motion

• Uniform motion is when an object covers equal distances in equal intervals of time.
• Displacement


  • Distance moved in a particular direction
  • Measure of change of position
  • Displacement = final position – initial position
• Vector quantities

  • Displacement
  • Velocity
  • Acceleration
  • Weight
  • Forces
• Speed

  • Distance travelled per unit time
  • Speed is a rate which shows the change of distance with time
• Units for speed

  • Metre per second (m/s)
• Scalar quantity


  Quantity that has a magnitude but no direction
• Distance


  Total length travelled by an object
• Instantaneous speed

  Speed at any instant
• Units for distance

  • Millimetre, centimetre, metre, kilometre
• Converting m/s to km/h

  Multiply the value by 3.6
• Parameters of motion

  • Identify parameters of motion as vectors or scalars
  • Analyse straight-line motion under constant acceleration graphically, numerically and algebraically
  • Analyse graphically non-uniform motion in a straight line
• Vector quantity


  Quantity that has magnitude and direction
• Instantaneous speed is the speed at any instant, e.g., the speedometer in a vehicle shows the speed at a particular instant
• Converting km/h to m/s

  Divide the value by 3.6
• Other terms

  • Instantaneous speed: speed at any instant, e.g. the speedometer in a vehicle shows the speed at a particular instant
  • Constant speed: travelling at the same distance per unit time throughout, steady rate, same distance covered at every regular interval of time
  • Average speed: the total distance travelled divided by the total time taken
• Displacement-time graphs: Also known as a position-time graph. Indicates the position of an object at any time for motion that continues over an extended time interval. A: moving away from start point, B: moving away from start point, C: moving back to start point (km)
• Velocity

  Distance travelled per unit time in a specific direction, rate of change of displacement, Vector quantity, SI unit: metre per second (ms-1)
• Distance-time graphs: Gradient = Speed of an object. The steeper the line, the greater the speed
• ‘+’ and ‘−’ signs show the directions of motion
• Displacement-time graphs: Gradient indicates the velocity of the object. Can be positive or negative. Positive velocity indicates movement in a positive direction. Negative indicates movement in a negative direction (km)
• Velocity


  Displacement divided by time taken
• Converting from kmh-1 to ms-1

  Divide the value by 3.6
• Converting from ms-1 to kmh-1

  Multiply the value by 3.6
• Instantaneous velocity

  • Velocity of an object taken at a specific time, an instant
  • Gradient of displacement-time graph: velocity of an object
  • Tangents: used to determine the velocity of an object at any instant
  • Tangent: a straight line that touches a curve at only one point
  • Each tangent on a curve has a unique gradient, which represents the instantaneous velocity at that point
• Acceleration can mean that the object is slowing down (i.e. velocity is decreasing) or the object is speeding up in the opposite direction
• Velocity-time graphs

  • Gradient of graph: Acceleration of object
  • Area under graph: displacement of object
• Increasing velocity

  • Speeding up
  • Tangent of slope = instantaneous velocity
• Increasing velocity

  • Uniform or constant acceleration
  • Acceleration: gradient of v-t graph
• Velocity

  • Object moving at uniform negative velocity
  • Object moving in the opposite direction
  • No acceleration
• Negative acceleration

  • Object slowing down
  • Object speeding up in negative direction
• Decreasing velocity


  • Slowing down
  • Tangent of slope = instantaneous velocity
• Time

  • Object moving at uniform negative velocity
  • Object moving in the opposite direction
  • No acceleration
• Linking motion graphs

  • Displacement vs. time
  • Velocity vs. time
  • Acceleration vs. time
  • Area under curve
• Velocity

  • Object moving at uniform positive velocity
  • Object moving in the positive direction
  • No acceleration
  • Object at rest
  • No displacement
  • No velocity
  • No acceleration
• If the area is below the time axis, it indicates a negative displacement
• Gradient, g = 9.8 ms^-2 velocity
• If they are released from the same height, they will reach the ground at the same time
• A falling object can only be in free fall if there is no air resistance
• Gradient, g = 9.8 m/s^2 acceleration of free fall g is 9.8 m/s^2 for all objects
• When an object is free falling under the earth’s gravitational pull, its speed steadily increased and it experiences constant acceleration