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.