Describe the concept of mechanical waves.

A tuning fork is struck and held above a vertical tube partially filled with water. The water level is slowly lowered until a loud sound is heard at a depth of 18.5 cm below the opening. When the water is lowered further, the next loud sound occurs at 55.5 cm below the opening. Describe the concept of mechanical waves that explains both the requirement for the tuning fork to vibrate and the pattern of loud sounds at specific water levels.

A geologist uses seismic waves to investigate underground rock structures. After an earthquake, two distinct sets of waves are detected by monitoring stations. The first set travels at 6,200 m s⁻¹ through the solid rock and causes particle motion parallel to the direction of wave propagation. The second set travels at 3,400 m s⁻¹ and causes particle motion perpendicular to the direction of propagation. Both wave types require the rock medium to transfer energy. Refer to the scenario above. Describe the concept of mechanical waves using evidence from the seismic wave observations.

A geologist uses seismic sensors to monitor underground vibrations caused by a controlled explosion at a mining site. Data from three sensors at different depths show distinct arrival times and amplitudes for two types of disturbances travelling through the rock and soil layers. Describe the concept of mechanical waves and explain how this concept applies to the disturbances recorded by the sensors.