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Module 1 Slides

MODULE 1: The Physical World

  • Date: September 3, 2024

WHAT IS THE PHYSICAL WORLD?

Historical Models

  • Classical Greece: Geocentric model

    • Earth viewed as spherical, motionless, positioned at the universe's center

    • Key observation: Sun appears to revolve around Earth daily

  • Aristarchus: Introduced the Heliocentric model

    • Proposed that Earth, while spherical and motionless, revolves around the Sun

  • Stellar Parallax: Investigates the apparent shift of stars due to Earth's movement.

Geocentric Model Characteristics

  • Perfect Circular Orbits: Assumes celestial bodies follow perfect circles.

  • Uniform Speed: Bodies move at a constant speed.

  • Earth remains at the center, emitting no apparent movement.

Heliocentric Ideas and Developments

Hipparchus: Precession of the Equinoxes

  • Definition: Every 26,000 years, Earth's axis completes a circular rotation, changes the North Star from Polaris to Vega.

    • Significance: Astronomy's understanding of star position changes over millennia.

Eratosthenes: Measurement of Earth's Circumference

  • Method: Used shadows in two locations (Alexandria and Syene) to calculate Earth's size based on sun's position.

Ptolemic Model Insights

Retrograde Motion

  • Definition: Apparent reversal of the direction of a planet's motion in the sky.

    • Observation of Mars depicted in diagrams showing movement against the celestial sphere.

  • Ptolemy proposed a complex model to account for this motion based on various orbits.

Advances in Astronomy

Galileo Galilei

  • Utilized telescope advancements to observe craters on the moon and celestial bodies.

    • Supported Copernicus' heliocentric theory.

Johannes Kepler (17th century)

  • Introduced concepts of Elliptical Orbits, refining celestial mechanics.

  • Isaac Newton later described these orbits based on gravitational laws.

INTRODUCTION TO GRAVITY

Newton's Laws of Motion

  1. First Law: An object remains at rest or in uniform motion unless acted upon by a force.

  2. Second Law: F = ma (Force equals mass times acceleration).

  3. Third Law: For every action, there is an equal and opposite reaction.

Understanding Weight Variations

  • Normal Weight: Weight under standard gravity.

  • Greater than Normal Weight: Increased gravitational effects.

  • Zero Weight: Achieving weightlessness.

Newton's Law of Universal Gravitation

  • Formula: Fg = G(m1m2)/r²

    • Where G is the gravitational constant (6.67430 × 10^-11 N·m²/kg²).

  • Centripetal Force: Related to objects in a circular path.

Einstein's Contribution

General Theory of Relativity

  • Illustrates how mass bends space-time, affecting gravity and motion of celestial bodies.

REFERENCE SYSTEMS IN PHYSICAL WORLD

Reference Point Concepts

  • Earth: Can serve as a reference for spatial movement.

  • Observation Perspective: Depending on the frame (train vs. surrounding trees), movement seems different.

MODEL-DEPENDENT REALISM

  • Concept highlights the use of models to understand the universe.

  • Quantum Physics: Introduction of 'quanta' as theoretical components defining light's nature.

UNDERSTANDING THE PHYSICAL WORLD: Models, Theories, and Laws

Definitions

  • Model: A simplified representation of reality.

  • Theory: Explanation of observed phenomena.

  • Law: Statements based on repeated experimental outcomes.

Characteristics of a Good Model

  • Elegance and simplicity

  • Predictive capacity: Works with existing observations and forecasts future phenomena.

Characteristics of a Good Theory

  • Logical consistency

  • Quantitative predictions

  • Reliability upon repeated experiments

COSMOLOGICAL EVENTS

Big Bang and Cosmic Evolution

1- 10^-32 seconds: Origin of fluctuations in the universe.

  • 1 year to 1 billion years: Formation of structures leading to the first stars and galaxies.

  • 13.82 billion years: Current state of galaxy clusters and cosmic structures.

SCIENTIFIC MEASUREMENT

Branches of Science

  • Elementary Particles: Studies under Particle Physics.

  • Atomic Nucleus: Analyzed via Nuclear Physics.

  • Atoms & Molecules: Relevant to Chemistry.

  • Biological sciences approach the study of larger entities like plants and animals.

SCIENTIFIC METHOD

Steps Involved

  • Formulate theories

  • Gather facts and make observations

  • Identify patterns and develop hypotheses

  • Conduct tests and further refine theories.