Robert Benavidis age 10, of Chicago, Ill ; for  his question:

Is the speed of sound. always the same?

Sound is sometimes in a great hurry and sometimes it just dawdles along. However, even at its slowest, it is faster than you can run. It dawdles through the air, But an airplane must break the sound barrier to reach the speed of sound. Pilots call this the speed of Mach I. Near the surface of the ground, Mnch I is estimated to be 750 miles per hour. But Mach I varies with the height of the plane and the temperature of the day, This is because sound does not always travel at the same speed.

As the temperature rises, sound travels faster. It slows up as the temperature drops, The higher we go in the air, the cooler it gets. This means that sound travels more slowly high above the ground, A high flying plane does not have to travel quite so fast to break the sound barrier, A low flying plane over a scorching desert must fly faster to reach the speed of sound.

Sound speeds up at a regular rate with the temperature. At freezing point, it whips along through the air at about 1,087 feet a second, This is about one mile in five seconds. At one centigrade degree above freezing, sound increases its speed by two feet a second, It adds two feet to every second of travel time as the temperature rises one centigrade degree. At 20 degrees centigrade, which is room temperature, sound whips through the air at about 1,127 feet a second.

In order to travel at all, sound must always pass through something. It can travel through air, which is made of gases, through liquids and through solids. All these things are made of tiny atoms and molecules. In the gases of the air, these particles are spread apart with plenty of space between them.

In liquids and solids, they are more closely packed together. Solids are made of dense materials. Liquids are not so dense as solids, but they are far more dense than the gases of the air.

Now we can travel much faster through the air than through the water. It would take us even longer, much longer, to dig our way through the solid. ground and we probably could not travel through a steel bar at all, With sound, just the opposite is true. It is slowest when traveling through the air faster when traveling through water and fastest when traveling through heavy metals. The more dense the object, the faster sound can travel through it,

This is because sound depends upon the tiny particles, the atoms and molecules from which a substance is made. They hand the sound along on  its journey from one to another. The closer they are, the faster the sound can travel, Through water sound travels at about one mile a second, five times faster than through the air. Through dense steel it travels three miles in a second, If the temperature of the water or steel becomes higher, the sound travels even faster.