What is the meaning of longitutinal wave?

Answer 1

Picture two people holding holding opposite ends of a long spring that they've stretched between them. If you're familiar with the toy called a "slinky", that's what I'm talking about. Now imagine that a small portion of the slinky in the middle is painted bright orange. If one person shakes his end of the slinky up and down, a wave will propagate toward the other person. If you were to observe the orange part of the slinky, you'd see that it moves up and down with the motion of the wave. This type of motion, where the orange section moves perpendicular to length of the slinky, is called transverse motion. Hence, this is a transverse wave.

A longitudinal wave is different; it's a wave where the particle motion is parallel, rather than perpendicular, to the length. Imagine the same two people holding the same slinky with the bright orange section in the middle. Now imagine that one of the people quickly pushes his end of the slinky toward the other person, then pulls it back (as if he was imitating the motion of passing a Basketball to his friend). The motion would cause the slinky to compress slightly near the first guy. The compression wave would then travel through the spring toward the person at the other end. If you were to observe the bright orange section in the middle, you'd see that the wave motion would cause it to move back and forth along the length parallel to the length of the slinky. That's a longitudinal wave.