Greek Views of Matter and Motion

Lesson 14.1 - Greek Views of Matter and Motion

• The objectives are to discuss Greek's early beliefs on motion and matter and to explain early observable non-terrestrial motion.

Early Views on Matter - Empedocles

• Empedocles, a Greek philosopher who lived from 492 BCE to 432 BCE, proposed that all things consist of four elements: fire, air, water, and earth.
• The combination and ratio of the four elements determine matter's properties.

The Existence of Atoms - Democritus

• Democritus(460 BCE - 370 BCE) coined the term atomos, meaning indivisible, for small pieces of matter.
• Atoms are eternal and indestructible.
• Atomos are specific to their constituent material.

The Modern Atomic Theory - John Dalton

• John Dalton (1766-1844), a British scientist, developed he first version of the Atomic Theory.
• Matter is composed of tiny particles.
• All matter consists of atoms.
• All atoms of an element are identical.
• Atoms are indestructible and unchangeable.
• Elements react to form compounds in defined ratios.

Aristotle's View on Motion

• Aristotle (384-322 BCE) introduced the concept of motion.
• There are two forms of motion: natural and violent.
• Natural motion leads objects to move upward and downward due to the matter's weight.
• Heavier things fall faster than lighter things.
• Violent motion results from pushing or pulling caused by humans, and is voluntary or involuntary.
• Violent motion requires force to occur, such as throwing a ball.

Galileo's Law of Motion

• Galileo Galilei (1564-1642) stated that all bodies move and accelerate regardless of size and mass.
• Key observations are: a concept of velocity using inclined planes, force idea that causes the motion of an object, being at rest is the natural state of an object, inertia is resistance of an object to changes in motion.

Newton's Laws of Motion

• Isaac Newton (1642-1727) defined the relationship between motion and energy.
• The principle of acceleration is a change in velocity induced by force.
• Inertia is the resistance to a velocity change that is proportional to an object's mass.
• Momentum is the quantified motion energy that equals mass multiplied by velocity.
• Newton's Three Laws of Motion include:
  • All objects remain at rest or in uniform motion unless acted upon by an external force.
  • Object's velocity changes when subjected to an external force.
  • An action force has an equal and opposite reaction force.

Early Observable Nonterrestrial Motion - Diurnal Motion

• Diurnal motion refers to the apparent movement of stars and other celestial bodies around Earth.
• Earth's rotation causes it from west to east.
• Without Earth's spin, stars wouldn't appear to move westward, and there would be no diurnal motion.

Annual Motion

• Annual motion refers to sun's apparent yearly movement across star background.
• This movement is caused by the revolution of Earth.
• The ecliptic is projected pathway of sun in relation to stars.
• The zodiac appears as the sun is seen through the ecliptic, consisting of 12 ancient constellations.

Precession

• Precession refers to conical motion of Earth's axis as it spins.
• Earth's axis shifts slowly, completing once cycle about every 26,000 years.
• Axial precession is caused by gravity that continuously changes planetary object's rotational axis orientation.

Lesson 14.2 - The Spherical Earth

Flat Earth Model

• The flat earth model is an old belief that Earth is a plane or discoidal form.
• Early Egyptians, Mesopotamians and Homer (Greek philosopher) believed the world was a disk in the ocean.
• Israelites thought Earth was a disc floating in water divided from heavens by arched bowl.
• Israelites believed sky was a solid dome, with sun,moon, and other planetary objects embedded in it.

History of the Spherical Earth Model

• Pythagoras introduced the idea of round model of earth in the 6th century BC.
• Anaxagoras (430 BCE) during lunar eclipse, observed earth's circular shadow reflected on the moon's surface.
• Around 340 BCE, Aristotle listed arguments for a spherical Earth: The Earth was also spherical as the moon and sun. The North Star is nearer the horizon for those nearer the equator. When a ship sailed, the hull disappeared first, implying the surface of Earth was curved.
• Around 240 BCE, Eratosthenes attempted to calculate earth's circumference.
• A stick cast no shadow in Syene, Southern Egypt during the summer solstice. In Alexandria, he determined the angle sun rays made versus vertical stick cast.
• In Alexandria, the sun makes a 7.2° angle to the vertical. In Syene, it is 0°.
• Eratosthenes hypothesized that light rays from the sun were parallel.
• Erathostenes computed earth's circumference to approximately 250,000 stadia, or 46,250 km (1 stadia = 185 m).

Modern Evidence Supporting Spherical Earth Model - Spacecraft Photos

• Satellite photos show that Earth is spherical.
• Astronauts in low Earth orbit satellites have observed curvature of the planet.

Modern Evidence Supporting Spherical Earth Model - Lunar Eclipse

• During a lunar eclipse, the shadow of Earth is a dark circle on the moon's side.
• Shape cast on moon suggests spherical shape.

Modern Evidence Supporting Spherical Earth Model - Time Zones

• Time zones around world exist because of time zones.
• This can only be explained with a round Earth spinning continuously on its axis..

Modern Evidence Supporting Spherical Earth Model - Riding a Plane

• Airplanes travel in a straight line and are able to circle the earth.
• Curvature of the Earth is visible in transatlantic flights.