
Third Law of Thermodynamics: The entropy of a system approaches a constant minimum as the temperature approaches absolute zero. This is essentially saying that the entropy of a perfect crystalline solid at absolute zero is zero.

Waves and Oscillations

Wave Properties:
- Wavelength: Distance between two successive crests or troughs of a wave.
- Frequency: Number of waves passing a point per second.
- Amplitude: Maximum displacement of a point from its equilibrium position.
- Speed: How fast the wave travels through a medium.
Types of Waves:
- Transverse Waves: Particles oscillate perpendicular to the direction the wave travels. Think of a wave traveling on a string.
- Longitudinal Waves: Particles oscillate parallel to the direction the wave travels. Sound waves are a good example of longitudinal waves.
Superposition Principle: When two waves meet, the resulting wave is the sum of the individual waves. This means that waves can interfere with each other, either constructively or destructively.

Electricity and Magnetism

Ohm's Law: Relates voltage, current, and resistance in a circuit. The voltage across a conductor is directly proportional to the current, provided the temperature remains constant. V = IR, where V is voltage, I is current, and R is resistance.
Circuit Components:
- Resistors: Oppose the flow of current. The higher the resistance, the more difficult it is for current to flow.
- Capacitors: Store electric charge. Think of a capacitor as a tiny battery; when a charging current flows into the capacitor, it stores an electrical charge.
- Inductors: Store energy in a magnetic field. When an electric current passes through an inductor, it creates a magnetic field that stores energy.
Magnetic Fields: Produced by moving electric charges. The direction of the magnetic field can be determined using the right-hand rule.

Modern Physics

Theory of Relativity:
- Special Relativity: Deals with the relationship between space and time. Key concepts include:
  - Time is relative, meaning it flows at different rates depending on the observer's speed.
  - The speed of light in a vacuum is constant for all observers, regardless of the motion of the light source.
- General Relativity: Explains gravity as a consequence of the warping of spacetime caused by mass and energy. Basically, massive objects warp space and time around them, causing objects to move towards them.
Quantum Mechanics: Describes the behavior of matter at the atomic and subatomic levels. Key concepts include:
- Wave-particle duality: Particles can exhibit wave-like properties and vice versa (like photons behaving as both particles and waves).
- Uncertainty Principle: It's impossible to know both the position and momentum of a particle with perfect accuracy.

Astrophysics

Big Bang Theory: The prevailing cosmological model for the origin of the universe. The universe began in a very hot and dense state and has been expanding ever since. Evidence for this theory includes the cosmic microwave background radiation and the red-shift of distant galaxies.
Black Holes: Regions of spacetime where gravity is so strong that nothing, not even light, can escape. They are formed by the collapse of massive stars.
Dark Matter and Dark Energy: Components of the universe that are thought to be responsible for the universe's expansion and structure. We can't directly see or interact with dark matter, but we know it exists based on its gravitational influence on visible matter. Dark energy, on the other hand, appears to be accelerating the expansion of the universe.