Question

PLEASE GIVE MORE THAN YES OR NO ANSWERS

a) Does the pitch of the noise made by striking a bottle get higher or lower as you fill the bottle with water?

b) Does the pitch made by blowing across the top of the bottle go up or down as you fill the bottle?

c) Why is there a difference between these two noises? In your answer, comment on the source of the noise in each case (i.e. What is vibrating?).

d) Using what you know about harmonics and resonance, explain how different pitches are created when you blow across the bottle opening with different liquid levels.

e) What wave property allows you to hear noise through a bottle held up to your ear when someone blows across the top of a bottle across the room, and how does the sound transmit from one bottle to the other? Will the pitch sound the same as the one made by the person across the room?

Answer 1

a) The pitch of the noise made by striking a bottle get LOWER When the bottle is empty, the glass can vibrate quickly since the water is not there to push back on the glass, so with no water, you get a high note and viceversa.

b) As I blow across the open top, the air inside the bottle is set into vibration (as the air moves across the top, the pressure of the air above the bottle changes and the air inside the bottle starts to move or vibrate). The more air there is to vibrate, the lower the frequency of the vibration (or pitch). Hence the pitch will go higher.

c) Definitely The pitch is different when you tap it compared to when you blow into it. The difference occurs because you are setting different materials into vibration: The glass vibrates when you tap and the air vibrates when you blow across the opening. When the bottle is empty, the glass can vibrate quickly since the water is not there to push back on the glass, so with no water, you get a high note. When you blow, the greater the air space, the lower the pitch, just the opposite of tapping the glass.

d) When you blow on the edge of the bottle you are making a jet of air, if you hold your fingers nearby you can feel it. If you are making a noise this jet of air could either be deflected into the bottle or over the top of it, and it only takes a small force to change between these two paths.If the air starts off going into the bottle, there is nowhere for it to escape so the pressure builds up, at some point the pressure builds up so much that the jet is pushed out of the bottle. Now the fast moving air sucks air out of the bottle until the pressure is low enough to suck the jet back in. You have made a vibration.