# 20. Motion Concepts - Sonic Ranger

A sonic ranger measures the distance to a moving object by bouncing ultrasonic sound off the object and timing the echoes. The data, taken about every 0.05 sec. is read into a computer which then plots the distance, velocity, and acceleration. The results can appear on overhead projection via the LCD screen, or in some rooms, directly on video projection. Derivatives, integrals and other manipulations of these quantities can be performed. Three typical experiments are described:

 1. A cart is sent up a tilted Pasco track to roll back down. This is a good demonstration to illustrate kinematics concepts since the students can see distance, velocity, and acceleration plotted simultaneously.
 2. A plate is supplied which the instructor can move in various ways to again illustrate d, v, and a. Start simple; hold the plate at constant position for a few moments, move at constant velocity to a new position, and hold this new position for a few moments. Have the students predict the graphs of d,v, and a.
 3. A pendulum is set swinging and the computer plots out the sine and cosine waves of d, v, and a. Their phase relations can be pointed out. Try reassigning the axes to plot d against v.

Several different sonic rangers with their associated software, computers, and projection equipment are presently being tried in the classrooms. Plan on familiarizing yourself a little with the specific equipment before using it in your class.