Physics Chapter 1: Principal System of Units

Chapter 1: Principal System of Units

• Physics is an experimental science, a science of measurements.
• Accurate and reproducible measurements are crucial.
• Units are essential for ensuring accuracy and reproducibility.
• Measurement of a quantity is expressed as a number and a unit.

Physical Quantities

• Basic/Fundamental Quantities: Length, Mass, Time, Electric current (ampere), Temperature (Kelvin), Luminous intensity (candela), Amount of substance (mole).
• Derived Quantities: Combinations of basic quantities (e.g., velocity = distance/time, force = mass x acceleration).
• Energy (E) = force x distance

Standards

• Standards are needed to measure any quantity, so standards need to be defined.
• Standards should be durable and have a stable chemical structure.
• Length: The distance between two lines on a platinum-iridium bar (1 meter) or the wavelength of orange-red light from a krypton lamp (1 meter = 1650763.73 λk). Another way to define a meter is the distance light travels in a vacuum in 1/299 792458 of a second.
• Mass: Mass of a platinum-iridium cylinder (1 kilogram).
• Time: The time between successive appearances of the sun ("solar day") or it's 1/86400th of a mean solar day. 1 second is also equal to 1 / 31556925.974 of tropical year or 1/9192631770 oscillations of radiation emitted by cesium atoms.

Systems of Units

• CGS: Centimeter-Gram-Second system
• MKS (SI): Meter-Kilogram-Second system
• fbs (British): Foot-Pound-Second system
• Units must be the same on both sides of an equation.

Multiples and Submultiples (Fractions) of Metric Units

• Prefixes correspond to powers of 10.
• Each prefix has a specific name and abbreviation (e.g., kilo, mega, milli, micro).

Unit Conversion

• Converting units within a system or between different systems.
• Conversion factors are rearranged forms of equalities.

Dimensions

• Dimensions of a physical quantity specify its nature (e.g., length, time, mass, energy).
• Common dimensions include Length [L], Mass [M], and Time [T]
• Different systems of units use different units for the same dimension.

Dimensional Analysis

• Verification/check of physical equations.
• Derivation of relations between physical quantities.
• Determining dimensions of constants.
• Dimensions can be treated as algebraic quantities.
• Quantities are added or subtracted only if their dimensions are the same.

Chapter 2: The Laws of Motion

The Concept of Force

• Force causes changes in motion (acceleration or direction changes).
• A force is a push or pull.
• Forces don't always cause motion (balanced forces).
• The net force on an object is the vector sum of all forces acting on it.
• If the net force = 0, the object is not accelerating (constant velocity or at rest).
• If the net force ≠ 0, the object accelerates.

Balanced and Unbalanced Forces

• Balanced forces: Equal in magnitude, opposite in direction.
• Unbalanced forces: unequal forces, cause acceleration.

Newton's Laws of Motion

• 1st Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion with the same velocity unless acted upon by an unbalanced force.
• 2nd Law (Force = mass x acceleration): The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
• 3rd Law (Action-Reaction): For every action, there is an equal and opposite reaction.

Inertia

• Inertia is an object's resistance to changes in its state of motion (rest or constant velocity).
• Mass is a measure of inertia.
• More mass = more inertia.

Types of Inertia

• Inertia of rest: Resistance to change in its state of rest
• Inertia of motion: Resistance to changes in its state of uniform motion
• Inertia of direction: Resistance to changes in its direction of uniform motion

Mass and Inertia

• Mass: The amount of matter in an object, independent of surroundings or measurement method.
• Units: Kilograms (kg) or grams (gm).
• Inertia: A measure of how an object resists changes in motion. -More mass = more inertia.

Newton's Second Law (Force, Mass, and Acceleration)

• Acceleration is directly proportional to the net force and inversely to the mass.
• Units of force are Newtons (N)

Force of Gravity and Weight

• Gravity is an attractive force between Earth and objects.
• Weight is the magnitude of the force of gravity (w = mg).
• Acceleration due to gravity (g) ≈ 9.8 m/s².

Weight

• Measure of the force of gravity on an object's mass.
• Units are Newtons (N).

Newton's Third Law

• Action-reaction force pairs always act on different objects
• The action force and the reaction force have the same magnitude, but opposite directions .

Forces of Friction

• Friction resists motion between surfaces.
• Friction force is opposite to motion
• Determined by roughness and force pressing surfaces together.

Types of Friction

• Static: Resists start of motion.
• Sliding/Kinetic: Resisting motion when surfaces are sliding against each other.
• Rolling: Resistance opposing rolling motion.
• Fluid: Resistance in liquids or gases.

Coefficients of Friction

• Dimensionless constant
• Depends on the surfaces
• Values vary based on the nature of the surfaces.