Humans have two kidneys and each kidney is supplied with blood from the renal artery. The kidneys remove from the blood the nitrogenous wastes such as urea, as well as salts and excess water, and excrete them in the form of urine.This is done with the help of millions of nephrons present in the kidney.umans have two kidneys and each kidney is supplied with blood from the renal artery. The kidneys remove from the blood the nitrogenous wastes such as urea, as well as salts and excess water, and excrete them in the form of urine.
This is because the speed of sound waves depends upon the material through which they are travelling. Sound travels 15 times faster through the metal railway tracks than through air, giving the cowboy an early warning of the train's arrival. How much plainer could it be? I, personally, had never thought of it that way. I love this illustration.
1 How fast sound travels (i.e. the speed of sound) depends on what medium it is traveling through. 2  The speed of sound is 340 meters per second in air while as the speed of sound is 1450 meters per second in water.e hear sounds because the vibrations created travel through the air to our ears. Notice that when people want to hear something better they often cup their hand around their ear. This is to help them catch the sound waves.