The behavior of a sound wave is affected by the density of the medium, the temperature of the medium and the pressure of the medium if it is a gas. Motion of the medium independent of the sound wave may also affect the way sound propagates.
Yes, you may check-in for your Delta Air Lines (DL) flight with your mobile device starting 24 hours and ending 60 minutes before the scheduled departure time (depending on your departure city and destination) to receive a mobile boarding pass on your mobile device.
How to check in your bags for free on Delta, Continental. Published 5:30 am, Monday, May 17, 2010. Delta has a new baggage offer that could help ease the onboard roller derby for overhead space. Beginning June 1, Delta American Express affinity cardholders will be able to check one bag free on Delta. Delta currently charges $25 each way to check a bag, so you could save $50 each time you fly round trip if you have the card. The offer extends to up to nine people flying on the same reservation, so if you have a family of four, you could save $200 round trip if each person checks one bag. Even with this offer, you'll want to pack light; Delta charges $35 each way for the second bag. The annual fee for the cards starts at $95, but those fees could easily be made up if you fly several times a year or if you travel with family.