MOTION

• Speed of light


  3 × 10^8 meters per second
• Aristotle

  • Born in 384 BC in Macedonia, Greece
  • Believed all objects on Earth were a mixture of 4 elements
  • Believed the laws governing the motion of the heavens were different from those that governed motion on Earth
• Aristotle's theory of celestial motion

  The motion of the celestial bodies is circular because this is the most perfect kind of unchanging eternal motion. Since there is perfection in the heavens, there can be no change, except for heavenly motions. The heavenly motions were part of the heavenly perfection and so by definition were NOT changes, but a type of constancy (hence the necessity for uniform circular motion.)
• Aristotle's theory of sublunar realm

  Described Earth as chaotic and imperfect; the pure (perfect) elements, earth, air, fire, and water, find themselves combined into the variety of substances in the physical world. These mixtures (imperfect substances) would want to be separated to become pure and perfect again.
• Natural motion


  Exists in any type of motion that a body does naturally without forcing the motion to happen
• Aristotle's 4 theories of motion

  • An object which is made up of an "Earth" material, falls toward the center of the Earth because it seeks its natural place.
  • Heavy objects fall faster than the lighter ones.
  • Objects fall faster in air than in water.
  • Objects sometimes move away from their natural places.
• Horizontal motion


  Not natural for Aristotle
• Violent motion


  Exists when a motion requires a force to make an object move in an "unnatural" manner
• Impetus


  Aristotle's concept of the force that keeps an object in violent motion
• Natural motion

  Either straight up or straight down, happens spontaneously
• Longevity of Aristotle's theory of motion

  • Consistent with common sense
  • No other theories about motion were available during Aristotle's time
  • Quantitative method of observation to prove the validity was not yet developed
• Galileo

  • Born in Pisa, Italy
  • Studied medicine at the University of Pisa and then changed to Mathematics
• Galileo disproved Aristotle's claims and believed that the motion of objects is not simply due to the composition of objects. He mentioned that motion can be described by mathematics and the changes in some physical variables such as time and distance.
• Galileo's findings about horizontal motion


  • An object in motion will continue to be in motion if unobstructed
  • An external force is not necessary for it to maintain the motion
  • Prelude of the law of inertia
  • A marble made to roll on a flat surface would roll for an infinite amount of time
• Galileo's findings about vertical motion


  • In the absence of a resistance, objects would fall not depending on their weight, but in the time of fall
  • If the object encounters a resistive force from a fluid equal or greater than its weight, it will slow down and reach a uniform motion until it reaches the bottom and stops
  • A stone dropped in the ocean will sooner or later travel at a constant speed
  • The two objects (light and heavy), dropped simultaneously from the tower of Pisa, fell and struck the earth at the same time
• Galileo's findings about free fall motion


  • type of motion under the sole influence of gravity
  • Free-falling objects do not encounter resistance
  • All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s^2 (often approximated as 10 m/s^2)
  • The gravitational force of the earth on a freely falling object to be uniformly accelerated as it goes toward the surface of the earth. The distance covered to the square of the corresponding time was always the same.
• Galileo's findings about vertical upward motion


  • Follows a vertical upward path resisting the effect of acceleration due to gravity
• Galileo's findings about projectile motion


  • Galileo believed that a projectile is a combination of uniform motion in the horizontal direction (Vx) and uniformly accelerated motion (Vy) in the vertical direction. If it is not impeded, it will continue to move even without an applied force.
• Isaac Newton's Laws

  He concluded that earth is attracted to apples and the apple is also attracted to earth. Thus, he formulated universal gravitation and laws of motion.
• Law of Inertia

  An object at rest remains at rest, and an object in motion remains in motion with the same velocity unless acted upon by an unbalanced force.
• Law of Inertia


  • vase in a room
• Difference between Galileo's assertion and Newton's Law of Inertia

  The difference lies in the concept of force.
• Galileo


  Knew about friction but did not know about the concept of force. He used the term 'push and pull' to signify forces.
• Sir Isaac Newton


  Was the one who defined the concept of force and its relation to motion.
• Law of Acceleration

  Acceleration is directly proportional to the force applied on an object and inversely proportional to the mass of an object.
• Law of Acceleration

  • force, mass, acceleration
• As the mass in the cart increases

  The more force we have to exert for the cart to move.
• Law of Interaction

  For every action, there is an equal and opposite reaction.

  Whenever one body exerts a force on a second body, the second body exerts a force back on the first that is equal in magnitude but opposite in direction
• Action force and reaction force is equal in magnitude but in opposite directions
• Law of Universal Gravitation


  Every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
• G is the gravitational constant, given by G=6.673 x 10^-13 N·m^2/kg^2. Newton's law of gravitation applies universally.
• BALANCED FORCES

  all forces acting on the object is equal

  there is no force left on the object

  Fnet = 0
• Law of Inertia

  • Force of chair upward on you -> Weight (Force of Earth downward on you)
  • A spacecraft keeps going because no forces act to stop it.
• Force, Mass, Acceleration

  • a = F/m
  • If we double the force, we double the acceleration.
  • If we double the mass, we half the acceleration.
• Law of Acceleration

  • The same force exerted on a larger mass produces a correspondingly smaller acceleration.
• Law of Acceleration

  • Pushing a vehicle
  • Pulling a big rock above the table