Which one of the following statements is NOT true about the sound waves?

CONCEPT:

Mechanical waves:

• The oscillation of matter which is responsible for the transfer of energy through a medium is called a mechanical wave.
• The mechanical wave always needs a medium to travel.
• It can’t travel through a vacuum.
• The wave which propagates in a solid, liquid, or gaseous medium is called an elastic wave.

There are two types of mechanical waves:

Transverse waves:

• The wave in which the movement of the particles is at right angles to the motion of the energy is called a transverse wave.
• Light is an example of a transverse wave.

Longitudinal wave:

• The wave in which the movement of the particles is parallel to the motion of the energy is called a longitudinal wave.
• A sound wave is an example of a longitudinal wave.

EXPLANATION:

• Sound waves need a medium to travel. Hence, it can propagate through the water. 
• The speed of sound waves in steel is more than its speed in the air since the molecules in solid material are closely packed together and can transfer the energy faster than molecules in liquid which are loosely packed.
• A sound wave is an example of an elastic wave and longitudinal wave and due to the elastic wave nature of the sound wave, it can’t travel in a vacuum.