Waves are everywhere. But what exactly is a wave? A wave is a disturbance. It transfers energy from one place to another. It happens in a regular and organized way. The study of waves is very important in science and engineering. There are different kinds of waves. Some waves must travel through a medium, like air. These are called mechanical waves. Sound waves and water waves are mechanical waves. So are seismic waves. Seismic waves lead to earthquakes. Electromagnetic (EM) waves are another kind of wave. These include light, radio waves and microwaves. They do not require a medium. They can travel through a vacuum. In physics, a vacuum is any space that contains little or no matter. Types Of Waves There are two main categories of waves. One is transverse waves. The other is longitudinal waves. How do we tell them apart? It depends on the direction the wave travels. And it depends how the direction is related to the direction of the wave disturbance. Transverse Waves In a transverse wave, the direction the wave travels is perpendicular to the direction of the disturbance. A water wave is an example. The wave travels in a horizontal direction. It moves across the water surface. The disturbance is vertical. This is the up-and-down motion of the water. A jump rope can show how transverse waves work. One end of the rope is tied to a doorknob. A person holds the other end. The person flicks the rope up and down. This creates a disturbance. Energy from the person's hand sends a wave along the rope. It moves up and down. This movement travels the length of the rope. Note that the wave moves horizontally across along the rope. The disturbance moves up and down. This is what makes it a transverse wave. Image 3.A longitudinal wave travels in the same direction as the disturbance that caused it. Transverse waves can be represented by a curved line passing above and beneath a straight line. A transverse wave travels at a right angle to the direction of disturbance. Image credit: Encyclopædia Britannica, Inc. Longitudinal Waves A longitudinal wave is different. It travels in the same direction as the disturbance. Imagine a Slinky toy. The spring is pulled. Then it is released at one end. The coils closest to this disturbance move forward and bunch up. Then they move backward and spread out. This motion repeats along the length of the spring. The disturbance is the bunched-up areas. It moves in the same direction as the wave. Sound waves are longitudinal waves. Say you strike a tuning fork. The vibrations of the fork disturb the air particles around it. The air particles move forward and backward. The moving air particles, in turn, disturb their neighbor air particles. They disturb their neighbor air particles. This goes on and on. Remember that the air does not travel. The particles of air do not move forward. Instead, the disturbance moves forward. It moves with the wave. .