- Feb 4, 2006
 
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Based on your post, I shall be trying this at the weekend with my son.
If you can choose an open area with a hard surface or a body of still water so the sound isn't impeded as it travels from your son to you. I think you will need at least two full blocks distance between you and him. A good test would be to make a loud sharp sound rather than voice. You can easily see a hammer striking a frying pan better than mouth movements, but the resulting delay would be the same.
Speed of sound = 1200 ft/sec
Speed of light = 186,000 mile/sec
A sound made 1200 feet (four football fields away) from you takes a full second to reach you while the image of the source of that sound reaches you instantly.
			
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