chap 2 - kinematics

• instantaneous velocity = velocity at a particular moment in time
• to find instantaneous velocity, find a smaller displacement over shorter time interval
• free fall objects are subjected to a constant acceleration due to gravity because of earth´s attraction
• uniform acceleration

  • constant rate of change of velocity
  • acceleration = final velocity- initial velocity / time at which an object is at final velocity- initial velocity
  • unit time is the same
  • increase/decrease at a constant rate
• non-uniform acceleration

  • occurs when the change (increase or decrease) in velocity per unit time is the same
• speed -time graph (area under graph)

  • to find distance of graphs, calculate the area under a speed-time graph over the period of time
• zero acceleration=constant speed / not moving / stationary
• speed-time graph - gradient=acceleration
• distance-time graph

  • gradient=speed
  • speed is given by the gradient of a distance-time graph
• • when an object is experiencing decreasing acceleration, its speed continues to increase but at a slower rate.
  • when an object decelerates, its speed decrease
• velocity

  • rate of change of displacement
  • velocity = displacement / time taken
  • vector quantity --> have both magnitude and direction

  --> measured in a specific direction

  • SI unit : metre per second (m s⁻¹)

  average velocity

  • total displacement/total time taken

  > constant speed in same direction = constant velocity

  > constant speed in different direction = velocity changed
• acceleration

  • rate of change of velocity increases (positive acceleration ) or decreases (decreasing acceleration )
  • acceleration = change in velocity / time taken
  • vector quantity
  • SI unit : metre per second (m s⁻²)
• deceleration

  • when velocity decrease (retardation)
• distance-time graph (object at rest)

  • when graph is horizontal, there is zero gradient
  • distance is constant for every second
• distance-time graph (object at uniform <constant> speed)

  • steepness of graph= straight line with constant gradient
• distance-time graph ( object at increasing (non-uniform) speed

  • increasing gradient = speed increases uniformly
• distance- time graph (object at decreasing <non-uniform> speed)

  • decreasing gradient = speed decreases
• speed time graph (object at uniform speed)

  • horizontal straight line = zero acceleration
• speed-time graph (increasing acceleration)

  • increase in speed increases with time
  • positive and increasing gradient
• speed-time graph (uniform acceleration)

  • positive and constant gradient = constant gradient and constant acceleration
• speed-time graph (uniform deceleration)

  • negative and constant gradient = decreasing speed (constant deceleration)
• • speed-time graph

  positive and decreasing gradient = decreasing acceleration = change of speed per unit time decreases
• scalar qualities

  • only have magnitude
  • eg : distance, speed, mass, energy

  vector quantities

  • both magnitude and direction
  • eg: displacement, velocity, acceleration
• distance

  • total length covered by moving object, along the path taken
  • direction of motion does not matter
  • SI unit : metre (m)
• speed

  • distance moved per unit time
  • speed = distance travelled / time taken
  • scalar quantity
  • SI unit : metre per second (m s ⁻¹)

  average speed

  • total time includes rest time
• speed-time graph (decreasing deceleration )

  • increase in speed decreases with time
  • positive and decreasing gradient
• speed-time graph (object at rest)

  • horizontal line at x-axis
• object falling without air resistance (free fall)

  • only happens in vacuum (no air resistance)
  • only force acting is weight
  • direction of force and motion is downward towards the centre of the earth
  • objects falling without air resistance experiences a constant increase in speed under earth´s gravity
  • acceleration due to gravity us constant
  • velocity speed time graph has a constant gradient
  • not dependent on the mass or size of object