## 2 Quick questions on Sound and echoes

Q1. What makes a medium a good transmitter, reflector and absorber of sound?
I understand that for a medium to be a good transmitter (ie sound travels fast through it), the medium must be elastic. Think of golf balls connected by springs. The springs are very elastic and stiff, hence any disturbance through the medium moves fast.

For a medium to be a good absorber, i think it has to be the opposite of being elastic. Preferably the medium is soft and contains trapped pockets of air, like styrofoam or fur.

For a medium to be a good reflector, i think the medium has to be hard and dense. Which begs the question: "Is a good sound transmitter also a good sound reflector?" (i.e. what is the difference between a good transmitter and reflector?)

Can forummers help to evaluate my thoughts above, as well as to answer the last question i asked? Thanks

Q2. Should we use the "Law of Reflection" to determine if echoes can reach us after bouncing off buildings?"

Do "sound ray" follow the same behaviour in the same way that "light rays" do? We often use the geometry of incident and reflected angles to determine if light can reach our eyes. Should we also adopt the same approach to ascertain if echoes from a source can reach our ears?

I am asking this because i am stumped by a question, which has a boy standing in front of two buildings - the taller one is behind the shorter one. The boy is facing the shorter building. The question asked what will the boy hear instants after letting out a shout. I analyze the diagram, and realise that there is no way the reflected sound can reach the boy after bouncing off from the taller building behind. I am hence tempted to say that the boy can only hear one echo, coming from the shorter building in front of him. (i am assuming specular reflection off smooth surfaces.)

Can forummers shed light on this issue please?

Thanks.

From a high school Physics teacher.

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