Sound Waves:
Sound waves are a broadcast of sound through a medium (the substance sound travels through i.e. air, water, gas, etc.). In our experiment, we had two mediums, water, and air. The air medium was our control, and our experiment took place using a water medium. Sound waves travel through different mediums in a “wave-like” shape, hence the name “sound wave”. Diagrams by Johnny

To actually produce a sound, the particles in the medium (water particles, air particles, gas particles, etc.) vibrate according to the direction the sound waves are moving. When a sound wave comes into contact with a medium particle, it disturbs it from its resting position, which in turn disturbs all of the other medium particles from their resting position. The movement of several particles near each other creates a region of space where medium particles are compressed together, creating a compression area or high-pressure area. After the sound wave has passed, a restoring energy usually pulls the medium particles back into their original position, creating a space where the particles are spread apart called a low-pressure area or a rarefaction. Compression areas and rarefactions are known as pressure waves.
Hearing:
Hearing is enabled when pressure waves reach the eardrum inside the human ear. When a compression wave reaches the ear, the eardrum is pushed inwards. When a rarefaction wave reaches the ear it pulls the eardrum outwards. The constant “in and out” motion of the eardrum causes vibrations. The eardrum is attached to the bones of the middle ear (hammer, anvil, and stirrup) that start vibrating when pressure waves are received by the eardrum. The vibrations are the transmitted to the fluid of the inner ear. The vibrations are converted to electrical nerve impulses that are sent to the brain. Higher frequency sound waves are heard as higher pitched sounds by the human ear, and lower frequency sound waves are perceived as lower pitched sounds.