Q1.
Now, place your ear against the desk, close your other ear and listen again, as shown in Fig. 10.5. Are you able to hear the sound through the table?
Answer
Yes — and the knock or scratch sounds distinctly louder and sharper through the desk than it did through the air.
Why it happens: the knock sets the wood of the desk vibrating. Because the particles of a solid are closely packed and tightly bound, each particle passes the disturbance to the next almost at once and very little energy leaks sideways. Through air the same energy spreads out in all directions and thins out rapidly. So the desk delivers a much larger share of the original energy to your ear.
The conclusion: sound can propagate through solids. Closing the other ear matters — it shuts out the weaker airborne sound so that you are judging only the sound that came through the desk.
Did you know? Sound travels roughly 15 – 20 times faster in solids than in air. This is why a railway track carries the sound of an approaching train long before you hear it through the air, and why Question 11 on page 198 finds a delay of nearly 0.93 s between the two paths along a 340 m steel fence.