Universal Motion

• Aristotle - born in 384 BC, Macedonia Greece
• Aristotle - "all objects on Earth were a mixture of 4 elements (air, earth, water, fire)"
• Aristotle's Theory of Motion - believed Earth to have different set of motion laws to outer space

  • Outer Space: motion is perfect, eternal, and unchanging because it's circular
  • Earth: motion is chaotic and imperfect (elements mix to make various substances and would want to be pure and separated again)
• Types of Motion to (Aristotle)

  1. Natural Motion
  2. Violent Motion
• Natural Motion - any type of motion that a body does naturally w/o forcing the motion to happen; either straight up/down, happens spontaneously
• Violent Motion - when a motion requires force to make an object move in an "unnatural" manner; action necessary to move things horizontally, doesn't happen w/o action
• 4 Theories of Motion

  1. Objects of "Earth" material falls toward the center of the Earth because it seeks its natural place
  2. Heavy objects fall faster than lighter ones
  3. Objects fall faster in air than in water
  4. Objects sometimes move away from their natural places
• Galileo - born in Pisa, Italy (1564-1642), disproved Aristotle's claims, studied medicine at the University of Pisa, and then changed to mathematics
• 2 objects (light and heavy) dropped from the Tower of Pisa fell and struck the Earth at the same time (regardless of mass)
• Marble made to roll on a flat surface (w/ absence of friction) would roll forever
• Marble rolled down on an inclined plane at a fixed angle, the ratio of the distance covered to the square of the corresponding time was constant (hence, m/s^2 was born)
• Gravitational force of Earth on a free-falling object causes the object to uniformly accelerate as it falls down towards the surface (distance covered to the square of the corresponding time was constant as well)
• Types of Motion (Galileo)

  1. Horizontal Motion
  2. Vertical Motion
  3. Free Fall Motion
  4. Vertical Upward Motion
  5. Projectile Motion
• Horizontal Motion - object in motion will remain in motion if unobstructed and external force is unnecessary for it to remain in motion
• Vertical Motion - with resistance absent, objects will fall depending on gravity and their time of fall; if resistance is present, objects will slow down and reach a uniform motion until reaching the bottom and stop.
• Free Fall Motion - type of motion under the sole influence of gravity

  • Examples:

  1. dropped from rest
  2. thrown vertically upward
  3. thrown upward at an angle to the horizontal (projectile)
• Important Free-Fall characteristics:

  1. Free-falling objects do not encounter air resistance
  2. All free-falling objects (on Earth) accelerate downward at 9.8 m/s^2
• Vertical Upward Motion - motion that follows a vertical upward path resisting the effect of acceleration due to gravity (when you throw smthn upward, you oppose gravity=vertical upward motion)
• Projectile Motion - combination of uniform motion in the horizontal direction and uniformly accelerated motion in the vertical direction (will continue to move w/o an applied force, if not impeded)