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# Waves watch

• Can I have an explanation on this phenomena. When we fill half of a glass bottle with water, the sound produced when we hit it lightly ( with a fork of something ) is different compare to a glass bottle which is almost full of water. How can we explain it scientifically with application of frequency ( or something) ?

1. (Original post by TammyChong)
• Can I have an explanation on this phenomena. When we fill half of a glass bottle with water, the sound produced when we hit it lightly ( with a fork of something ) is different compare to a glass bottle which is almost full of water. How can we explain it scientifically with application of frequency ( or something) ?

What's the difference in pitch between the two? What effect did having more water have on the pitch?
2. Having more water will decrease the pitch? But why?
3. More massive -> lower frequency.
(Greater mass = greater inertia so the particles don't vibrate as much!)

As you add more water, mass increases -> less vibration -> resonance frequency decreases -> pitch drops
A thinner (less stiff) glass would also vibrate slower.
4. Thanks, but I have one more question. Is the stiffness in this situation refers to young modulus? I thought the stiffness of a material is the same since it is a property of a material. Then, why does a less stiff glass will vibrate slower? I hope that's not too much questions!

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