Motion 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.
• Why can scalars generally not be negative?

  Scalars represent quantities that do not have direction, so they are typically non-negative.
• What is an example of a scalar quantity?

  Speed is a scalar.
• What is an example of a vector quantity?

  Velocity is a vector.
• What is the relationship between distance and displacement?

  Distance is a scalar, while displacement is a vector.

  
• What is the definition of acceleration?

  Acceleration is a vector quantity.
• What is the definition of force?

  Force is a vector quantity.
• What is the definition of mass?

  Mass is a scalar quantity.
• What is the definition of momentum?

  Momentum is a vector quantity.
• What is the definition of energy?

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

  The displacement is 0 at the height of the cliff, positive above it, and negative below it.
• How can you set the "0" point of a vector in long answer questions?

  You can decide where the "0" point lies, such as setting it at the bottom of the cliff.
• What distinguishes speed from velocity?

  Speed is only velocity when given a direction.

  
• What do displacement-time graphs represent?

  • Gradient represents velocity
  • Sharper gradient indicates faster speed
  • Negative gradient indicates returning to starting point
  • Horizontal line indicates stationary
  • 0 distance means back to starting point
  • Area under the line equals nothing
  • Curved line indicates changing velocity (acceleration)

  
• What do velocity-time graphs represent?

  • Gradient represents acceleration
  • Sharper gradient indicates greater acceleration
  • Negative gradient indicates deceleration
  • Horizontal line indicates constant speed
  • 0 velocity means stationary
  • Area under the line equals distance travelled
  • Curved line indicates changing acceleration

  
• How do you calculate average speed when speed changes during motion?

  You use overall distances and timings to work out average speed.

  
• What are the methods to determine speeds?

  • For constant speeds:
  • Measure distance travelled
  • Use stopwatch for time taken
  • Use speed = distance/time
  • For average speed:
  • Work out total distance travelled
  • Find total time taken
  • Use speed = distance/time
  • Using light gates:
  • Set up two gates, measure distance
  • Measure time taken to pass between gates
  • Use speed = distance/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, which is approximately 1.4 m/s.
• What is the typical running speed?

  Approximately 6 miles per hour, which is about 3 m/s.
• What is the typical cycling speed?

  15 km/h, which is approximately 4 m/s.
• What is the typical speed of a bus?

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

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

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

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

  • An object has a constant velocity unless acted on by a resultant force.
  • If a resultant force acts, the object will accelerate.
  • If the resultant force is zero, the object moves at constant velocity or is at rest.
• What is Newton's Second Law formula?

  Force = mass × acceleration, or $F =$$ma$.
• How is weight measured?

  Weight is measured using a force meter or weighing scales.
• What is circular motion?

  • Object moving in a circle with constant speed.
  • Speed is constant, but direction is always changing.
  • Velocity is always changing, so it is accelerating.
  • Requires a centripetal force directed towards the center of the circle.
• What is inertial mass?

  Inertial mass measures how difficult it is to change the velocity of an object.
• What does Newton's Third Law state?

  Every action force has an equal and opposite reaction force.
• What is momentum?

  • Momentum is conserved in a collision without external forces.
  • Momentum formula: $p =$$mv$, where $p$ is momentum, $m$ is mass, and $v$ is velocity.
  • Total momentum before collision equals total momentum after collision.
• How is force related to momentum according to Newton's Second Law?

  Force equals the change in momentum over time: $F =$$\frac{\Delta p}{t}$.
• What is human reaction time?

  • Delay between observing an event and acting.
  • Average human reaction time is approximately 0.25 seconds (250 milliseconds).
  • Ruler drop experiment can measure reaction time.
• What are the components of vehicle stopping distances?

  • Thinking Distance: distance travelled during reaction time.
  • Braking Distance: distance travelled while slowing down to stop.
  • Factors affecting thinking distance: speed, concentration, tiredness, distractions, drugs/alcohol.
  • Factors affecting braking distance: speed, road conditions, tire condition, mass.

  
• How does speed affect braking distance?

  The greater the speed, the greater the distance travelled during the same reaction time.

  
• What are the dangers of large decelerations?

  • Large deceleration in a crash exerts great force on the car and passengers.
  • Force is calculated using $F =$$ma$.
  • High speed before a crash results in high momentum, leading to greater forces felt during a crash.
• How is work done to stop a vehicle related to kinetic energy?

  The work done to stop a vehicle equals the initial kinetic energy of the vehicle.