How and why do we hear through the brick walls? Does the sound actually penetrate the walls?
Have you done any research? What have you found?
Sound is a vibration. The vibration causes other things to vibrate. If I pluck a guitar string, causing the string to vibrate, it causes the air to vibrate, and that vibration eventually reaches your ear, where you hear it because the vibrating air causes your ear drum to vibrate. You hear a sound whenever anything causes air to vibrate that can reach your ear drum, provided it's loud enough and within the frequency range that your ear is designed for.
If I tap on a brick wall, can you hear it? Yes. That tells you that vibrations travel through brick. And you hear it, because again the vibration of the brick causes vibration in the air which vibrates your ear drum.
There are a lot of properties that all waves have in common. One of them is what happens at an interface between two types of medium, for instance going from air to brick. The wave can reflect, or it can be transmitted forward into the new medium. Usually a combination of both. And once in a medium, the wave might travel with very little loss of energy (like light through glass) or it might gradually lose energy as it travels (like light through a murky liquid).
All of that happens with sound. Hard materials like brick tend to reflect a lot, but some energy is transmitted into the brick. But sound within hard materials tends to travel very fast without much loss of energy, so any sound that does penetrate the brick will get readily to the other side.
Edit to add: Another property that sound shares with other waves is diffracting around barriers. So if you are talking about a brick wall outside, with air above, some of the sound can readily bend around the top of the wall and reach you through the air that way.
Yes, sound can penetrate brick walls. Sound is what our ears hear due to pressure from the vibration of air molecules. The pressure from the vibration of air molecules on one side of a wall can also vibrate brick molecules. As the vibrations carry through the brick wall, they will vibrate the air molecules on the other side of the wall. These vibrations will be picked up by your ears as the sound that was generated on the other side of the wall.
A fun note is that this concept has been used to monitor sounds inside a room from outside that room by observing the vibrations of the room’s glass window.
Apparently, this plays a large part in sound leakage. Simply stuffing air gaps between rooms (such as electrical outlet boxes that often bridge wall spaces) has a big effect on reducing sound leakage.
The sound that gets through small holes between rooms is particularly annoying because it tends to consist of only the highest frequencies so you just hear a tinny sounds and the squeaky parts of kids voices - from one classroom into the staff room in school!!!!!
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