The Ordered Universe Chapter 2: Newton's Laws of Motion and Gravity

The Night Sky

• Movement of stars, planets, sun

• Key for survival of ancestors

• Astronomy as the first science

• Ancient observers believed physical events are quantifiable and predictable

Stonehenge

• Started in 2800 B.C.

• Built over a long time by different peoples

• Marks passage of time, specifically the seasons

• Still functions today

The Birth of Modern Astronomy

• Historical Background: Ptolemy & Copernicus

  • Ptolemy: First planetary model with Earth at the center

  • Copernicus: "On the Revolutions of the Spheres" with the Sun at the center

• Observations: Tycho Brahe & Johannes Kepler

  • Tycho: Observed new star, showed heavens can change, collected data on planetary movement

  • Kepler: First Law - Planets have elliptical orbits

The Birth of Mechanics

• Galileo Galilei

  • Mechanics: motions of material objects

  • Supported Copernicus' view

• Speed, Velocity, and Acceleration

  • Equations for speed and velocity

• Relationship among distance, time, velocity, and acceleration

• Galileo's experiments on falling objects

• Constant acceleration and freefall

Isaac Newton and the Universal Laws of Motion

• The First Law: Objects in motion stay in motion, objects at rest stay at rest unless acted upon by an unbalanced force

• The Second Law: Force is proportional to mass and acceleration (F=ma)

• The Third Law: Interacting objects exert equal but opposite forces upon each other

Momentum

• Motion depends on mass and speed

• Linear momentum equation: p=mv

• Law of conservation of linear momentum

• Angular momentum

The Universal Force of Gravity

• Newton's law of universal gravitation: F=Gm1m2/d^2

• The Gravitational Constant, G: G=6.67 x 10^-11m^3/s^2-kg or 6.67 x 10^-11N-m^2/kg^2

• Weight and Gravity: Weight depends on gravity, mass is constant

• Big G and Little g: Force=(G x mass x ME)/RE^2, g=(G x ME)/RE^2, 9.8 N-kg = 9.8m/s^