Essential Physics Laws, Units, and Core Concepts

Fundamental Laws and Conservation Principles

• Newton’s First Law: An object stays in uniform motion unless a net force acts (if net force = 0, motion remains unchanged).
• Newton’s Second Law: Acceleration is proportional to net force and inversely proportional to mass.
• Newton’s Third Law: Forces come in equal and opposite pairs (action and reaction).
• Conservation of Energy: Total mechanical energy remains constant if no non-conservative forces act.
• Conservation of Momentum: Total momentum stays constant in isolated systems.
• Archimedes’ Principle: Buoyant force equals the weight of displaced fluid.
• Bernoulli’s Principle: Faster fluid → lower pressure; slower fluid → higher pressure.
• Pascal’s Principle: Pressure applied to a fluid transmits equally in all directions.
• Faraday’s Law: Changing magnetic flux induces an electromotive force.

Basic Definitions and Symbols

• Electric Field: Region where a charge experiences force.
• Potential Difference (Voltage): Energy per unit charge.
• Current: Rate of charge flow.
• Resistance: Opposition to current.
• Magnetic Field: Region where magnetic forces act.
• Induced Electromotive Force: Voltage created by changing magnetic flux.
• Magnetic Flux: Amount of magnetic field passing through an area.
• Node (waves): Point of zero displacement.
• Antinode: Point of maximum displacement.

Common Symbols and Units

• m (mass): kilogram (kg)
• W (weight): newton (N); depends on gravity
• F (force): newton (N)
• d (distance/displacement): meter (m)
• t (time): second (s)
• v (velocity): meters per second (m/s)
• a (acceleration): meters per second squared (m/s²)
• ρ (density): kilograms per cubic meter (kg/m³); water = 1000 kg/m³
• P (pressure): pascal (Pa) = newton per square meter (N/m²)
• V (volume): cubic meter (m³); 1 cm³ = 1 mL
• Q (charge): coulomb (C)
• I (current): ampere (A)
• V (voltage): volt (V)
• R (resistance): ohm (Ω)
• C (capacitance): farad (F)
• B (magnetic field): tesla (T)
• Φ (magnetic flux): weber (Wb)
• f (frequency): hertz (Hz)
• T (period): second (s)
• λ (wavelength): meter (m)

Mechanics: Motion, Forces and Collisions

• Inertia: Resistance to changing motion.
• Equilibrium: Net force and net torque are zero.
• Impulse: Effect of a force acting over time; impulse changes momentum.
• Elastic Collision: Kinetic energy and momentum are conserved.
• Inelastic Collision: Momentum conserved; kinetic energy is lost (may convert to heat or deformation).
• Perfectly Inelastic Collision: Objects stick together after impact.
• Forces (summary): An object stays in motion unless a net force acts; acceleration increases with net force and decreases with mass; forces come in equal and opposite pairs but act on different bodies; constant velocity means net force = 0; equilibrium means net force = 0 and net torque = 0.
• Energy (summary): Energy is conserved when no non-conservative forces act; an object speeding up gains kinetic energy, slowing down loses kinetic energy.
• Momentum (summary): Momentum is conserved in isolated systems; elastic collisions conserve kinetic energy, inelastic collisions do not; sticking together is perfectly inelastic.

Fluids: Pressure, Buoyancy and Hydrostatics

• Fluids (summary): Deeper means higher pressure; larger area decreases pressure for the same force; buoyant force depends only on displaced fluid; density less than fluid means an object floats; density greater than fluid means it sinks; partially submerged objects displace only the submerged volume; underwater objects appear closer due to refraction.
• Buoyancy: Upward force due to displaced fluid.
• Principle of Flotation: An object displaces a weight of fluid equal to its own weight when floating.
• High Pressure: Acts in all directions.
• Buoyant Force: Independent of object weight; depends on displaced fluid volume and fluid density.

Gravity and Orbits

• Gravity: Heavier objects do not fall faster in vacuum; weight changes with gravity but mass does not.
• Circular Motion: Constant speed still implies acceleration toward the center (centripetal acceleration).
• Satellites in Orbit: Satellites orbit by continuously falling while moving forward (free-fall with tangential velocity).
• Escape Speed: Speed that must be reached to leave some gravitational influence.
• Universal Gravitation: Every mass attracts every other mass by the same inverse-square equation.

Simple Harmonic Motion and Waves

• Simple Harmonic Motion: Restoring force proportional to displacement; maximum speed at equilibrium; maximum acceleration at endpoints.
• Waves (summary): Frequency increases → wavelength decreases (wave speed constant in a given medium). Nodes are zero displacement; antinodes are maximum displacement.
• Sound: Travels faster in water than in air.
• Doppler Effect: Change in frequency received compared to frequency emitted.
• Longitudinal Wave: Particle vibration is parallel to wave propagation.
• Timbre: Characteristic sound of an instrument.
• Sonic Boom: Loud sound resulting from a shock wave when an object exceeds the speed of sound.
• Wavelength: Distance between identical parts of a wave.

Electricity, Circuits and Capacitors

• Electricity (summary): Electric field shows the direction a positive charge would move; voltage is energy per charge; current flows from high to low potential; current is the same in series circuits; voltage is the same across parallel branches.
• Resistance: Longer or thinner wires have higher resistance; parallel resistors reduce total resistance.
• Capacitor: Stores electric energy; plates closer together increase capacitance.
• Ampere: Unit of current; direct current is a constant current that flows in one direction.
• Electric Potential: Electric potential energy per unit charge; electric potential energy is the energy of a charge due to its position.
• Generator: Creates current by rotating a coil in a magnetic field.

Magnetism and Electromagnetic Effects

• Magnetic Force: Magnetic force is perpendicular to both velocity and magnetic field (for charged particles); no magnetic force if velocity is parallel to the magnetic field.
• Right-Hand Rule: Applies for positive charges; reverse for negative charges.
• Electromagnet: A magnet formed by a current.
• Magnetic Domain: Regions of aligned magnetic atoms.
• Changing Magnetic Flux: Induces an electromotive force; no change means no induced emf; faster change means larger induced emf.
• Magnetic Field Lines: Show direction and strength of magnetic influence and do not cross.

Optics and Light

• Reflection: Angle of incidence equals angle of reflection.
• Refraction: Entering a denser medium bends light toward the normal; exiting a denser medium bends light away from the normal.
• Convex Lens: Converges light.
• Concave Lens: Diverges light.
• Apparent Depth: Water makes objects appear shallower; an object in water appears closer because light bends when leaving water.
• Polarization: Direction of the electric field oscillations in light.
• Complementary Colors: Add together to produce white light.
• Electromagnetic Wave: Oscillating electric and magnetic fields emitted by vibrating charges.
• Transparent: Materials that allow light to pass through.

Thermal Processes and Material Properties

• Conduction: Transfer of thermal energy through a material.
• Evaporation: Liquid to gas at the surface of a liquid.
• Sublimation: Solid to gas without passing through the liquid phase.
• Specific Heat: Heat required to raise a unit mass by 1 °C.
• Absolute Zero: Theoretical temperature at which no more thermal energy can be removed.
• Power: Rate of doing work.

Additional Terms and Facts

• Fact: Observations with which competent observers agree.
• Normal Force: Prevents objects from phasing into each other; acts perpendicular to contact surfaces.
• Weight: Force of gravity acting on a mass; weight is the force of gravity against a surface.
• Force Pair: Action-reaction force pair according to Newton’s third law.
• Interaction: Mutual action between forces or bodies.
• Terminal Speed: When acceleration stops for a falling object (terminal velocity due to drag equals weight).
• Inelastic Collision: Can produce heat, lasting deformation, or objects sticking together.
• Magn Force: Force between magnetic poles (magnetic force).
• Magn Field: Region of magnetic influence around a pole (magnetic field).
• Magn Domain: Regions of aligned magnetic atoms.
• Electric Cur: Flow of electric charge (electric current).
• Elect Pot: Electric potential—energy per unit charge.
• Elect Pot Energy: Energy of a charge due to its position (electric potential energy).
• Object in Water Appears Closer: Light bends when leaving water, making objects appear shallower.
• Floating vs Sinking: Depends only on densities.
• Satellite in Orbit: Continuous free fall with forward motion.
• Weight vs Mass: Mass is constant; weight depends on local gravity.
• No Air Resistance: In vacuum, all objects fall equally regardless of mass.
• Zero Velocity does not imply zero acceleration (e.g., at turning points in motion).
• Circular Motion with constant speed still has centripetal acceleration directed toward the center.