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Section Summary

Section Summary

2.1 Relative Motion, Distance, and Displacement

  • 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.

2.2 Speed and Velocity

  • 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.

2.3 Position vs. Time Graphs

  • 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.

2.4 Velocity vs. Time Graphs

  • 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.