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• Pythagoras introduced the idea of the round model of the earth

  6th century BC
• Stonehenge


  A big computer that early people used to calculate the position of planets and the sun
• Modern Evidence Supporting Spherical Earth Model


  • Spacecraft Photos: Satellite photos show that the earth is plainly spherical
  • Astronauts in satellites orbiting in low Earth orbit personally observed curvature of the planet
• Lunar Eclipse


  • The shadow of the earth formed on the one side of the moon shows a dark circle
  • The shape that casts in the moon shows a spherical shape
• Time Zones


  • The time difference in different places in the world is due to the presence of a time zone
  • It can only be explained if the world is round and continuously rotating on its axis
• Riding a Plane


  • Airplanes are capable of traveling in a straight line without falling off any edges even for a period of time
  • It can circle the earth without stopping
  • The curvature of Earth on the horizon is noticeable if you travel in transatlantic flight
• The Nebra sky disk, collected from Northern Europe, was dated


  Approximately 1600 BC
• Supernova that resulted in the Crab Nebula


  1006 AD
• One of the clearest examples of early rock drawings is a petroglyph that shows the 1006 AD supernova that resulted in the Crab Nebula
• The earliest written records of astronomical observations were from the Babylonians dated 1600 BC that tried to record positions of planets and the time eclipse events.
• Hellenistic Observations The distances between the nearby planetary object were studied by Eratosthenes and Aristarchus (250 BC). Eratosthenes introduced the spherical Earth model and through the use of geometry, he tried to calculate the circumference of the earth.
• Hellenistic Observations Plato first introduced that the planets follow perfect circular orbits around the earth. During the Hellenistic era, Earth is believed to be the center of the Universe.
• Heraclides (330 B.C.) presented the first Solar System model where the earth is the center. It is called the geocentric solar system model
• Aristarchus (270 B.C.) presented an alternative model of the Solar System placing the sun at the center. This model was termed as the heliocentric theory. He was the first to propose the sun as the center of the universe.
• Kepler’s Works

  • The planet’s path around the sun is elliptical in nature where the sun is the center and located at one focus.

  • There is an imaginary line from the center of the sun to the planet and this sweep out equal areas within equal time intervals.

  • The ratio of squares of the periods between any two planets will always be equal to the ratio of the cubes of its distances from the sun.
• Aristotle’s view on the motionwas based on his observations, which made his ideas acceptable and stood for many years.
• Motion is an object’s change in position with respect to time.
• Natural motion occurs when an object moves and returns to its natural state depending on the object’s composition.
• Violent motion occurs when an object moves after an external force, such as pushing or pulling, is applied.
• Aristotle believed that the vertical motion of an object depends on the kind of element that makes up the object.
• Aristotle explained that horizontal motion is caused by force. This force is what Aristotle referred to as the impetus.
• Aristotle believed that projectiles moved parallel to the ground until it was the object’s time to fall toward the ground.
• Acceleration is defined as the rate of change of velocity.
• The law of inertia states that if no net forces act on an object, then the velocity of the object will remain unchanged.
• Galileo Galilei discovered that objects continue moving at constant speed unless acted upon by another force.
• HORIZONTAL MOTION According to him, if the Earth’s surface is very flat and extends infinitely, objects that are pushed will not be impeded. Thus, the objects will continue to move.
• PROJECTILE MOTION Galileo believed that projectiles follow a curved path called a trajectory.
• GALILEO’S INCLINED PLANE EXPERIMENT

  This change in speed per unit time is called acceleration. He postulated that objects fall with uniform acceleration.
• INERTIA is defined as the tendency of matter to resist a change in its state of motion. It is dependent on the mass of an object. A more massive object has greater inertia.
• LAW OF INTERACTION The law of interaction states that when an object exerts a force on another object, the second object exerts another force that is equal and opposite in direction. These forces are called action–reaction pair.
• Light is a form of electromagnetic radiation that is visible to the human eye. It consists of photons, which are elementary particles that travel in waves.
• Christiaan Huygens and Isaac Newton were pioneering figures in the study of light
• REFLECTION - It is the bouncing of light when it reaches a reflecting surface or a boundary between two media.
• Incident ray refers to the ray of light that hits the reflecting surface/boundary.
• Refracted ray refers to the ray of light that bounces back.
• Normal line is a line perpendicular to the reflecting surface.
• Angle of incidence and angle of reflection are the angles formed by the incident ray and the reflected ray, respectively, with the normal line.
• LAW OF REFLECTION The angle of incidence, the angle of reflection, and the normal line lie on the same plane.
• PARTICLE NATURE OF LIGHT In most instances, light is usually described as a wave since it is part of the electromagnetic wave.
• But when light is shone on a metal surface, there is an emission of free electrons. This phenomenon is called the Photoelectric effect.