Chapter 1 Lecture Outline

Nature of Physics

  • Definition: The most basic and fundamental science.

  • Goal: To understand how everything works at its most fundamental level.

  • Scope: Encompasses the study of the universe from the largest galaxies to the smallest subatomic particles.

  • Focus: Describes the interactions of energy, matter, space, and time to uncover the fundamental mechanisms underlying various phenomena.

Topics Covered in PHYS 220 (Physics – I)

  • Key Areas:

    • Mechanics

    • Fluid dynamics

    • Momentum and Impulse

    • Force: The cause of motion

    • Work, Energy, and Power

  • Principles:

    • Pascal's law

    • Archimedes' principle

    • Continuity equation

    • Bernoulli's principle

  • Applications:

    • Kinematic equations

    • Newton's three laws of motion

    • Conservation of momentum

  • Types of Motion:

    • Linear motion

    • Rotational motion

Physical Quantities, Measurements, and Units

  • Physical Quantity: A property that can be quantified by measurement (e.g., length, time, mass).

  • Measurement: Comparing an unknown quantity with a known standard reference quantity.

  • Units: Standards that represent physical quantities (e.g., meter for length).

Old System of Units

  • Characteristics: Early units based on the human body.

  • Current Usage: Only the US, Burma, and Liberia still use this system significantly.

  • Challenges: Lack of consistency hinders commerce and scientific fields, leading to the need for a rational/common system of units.

Major Systems of Units

  • British (English) System: Widely used in the US (e.g., foot, pounds).

  • International System of Units (SI): Current international standard (Metric units) defined by MKS.

SI Units and Fundamental Quantities

  • Fundamental Units: Seven dimensionally independent units:

    • Meter (m) - length

    • Kilogram (kg) - mass

    • Second (s) - time

    • Ampere (A) - electrical current

    • Kelvin (K) - temperature

    • Mole (mol) - amount of substance

    • Candela (cd) - luminous intensity.

Measurement of Length

  • Old Reference: Based on the distance between the North Pole and the Equator.

  • New Reference: Based on the distance light travels in a vacuum during 1/299,792,458 of a second.

Measurement of Mass

  • Definition: Quantity of matter.

  • SI Unit: Kilogram (kg) defined by the fixed numerical value of the Planck constant.

Measurement of Time

  • Definition: Continuous forward flow of events; only moves in one direction.

  • SI Unit: Second (s) based on atomic clock (Cs133 atom) vibrations.

Derived Units

  • Usage: Combines fundamental units for convenience.

  • Examples of Derived Units:

    • Newton (N) = kg·m/s²

    • Joule (J) = kg·m²/s²

    • Watt (W) = kg·m²/s³

Scientific Notation and SI Prefixes

  • Purpose: Conveniently expressing very large or small numbers.

  • SI System: Based on powers of ten; different prefixes denote different powers.

  • Examples: 1,000,000 = 10⁶; 0.000001 = 10⁻⁶.

Rules for Scientific Notation

  • Exponent increases by one for each decimal place shifted left; decreases for right.

    • Example: 360,000 = 3.6×10⁵.

Conversion of Units

  • Method: Multiply the quantity by a fraction equal to 1 defined by the conversion factor.

  • Example: Convert 316 ft² to m² using conversion factors to find 29.35 m².

Significant Figures

  • Importance of precision in measurements; reflects the accuracy of measured values.

  • Examples:

    • 4.6000 (5 SF)

    • 0.0002 (1 SF)

Rules for Significant Figures

  1. Non-zero numbers are significant.

  2. Zeros between non-zero numbers are significant.

  3. Leading zeros are not significant.

  4. Trailing zeros after a decimal are significant—whole numbers with no decimal are not.

  5. Including a decimal makes trailing zeros significant.

Processing Significant Figures

  • Each of the significant figures is expressed accurately while rounding in calculations.

Error and Uncertainty in Measurement

  • All measurements involve error and uncertainty; factors include calibration issues, physical variations, instrument resolution, and human error.

Example Calculations for Uncertainty

  • Example 1: Percent uncertainty of a 5-lb bag of apples measured at 5.1 ± 0.1 lb is approximately 2%.

Error Analysis

  • Percentage Error Formula:

    • % Error = (Your Result - Accepted Value) / Accepted Value × 100.

  • Percentage Difference: Used when comparing results from different methods.

Error Propagation

  • Rule for combined measurement errors:

    • % Error in R = |n1| %x1 + |n2| %x2 + ... where ni is the power in the calculation.

Order of Magnitude Estimation

  • Provides a rough idea of the magnitude of a quantity, helpful for verification of computations.