Sp2

• Scalar quantity


  A quantity that only has a magnitude, not direction dependent
• Vector quantity


  A quantity that has both a magnitude and an associated direction
• How vector quantities are represented


  • Using vector arrows
  • The length of the arrow represents the magnitude
  • The arrow points in the associated direction
• Vector quantities


  • Velocity
  • Displacement
  • Force
• Velocity


  The speed of an object in a specific direction
• Gradient of distance-time graph

  Represents the speed
• Gradient of displacement-time graph

  Represents the velocity
• Calculating speed at a given time from a distance-time graph for an accelerating object

  1. Draw a tangent to the curve at the required time

  2. Calculate the gradient of the tangent
• Calculating distance from a velocity-time graph

  It is equal to the area under the graph
• Gradient of velocity-time graph

  Represents the acceleration
• Typical value for speed of sound
• Typical value for human walking speed
• Typical value for human running speed
• Typical value for human cycling speed
• Approximate value for acceleration of an object in free fall under gravity near the Earth's surface
• Resultant force


  The single force that is equivalent to all the other forces acting on a given object
• Newton's first law for a stationary object


  If the resultant force on a stationary object is zero, the object will remain at rest
• Newton's first law for a moving object

  If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction)
• Newton's Second Law


  • Resultant force = Mass x Acceleration
  • F = ma
• Newton's Second Law (in words)

  An object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
• Weight


  The force that acts on an object due to gravity and the object's mass
• Quantities weight depends on

  • The object's mass
  • The gravitational field strength at the given position in the field
• Unit for weight


  Newton (N)
• Equipment to measure an object's weight

  A calibrated spring-balance or newton-meter
• Constant speed


  When an object is travelling at a constant speed but not a constant velocity
• When an object is travelling at a constant speed but not a constant velocity
• Circular motion


  • Speed is a scalar quantity
  • Velocity is a vector quantity which means it can only be constant if the direction is constant
  • In circular motion, the direction is continuously changing
  • Velocity is constantly changing
• Centripetal force


  The resultant force that acts on an object moving in a circle, and it acts towards the centre of the circle
• Inertial mass


  • A measure of how difficult it is to change a given object's velocity
  • The ratio of force over acceleration
• Newton's Third Law


  Whenever two objects interact, the forces that they exert on each other are always equal and opposite
• Momentum


  Mass x Velocity
• The unit used for momentum is kgm/s (kilogram metres per seconds)
• In a closed system, the total momentum before and after a collision are equal
• Equation linking change in momentum, force and time


  • Force x Time = Change in Momentum
  • F Δt = mΔv
• Measuring human reaction times

  1. Using the ruler drop test

  2. Person A and B hold each end of a ruler with the 0 cm mark at the bottom

  3. Person A drops the ruler without telling person B

  4. Person B catches it

  5. The distance travelled corresponds to their reaction time
• Importance of 0cm mark at the bottom

  So you can obtain the distance directly without having to calculate it; otherwise, a zero error would need to be accounted for
• Stopping distance


  The sum of thinking distance and braking distance
• If the vehicle's speed is increased


  The stopping distance is increased
• Typical range of values for human reaction time is 0.2 seconds - 0.9 seconds
• Factors which can affect a driver's reaction time

  • Tiredness
  • Drugs
  • Alcohol