Topic 2-Motions and Forces

• What is the definition of a vector?

  A vector has magnitude and direction
• What is the definition of a scalar?

  A scalar has just magnitude
• Can scalars be negative?

  No, scalars cannot be negative
• What is the scalar quantity for distance?

  Distance is a scalar
• What is the vector quantity for displacement?

  Displacement is a vector
• What is the scalar quantity for time?

  Time is a scalar
• What is the vector quantity for acceleration?

  Acceleration is a vector
• What is the vector quantity for force?

  Force is a vector
• What is the scalar quantity for mass?

  Mass is a scalar
• What is the vector quantity for momentum?

  Momentum is a vector
• What is the scalar quantity for energy?

  Energy is a scalar
• How does displacement change when a ball is thrown off a cliff?

  • Displacement is 0 at cliff height
  • Positive displacement above the cliff
  • Negative displacement below the cliff
• What is the significance of the "0" point in vector questions?

  You can set the "0" point arbitrarily
• What makes speed a scalar and velocity a vector?

  Speed lacks direction, velocity includes direction
• What do displacement-time graphs represent?

  • Gradient represents velocity
  • Sharper gradient means faster speed
  • Horizontal line indicates stationary
  • Curved line indicates changing velocity

  
• What do velocity-time graphs represent?

  • Gradient represents acceleration
  • Sharper gradient means greater acceleration
  • Horizontal line indicates constant speed
  • Curved line indicates changing acceleration

  
• What is the formula for average speed?

  Average speed = distance / time
• What are methods to determine speeds?

  • Measure distance and time for constant speed
  • Use light gates for accuracy
  • Calculate average speed from total distance and time
• What is the typical speed of wind?

  5 − 7 m/s
• What is the typical speed of sound?

  340 m/s
• What is the typical walking speed?

  5 km/h = ~1.4 m/s
• What is the typical running speed?

  ~6 miles per hour = ~3 m/s
• What is the typical cycling speed?

  15 km/h = ~4 m/s
• What is the typical bus speed?

  14 km/h
• What is the typical train speed?

  125 miles/h
• What is the typical plane speed?

  900 km/h
• What is the acceleration due to gravity?

  $g =$$10 \, \text{m/s}^2$
• What does Newton's First Law state?

  • Constant velocity unless acted on by a resultant force
  • Acceleration occurs with resultant force
  • Zero resultant force means constant velocity or rest
• What is Newton's Second Law formula?

  Force = mass × acceleration
• What units are used for force, mass, and acceleration?

  Force in Newtons, mass in kg, acceleration in m/s²
• How is weight measured?

  • Using a force meter or weighing scales
  • Greater gravitational field strength means greater weight
• What is circular motion?

  • Constant speed but changing direction
  • Velocity is always changing
  • Requires centripetal force directed towards the center
• What is inertial mass?

  Measure of difficulty to change velocity
• What does Newton's Third Law state?

  Every action has an equal and opposite reaction
• How does momentum behave in collisions?

  • Momentum is conserved in collisions
  • Total momentum before equals total momentum after
  • Momentum is a vector quantity
• What is the formula for momentum?

  Momentum = mass × velocity
• What is the unit for momentum?

  kg·m/s
• What is the formula for force in terms of momentum?

  Force = change in momentum / time
• What is human reaction time?

  • Delay between observing and acting
  • Average human reaction is 0.25 seconds
  • Ruler drop experiment measures reaction time
• What are vehicle stopping distances?

  • Distance traveled during reaction time (thinking distance)
  • Distance traveled while braking (braking distance)