Physics Essentials

Physics is the fundamental natural science that studies matter, its fundamental constituents, motion and behavior through space and time, and related entities like energy and force.

The base SI units are the metre (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current, kelvin (K) for temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity.

Scalar quantities have only magnitude, such as mass or speed, while vector quantities have both magnitude and direction, such as velocity or force. Vectors are represented by arrows indicating direction and length for magnitude.

Distance is the total path length traveled, a scalar, while displacement is the straight-line vector from initial to final position. Displacement can be zero even if distance is not, as in a closed loop.

Speed is the scalar rate of change of distance with time, while velocity is the vector rate of change of displacement with time. Average speed is total distance over time; average velocity is displacement over time.

Acceleration is the rate of change of velocity with time, a vector quantity. It can be positive, negative (deceleration), or change direction, calculated as a = Δv / Δt.

The equations are: v = u + at, s = ut + (1/2)at², and v² = u² + 2as, where u is initial velocity, v final velocity, a acceleration, s displacement, t time.

Newton's First Law states that an object at rest stays at rest and an object in motion stays in motion with constant velocity unless acted upon by a net external force. This describes inertia.

Newton's Second Law states that the net force on an object equals its mass times acceleration: F_net = ma. Acceleration is directly proportional to force and inversely to mass.

Newton's Third Law states that for every action, there is an equal and opposite reaction. Forces come in pairs acting on different objects.

Mass is the amount of matter in an object, measured in kg, invariant. Weight is the gravitational force on mass, W = mg, varying with location.

Friction is the force opposing relative motion between surfaces in contact. Static friction prevents motion; kinetic friction acts during sliding, both proportional to normal force.