Q1.
Two astronauts are repairing the arm of a space station together during a spacewalk. Can they talk to each other and hear the sounds of metal clanking as they do on the Earth?
Answer
No — not directly. Outer space is a near vacuum, and a sound wave has nothing to travel in there.
Why it happens: sound is a series of compressions and rarefactions — regions where the particles of a medium are pushed closer together and pulled further apart. A particle can only pass the disturbance on by colliding with a neighbouring particle. Where there are almost no particles, there are no collisions, so there is nothing to carry the disturbance. This is exactly what the vacuum bell jar experiment (Fig. 10.7) shows: as the air is pumped out, the bell is still seen ringing but the sound fades to nothing.
On the Earth the same clank is heard easily because the air between the two astronauts is a perfectly good medium.
Did you know? Astronauts talk over radio sets built into their suits. Radio waves are electromagnetic waves, not mechanical waves, so they need no medium and cross the vacuum happily. If two helmets are pressed together, the clank can be heard — the solid helmet material then acts as the medium.