Question

Sound travels _____________ times faster in water than in air.

Answer 1

Hint: Sound propagates in a medium through the vibration of the particles of the medium. The periodic vibrations of the particles lead to continuous disturbance in the medium and the sound waves travelling further. Thus, a medium which has a lot of particles in a small volume will aid in sound travelling faster.

Complete step-by-step answer:

Sound is a mechanical wave. This means that it requires the presence of an elastic medium to propagate (unlike light, which is an electromagnetic wave and can propagate even in the absence of a medium).
Sound propagates in a medium through the vibration of the particles of the medium. The periodic vibrations of the particles lead to continuous disturbance in the medium and the sound waves travelling further.
When sound waves pass through a medium a part of the medium gets stretched while the other gets compressed. This leads to a wave-formation and propagation of the sound. Thus, how much the medium can stretch and compress becomes a factor in the speed of propagation of sound. This is why it is said that the speed of sound depends upon the elastic properties of a medium.
The particles of water are much closer together than in air. So, they can easily transmit disturbance by vibrating and passing on the vibrations to the next particle and so on. So, sound travels faster in water than in air.
The speed of sound in water in typical conditions is about $1480m{{s}^{-1}}$.
The speed of sound in air in similar conditions is about $340m{{s}^{-1}}$.

Therefore sound travels about $\dfrac{1480}{340}=4.35$ times faster in water than in air.

Note: Since sound is a mechanical wave it cannot travel through vacuum. So, astronauts on the moon cannot speak to each other normally.
Since, the speed of sound increases if particles are closer together in a medium. The speed of sound in solids is greater than in liquid which is greater than in gases since particles are closer in solids than in liquids than in gases.
This is also the reason why sound travels faster in seawater than in freshwater. Seawater has salt in it which adds more particles to the particles of water in the medium, thus making the overall particles closer.