Forces/motion

• What is the definition of a scalar?

  A scalar has just magnitude.
• What is the definition of a vector?

  A vector has magnitude and direction.
• Can scalars be negative?

  Generally, scalars cannot be negative.
• Can vectors be negative?

  Yes, vectors can be negative as a certain direction is positive.
• What are examples of scalars and vectors?

  • Scalars: Speed, Distance, Time, Mass, Energy
  • Vectors: Velocity, Displacement, Acceleration, Force, Momentum
• What is the displacement of a ball thrown off a cliff at the height of the cliff?

  The displacement is 0 at the height of the cliff.
• How is displacement defined above and below the cliff?

  Above the cliff, the displacement is positive, and below the cliff, it is negative.
• What does speed become when a direction is given?

  Speed becomes velocity when a direction is given.
• What do displacement-time graphs represent?

  • Gradient represents velocity.
  • Sharper gradient means faster speed.
  • Negative gradient indicates returning to the 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 means 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?

  Use overall distances and timings to work out average speed.
• What are the methods to determine speeds?

  • For constant speeds: Measure distance and time, then use speed = distance/time.
  • For average speed: 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, approximately 1.4 m/s.
• What is the typical running speed?

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

  15 km/h, 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?

  • Measured using a force meter or weighing scales.
  • Used to determine the mass of an unknown object.
  • Greater gravitational field strength results in greater weight.
• What is circular motion?

  • Object moving in a circle with constant speed.
  • Speed is constant, but direction is always changing.
  • Velocity is always changing, hence it is accelerating.
• What is centripetal force?

  • The force required for circular motion.
  • It supplies the acceleration 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 are examples of Newton's Third Law in action?

  • A book on a table: weight of the book equals the reaction force from the table.
  • Rocket taking off: force of gases equals the force lifting the rocket.
  • Collisions: forces exerted by colliding objects are equal and opposite.
• What is human reaction time?

  • Delay between observing an event and acting.
  • Average human reaction time is approximately 0.25 seconds (250 milliseconds).
• How is human reaction time measured using the ruler drop experiment?

  • A ruler is held above an open hand and dropped randomly.
  • Measure the distance caught; average this distance to determine reaction time.
  • 1 cm corresponds to 50 ms, 2 cm to 60 ms, etc.
• What is the average human reaction time?

  Approximately 0.25 seconds (250 milliseconds).