Reference Frames

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Contents

  1. Reference Frames
  2. Inertial Reference Frames

Reference Frames

  • A reference frame (or frame of reference) is a system of coordinates, units of measurement, synchronized clocks, and measuring rods, pegged to a particular location, that is used to measure physical phenomena such as position, distance, velocity, and acceleration.
  • For example, using Cartesian coordinates and SI units, a flash of light might occur at (500, 3, 2, 4), that is:
    • at the point 3 meters along the x-axis, 2 meters along the y-axis, and 4 meters along the z-axis
    • at the time 500 seconds after initial time zero.
  • A reference frame can be pictured as a latticework of measuring rods and synchronized clocks.

Inertial Reference Frames

  • An inertial reference frame is a reference frame in which the Law of Inertia is true, that is:
    • A body at rest remains at rest and a body moving in a straight line at constant speed remains moving in that line at that speed, unless acted on by a force.
  • An inertial reference frame doesn’t accelerate or decelerate, rotate or change direction.
  • A pendulum can be used to determine whether a reference frame is inertial. For example, the reference frame of a maglev train traveling at 400 mph.