Physics Fundamentals
This section covers the basic principles of physics, focusing on the essential concepts of units, dimensions, and the classification of physical quantities.
Physical Quantities
In physics, we measure and quantify the world around us using physical quantities. These are broadly divided into two categories:
- Fundamental Quantities: These are the seven basic building blocks of all physical quantities. They are independent and defined by a standard. They include Length (L), Mass (M), Time (T), Temperature (K), Electric Current (A), Amount of Substance (mol), and Luminous Intensity (cd).
- Derived Quantities: All other physical quantities are derived from these fundamental quantities through mathematical equations. For example, Velocity is derived from Length and Time (L/T), and Force is derived from Mass, Length, and Time (ML/T²).
Systems of Units
To measure these quantities, we use standardized systems of units:
- SI (MKS): The International System of Units is the modern form of the metric system and is the most widely used system in science and engineering. Its fundamental units are the meter (m), kilogram (kg), and second (s).
- CGS: A metric system based on the centimeter (cm), gram (g), and second (s).
- FPS (Imperial): A system based on the foot (ft), pound (lb), and second (s).
Dimensional Analysis
Dimensional analysis is a powerful tool used to check the consistency of physical equations. A physically valid equation must be dimensionally homogeneous, meaning every term in the equation must have the same dimensions. This principle helps in verifying equations and deriving new ones.
Work and Power
Work is done when a force causes displacement. In SI units, work is measured in Joules (J), where 1 Joule is the work done by a 1 Newton force over 1 meter. Power is the rate at which work is done, measured in Watts (W), where 1 Watt equals 1 Joule per second. In rotational motion, power can be calculated as the product of torque and angular velocity.
Properties of Materials
Understanding the properties of materials is fundamental to physics and engineering. This section focuses on the different states of matter and their key physical characteristics.
States of Matter
- Solid: In a solid, atoms are tightly packed in a fixed, often crystalline, structure. They vibrate in place but do not move around.
- Liquid: Molecules in a liquid are close together but can move past one another, allowing the liquid to flow and take the shape of its container.
- Gas: Gas molecules are far apart and move randomly and rapidly, filling the entire volume of their container.
Key Physical Properties
- Density (ρ): Defined as mass per unit volume (kg/m³). The density of a gas is highly sensitive to changes in pressure and temperature, while for liquids, this variation is generally small.
- Specific Weight (γ): The weight of a substance per unit volume (N/m³). It's calculated by multiplying density by the acceleration due to gravity (γ = ρg).
- Specific Gravity (SG): A dimensionless quantity that is the ratio of a fluid's density to the density of a reference substance, typically water at 4°C. (SG = ρ / ρ_water).
- Viscosity (μ): A measure of a fluid's resistance to flow, often thought of as its "thickness." It describes the internal friction of a moving fluid.
- Dynamic (Absolute) Viscosity: Measures the fluid's resistance to shear flow. Its SI unit is Pascal-second (Pa·s).
- Kinematic Viscosity (ν): The ratio of dynamic viscosity to density (ν = μ/ρ). Its SI unit is m²/s. The relationship between different units like Poise, Centipoise, Stoke, and Centistoke is important in calculations.
Stoke's Law
Stoke's Law describes the viscous drag force experienced by a spherical object moving through a viscous fluid. The force depends on the viscosity of the fluid, the radius of the sphere, and its velocity. When an object falls through a fluid, it reaches a terminal velocity where the drag force plus the buoyancy force equals the gravitational force.
Heat Transfer
Heat transfer is the exchange of thermal energy between physical systems. Understanding its mechanisms is crucial for industrial processes and energy management.
Temperature and Heat
- Internal Energy (U): The total kinetic and potential energy of all particles within a system.
- Temperature: A measure of the average kinetic energy of the particles. It determines the direction of heat flow.
- Heat (Q): The energy transferred from a hotter object to a colder one. The amount of heat required to change an object's temperature is given by Q = mcΔT, where 'c' is the specific heat capacity.
Mechanisms of Heat Transfer
- Conduction: Heat transfer through direct molecular collision. No material is exchanged. Governed by Fourier's Law, which relates heat flux to the thermal conductivity and the temperature gradient.
- Convection: Heat transfer through the movement and circulation of fluids (liquids or gases). Hotter, less dense fluid rises, and cooler, denser fluid sinks. This is described by Newton's Law of Cooling, using a heat transfer coefficient (h).
- Radiation: Heat transfer via electromagnetic waves (like infrared). It requires no medium and can occur through a vacuum. The rate is determined by the Stefan-Boltzmann Law (Q = AσεT⁴), where ε is the emissivity of the surface.
Phase Change and Latent Heat
During a phase change (e.g., solid to liquid), the temperature of a substance remains constant despite the addition of heat. This energy is called Latent Heat (L).
- Latent Heat of Fusion (L_f): Energy required to melt a solid to a liquid.
- Latent Heat of Vaporization (L_v): Energy required to vaporize a liquid to a gas.
The Heating Curve of Water is a classic example that plots temperature against heat added, showing plateaus during the melting of ice and the boiling of water.
Physics Comprehensive Quiz (105 Questions)
Test your knowledge with 105 questions covering all parts of the curriculum, including lecture notes, exams, and problem sheets.