Physics Chapter 1: Units and Dimensions

Definition of Physics and Physical Quantities

• Physics explores nature and the properties of matter and energy including heat, light, sound, and electricity.
• The study emphasizes measurement accuracy and uses scientific methods for verification through experiments.
• Physical quantities are measurable aspects such as distance, speed, mass, and force.
• Applied Physics bridges the gap between physics and engineering by solving human problems.

Units: Fundamental and Derived Units

• Measurement involves comparing unknown quantities with known fixed quantities.
• A unit is a standard known quantity used for measurement like meter for length.
• The expression for physical quantity can be generalized as:
  • Q = n × u
  • Where Q is Physical Quantity, n is Numerical value, and u is Standard unit.
• Standard units should be well-defined, consistent across conditions, appropriately sized, reproducible, and internationally accepted.

Classification of Units

• Fundamental Units: Independent quantities measured directly, such as:
  • Mass: Kilogram (Kg), Gram, Pound
  • Length: Meter, Centimeter, Foot
  • Time: Second
• Derived Units: Quantities derived from fundamental ones, e.g.:
  • Area: Length × Length
  • Speed: Distance / Time

Systems of Units

• C.G.S. System: Length is measured in centimeters, mass in grams, time in seconds.
• F.P.S. System: Length in feet, mass in pounds, and time in seconds.
• M.K.S. System: Length in meters, mass in kilograms, and time in seconds.
• S.I. System: International System of Units that expands M.K.S. to include units for electric current, heat, etc.

Energy Transformation

• Energy can change forms (e.g., heat to mechanical energy in engines, electrical energy to light in bulbs).
• Examples of transformations:
  • In electric motors, electrical energy converts to mechanical energy.
  • In dams, potential energy converts to kinetic energy.

Kinetic Energy

• Defined as energy possessed by an object due to its motion.
• Formula for kinetic energy (K.E.):
  • K.E. = 1/2 mv²
  • This is derived from force acting over a distance.
• Examples include running water, wind energy, and moving objects like bullets.

Potential Energy

• Energy stored in an object due to its position, expressed as potential energy (P.E.).
• Moment of Inertia (I) relates to a body's mass and radius of gyration (K):
  • I = MK²
• Radius of gyration quantifies distribution of mass around an axis.

Temperature

• Defined as the average kinetic energy of molecules in a body.
• Units of temperature include Fahrenheit (°F), Celsius (°C), and Kelvin (K), with Kelvin as the S.I. unit.

Difference Between Heat and Temperature

• Heat:
  • Energy transferred between bodies due to temperature difference.
  • Total kinetic energy of molecules.
  • Depends on the quantity of matter; measured in Joules.
• Temperature:
  • Measure of an object's hotness or coldness.
  • Average kinetic energy; does not depend on the quantity of matter.
  • Measured in Kelvin.

Principles of Temperature Measurement

• Temperature measurement is based on the fact that material properties change with temperature.
• Thermometers are devices that utilize physical or chemical properties to measure temperature.
• Types of thermometers include:
  • Mechanical (liquid-in-glass, bimetallic, etc.)
  • Thermo-electric (thermocouples)