Why cannot a sound heard on the moon? How do astronauts talk to one another on the surface of moon?

How does sound from a sound producing body travel through air to reach our ears? Illustrate your answer with the help of a labelled diagram.

An electric bell is suspended by thin wires in a glass vessel and set ringing. Describe and explain what happens if the air is gradually pumped out of the glass vessel.

When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its dound cannot be heard through the air. Why?

How could you convince a small child that when you speak, it is not necessary for air to travel from your mouth to the ear of a listener?