Question

what defines a longitudinal wave?
particles of the
medium do not mov
from their position.
particles of the
medium move in a
circular motion.
particles vibrate
perpendicular to the
direction of the waves
motion.
particles vibrate
parallel to the
direction of the waves
motion.

Explanation:

In a longitudinal wave, the particles of the medium vibrate parallel to the direction of the wave's motion. This is a key characteristic that distinguishes longitudinal waves from other types like transverse waves (where particles vibrate perpendicular to the wave's direction). The other options are incorrect: particles in a medium do move (so the first option is wrong), circular motion of particles is not a defining feature of longitudinal waves (second option wrong), and perpendicular vibration defines transverse waves (third option wrong).

Answer:

Particles vibrate parallel to the direction of the wave's motion.