Motion Summary

SI Units

  • Agreed units of measurement for worldwide use.
  • Combinations of these units can be used to produce SI units for all other quantities. For example, the SI unit for speed is m/s.

Distance vs Displacement

  • Distance: Total ground covered; scalar quantity (magnitude only).
  • Displacement: How far the start and end points are from each other; vector quantity (magnitude and direction).

Scalars and Vectors

  • Scalar: Magnitude only (e.g., length, area, volume, speed, mass).
  • Vector: Magnitude and direction (e.g., displacement, velocity, acceleration, force).

Speed

  • Measure of how quickly something moves; scalar quantity.
  • Units can vary (e.g., km/h, m/s).
  • Average speed : v = \frac{d}{t}

Velocity

  • Measure of how much displacement changes with time; vector quantity.
  • Measured in m/s.

Average vs. Instantaneous Speed

  • Average speed: Total distance over total time.
  • Instantaneous speed: Speed at a particular point in time.

Conversions

  • Use the value 3.6 only for km/h to m/s

Sonar

  • Sound Navigation and Ranging.
  • Used to map ocean floors by measuring the time it takes for a signal to return.

Acceleration

  • Rate of change in velocity; vector quantity.
  • Measured in m/s². Textbook error.
  • Three ways to change:
    • Speed up.
    • Slow down.
    • Change direction.

Constant Velocity vs. Constant Acceleration

  • Constant velocity: No acceleration.
  • Constant acceleration: Constant change in velocity.
  • a = \frac{v-u}{t}, v = u + at

Falling Objects

  • Accelerate at 9.8 m/s² due to gravity.
  • Terminal velocity: Maximum velocity reached due to wind resistance.

Motion Graphs

  • Types:
    • Displacement vs. time (x-t).
    • Velocity vs. time (v-t).
    • Acceleration vs. time (a-t).
  • Gradient and area under the graph provide useful information.

Displacement vs. Time Graphs (x-t)

  • Shows position change relative to the starting point.
  • Gradient = average velocity.

Velocity vs. Time Graphs (v-t)

  • Point on graph = velocity at a certain time.
  • Gradient = acceleration.

Summary of Motion Graphs

  • x-t: Gradient = velocity, Point = displacement
  • v-t: Gradient = Acceleration, Point = velocity
  • a-t: Point = acceleration