Mechanics 1 - General Principles

Mechanics 1 - BSC 021

• Course instructor: Dr. Hewayda Elghawalby
• Course objective: To introduce basic quantities and idealizations in mechanics, explain Newton's Laws of Motion, review SI units, and demonstrate numerical calculation procedures.
• Chapter 1: General Principles

  • Chapter objectives:

    • Introduce basic quantities and idealizations in mechanics
    • Explain Newton's Laws of Motion
    • Review SI units
    • Demonstrate numerical calculation procedures

  • Chapter outline:

    • Introduction
    • Fundamental Concepts
    • Units of Measurement
    • Numerical Calculations

Introduction

• Mechanics is a branch of physical science. It examines the state of rest or motion of bodies under force.
• Three branches of mechanics: rigid-body mechanics, deformable-body mechanics, and fluid mechanics.
• This course focuses on rigid-body mechanics, which is a fundamental requirement for the study of deformable bodies and fluid mechanics.
• Rigid-body mechanics is essential for the design and analysis of various engineering components, structures, and devices.

Rigid-Body Mechanics

• Subdivided into:
  • Statics: Deals with the equilibrium of bodies at rest or moving at constant velocity.
  • Dynamics: Concerned with the accelerated motion of bodies.

Fundamental Concepts

• Basic Quantities:

  • Length: Used to locate a point in space.
  • Time: Conceived as a succession of events.
  • Mass: Measures quantity of matter to compare actions of bodies.
  • Force: Considered as a "push" or "pull" exerted by one body on another.

• Idealizations:

  • Particle: Has mass but negligible size.
  • Rigid Body: Combination of particles remaining at fixed distances both before and after loading.
  • Concentrated Force: Represents the effect of a load acting at a point on a body.

• Newton's Three Laws of Motion:

  • First Law: A particle at rest or moving at a constant velocity will remain in that state unless acted upon by an unbalanced force.
  • Second Law: A particle acted upon by an unbalanced force will experience an acceleration in the same direction and magnitude proportional to the force (F = ma).
  • Third Law: Mutual forces of action and reaction between two particles are equal, opposite, and collinear.

• Weight: Gravitational force on a particle near Earth's surface. Weight (W) = mass (m) * acceleration due to gravity (g).

Units of Measurement

• Two basic systems: English and Metric
• English system:
  • Length: feet, inches
  • Mass: slugs
  • Force: pounds
  • Time: seconds
  • Pressure: pounds per square inch
• Metric system (SI units):
  • Older form: centimeter-gram-second (cgs) system
  • More modern form: System International (SI)
    • Length: meters
    • Mass: kilograms
    • Force: newtons
    • Time: seconds
    • Pressure: pascals

Conversion of Units

• Table of conversion factors between English (FPS) and SI units for fundamental quantities.
  • 1 ft = 12 in, 5280 ft = 1 mi, 1000 lb = 1 kip, 2000 lb = 1 ton
  • Provides numerical values for conversion between units (lb to N, slug to kg, ft to m)

Numerical Calculations

• Engineering calculations often use calculators/computers
• Answers must have justified accuracy using appropriate significant figures.
• Important concepts: Dimensional Homogeneity, Significant Figures, and Rounding Off Numbers