Sound
Sound waves can travel through solids, liquids, and gases. The thicker the medium, the faster it goes, but they cannot travel through a vacuum (a place with nothing in it). This is why astronauts cannot talk to each other in space: they need a radio to hear each other. Sound can travel through water faster than through air; and even faster in solids like stone, iron, and steel. At room temperature and normal atmospheric pressure, sound travels at 344 m/s (1134 ft/s), 761 miles per hour). Because the temperature and pressure change with altitude in the atmosphere, speed will vary as well.