Topic 2 – 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 a direction, so they are typically non-negative.
• What are examples of scalars and vectors?

  • Scalars: Speed, Distance, Time, Mass, Energy
  • Vectors: Velocity, Displacement, Acceleration, Force, Momentum
• In the context of a ball thrown off a cliff, what does a positive displacement indicate?

  A positive displacement indicates the ball is above the height of the cliff.
• How can you define the "0" point of a vector in long answer questions?

  You can set the "0" point to be any reference point, such as the bottom of the cliff.
• What distinguishes speed from velocity?

  Speed is a scalar quantity, while velocity includes direction and is a vector quantity.

  
• What do displacement-time graphs represent?

  • Gradient represents velocity.
  • Sharper gradient indicates faster speed.
  • Negative gradient indicates returning to the starting point.
  • Horizontal line indicates stationary.
  • Area under the line represents 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.
  • Area under the line represents 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 calculate average speed.

  
• What are the methods to determine speeds?

  • For constant speeds: Measure distance and time, then use speed = distance/time.
  • For average speed: Calculate total distance and total time, then use speed = distance/time.
  • Using light gates: Measure distance between gates and time taken to pass through.

  
• 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 in physics?

  • An object moving in a circle with constant speed.
  • Speed is constant, but direction is always changing.
  • Velocity is always changing, so the object is accelerating.

  
• What is centripetal force?

  Centripetal force is the force that supplies the acceleration for circular motion, 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.