Here's the breakdown:
* Longitudinal Wave: In this type of wave, the particles of the medium vibrate *parallel* to the direction the wave travels. Think of a slinky being pushed and pulled back and forth.
* Compression: A compression is the region in a longitudinal wave where the particles are closely spaced together. This is where the medium is most dense.
* Rarefaction: The opposite of a compression is a rarefaction, where the particles are spread out and the medium is less dense.
Think of a sound wave:
* When you hear a sound, it's because a longitudinal wave is traveling through the air.
* The compressions are areas of high pressure (where the air molecules are packed together).
* The rarefactions are areas of low pressure (where the air molecules are spread out).
So, to answer your question directly: A region where matter is more closely spaced in a longitudinal wave is called a compression.
