Section Summary

  • A description of motion depends on the reference frame from which it is described.
  • The distance an object moves is the length of the path along which it moves.
  • Displacement is the difference in the initial and final positions of an object.
  • Average speed is a scalar quantity that describes distance traveled divided by the time during which the motion occurs.
  • Velocity is a vector quantity that describes the speed and direction of an object.
  • Average velocity is displacement over the time period during which the displacement occurs. If the velocity is constant, then average velocity and instantaneous velocity are the same.
  • Graphs can be used to analyze motion.
  • The slope of a position vs. time graph is the velocity.
  • For a straight line graph of position, the slope is the average velocity.
  • To obtain the instantaneous velocity at a given moment for a curved graph, find the tangent line at that point and take its slope.
  • The slope of a velocity vs. time graph is the acceleration.
  • The area under a velocity vs. time curve is the displacement.
  • Average velocity can be found in a velocity vs. time graph by taking the weighted average of all the velocities.