Date: Sat, 26 Feb 2005 20:08:52 -0500 (EST)
Subject: Motion Detector P.O.D.s (mo-PODs)

Q. What is "ultrasound?"
A. "Beyond" sound, that is, sound that is beyond the normal range of human 
hearing (20-20,000 Hz).

Q. How does the motion detector use ultrasound to determine the distance 
to an object?
A1. emit/receive. 1/2 travel time x speed of sound
A2. We know the speed of sound (~343 m/s or ~750 miles/hour). Distance to
target = travel time (TT), to & from target (s) * 343 m/s / 2

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HONORS
Q. If the speed of sound is 343 m/s, then what is the travel time to a
target 3 m from the motion detector?

A. 3m = TTs * 343m/s / 2
3m * 2 = TTs * 343m/s
3m * 2 / 343m/s = TTs
TTs = 0.017 or 0.02 sec

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Q. Refer to the following graph (showing acceleration):
Distance-Match-2_modified_ver2.xmbl
What is the _average speed_ for the 10-sec. time period shown by the 
graph?
A. 0.2 m/sec, ~equal to mid-point of graph.

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Google Search: "speed of sound"

StudyWorks! Online
the Physics Classroom
Lesson 2: Sound Properties and Their Perception
The Speed of Sound
http://www.physicsclassroom.com/Class/sound/u11l2c.html

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Speed of Light = 300,000,000 m/s [300,000 km/s]
Lightning Flash-to-Bang: 1 mile per 5 seconds

http://www.fcps.k12.va.us/fts/safety-security/factsheets/seh-20a.pdf
GUIDELINES FOR LIGHTNING SAFETY DURING ATHLETIC
EVENTS AND ON SCHOOL PLAYGROUNDS
Office of Safety and Security Fact Sheet

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