Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. Sometimes speed and direction are combined as a velocity vector; wave number and direction are combined as a wave vector.
Price of a Stamp. The current price of a first class stamp is 47 cents. A domestic first class letter (1 oz.) is 47 cents. The price of each additional ounce is 21 cents. It will cost you 34 cents to send a domestic postcard.
The price of the popular Forever stamp is about to go up. The U.S. Postal Service (USPS) first announced the change in October, though the change doesn't take effect until Sunday, Jan. 22. At that point it will cost you 49 cents, up from 47 cents, to mail a one-ounce first-class letter.