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.
Mr. Carr is not entirely correct. The USPS issued a global forever stamp that pays the first class postage for an ordinary letter weighing not more than one ounce to anywhere in the world. This stamp was introduced in 2013 and sold for $1.10, the rate current at that time. Now this stamp will cost you $1.15, but if you buy them now, when the rate increases, they will still be valid for the full postage rate at the time. Albert van Veen, Collector and history hobbyist for 50 years.