W2

• Motion


  Change of position of an object with respect to time
• Types of motion


  • Natural motion
  • Violent motion
• Natural motion


  • A body will move and will return to its original state based on its composition
• Violent motion


  • Needs external force for it to move
• Vertical motion


  Natural motion, falling or rising
• Examples of vertical motion


  • A ball falls even when thrown upward
  • Smoke always goes up
• Horizontal motion


  Violent motion, requires push or pull to maintain
• Example of horizontal motion


  • Piled boxes of food donations remain on the floor unless a push or pull force is applied
• Projectile motion


  Combination of natural and violent motion
• Aristotle believed projectile motion is parallel to the ground until the object falls back
• Aristotle believed the heavier the object, the faster it falls
• Galileo countered Aristotle's claims and stated that motion can be described by measurement and changes in quantifiable variables like time and distance
• Galileo's view on vertical motion

  • In the absence of air resistance, objects would fall not depending on their weight, but in the time of fall
  • If an object encounters a resistive force from a fluid equal to or greater than its weight, it will slow down and reach a uniform motion until it reaches the bottom and stops
• Without any resistance, a 1-kg object will be as fast as a 10-kg object when falling because they fall within the same amount of time, given that they are released from the same height
• Galileo's view on horizontal motion

  • An object in motion, if unimpeded, will continue to be in motion, and an external force is not necessary to maintain the motion
• Example of horizontal motion


  • If a ball is pushed on an infinitely flat plane, the ball will continue to roll if unimpeded
• Galileo was able to determine that the path of a projectile is parabolic
• Acceleration


  A vector quantity that is defined as the rate at which an object changes its velocity
• Uniform accelerated motion


  Velocity change is constant
• Free fall


  Objects that fall through a vacuum are subjected to only one external force, the gravitational force, expressed as the weight (w) of the object
• On Earth, the value of g is 9.8 m/s2
• Proving Galileo's Law of Free Fall


  1. In Newton's 2nd Law of Motion, force (F) is equal to mass (m) x acceleration (a)

  2. By transposition, we can solve for acceleration (a)

  3. For a free-falling object, the external force is the weight of the object

  4. If we substitute these to the formula for acceleration (a), we get: a = g
• Mass, size, and shape are not factors in describing motion of an object
• Inertia


  The tendency of materials to resist change in their state of motion
• No force is needed for an object to continue moving, inertia prevents it from stopping
• Newton's First Law of Motion

  Every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force
• Examples of Newton's First Law


  • If there is no net force acting on an object, it will maintain constant velocity
  • If the velocity is zero, the object remains at rest
  • If external force is applied, velocity will change because of the force