Singing Wine Glasses

You may think to make music you just need to drag your finger around the top of a glass filled with water. If you drag just your finger across the glass without cleaning or wetting it, there is too much friction created to have the system (the water and the glass) being to oscillate and no sound could be made.

After you wet your finger, wipe off the oils and dirt, and wet it again, the friction is reduced just enough to allow for a stick-and-slip movement. This gives the correct amount of friction to resonate the glass and achieve resonant frequency. The motion of your hand sets up a wave of vibration traveling through the glass that causes air molecules to vibrate at the same frequency causing sound in the air that is picked up by your ear.

The pitch of the sound can be changed by adding or removing water. This is because as the energy wave moves around the glass, it drags the water molecules with it, creating a wave of water that you can see near the edge of the glass. The water molecules increase the mass (amount of water) of the oscillating system and reduce the energy of the wave traveling through the glass (since it is being absorbed by the water) in turn creating a lower frequency.

Key Terms

• Resonant Frequency – the natural frequency at which an object vibrates
• Resonate – forced vibration
• Frequency – how many sound waves are recorded in a given time at a specific point; related to the pitch of a sound
• Pitch – the distinct tone of a sound; the note of a sound
• Friction – the force of two objects rubbing against one another
• Stick-Slip Motion – when an object is able to stick to an object (or medium) for a short time and then slide once again with no change in the amount of force applied
• Oscillation – a consistent repetitive movement, usually seem as either back and forth (vibration) or up and down
• Oscillating System – a system that goes in a consistent repetitive movement; in this case vibrating

Supplies

- Glass with a Stem and Flat Bottom (Wine Glass)

- Water

- Small Towel OR Paper Towel

- Food Coloring* (Optional)

Step 1: Fill the Glass With As Much or As Little Water As You Would Like. Add Food Coloring If Desired.

Step 2: Dip Your Finger Into the Water and Wipe It on the Towel/paper Towel to Remove Any Excess Oil or Dirt.

Step 3: Time to Make It Sing!

To make the glass sing, dip your finger in water and hold the bottom of the glass with your other hand. Start by lightly pressing and going slowly around the rim of the glass. Be sure to keep your finger in constant contact with the rim of the glass. You will have to experiment with the pressure, speed, and where you touch the rim. Note: Some glasses may only give a slight sound and this will NOT work with plastics or thick glassware.

Step 4: Further Exploration

Physics Girl – How I broke a wine glass with my VOICE

(using Science!)

https://www.youtube.com/watch?v=Oc27GxSD_bI

The Sci Guys – Physics of Sound Part 1: Singing Wine Glasses

https://www.youtube.com/watch?v=VN3K9WhzOSs

Glass Duo - Musical Glasses – Harry Potter Theme – LIVE

https://www.youtube.com/watch?v=7hOar8dXNbA

roberttiso – Fur Elise on glass harp

https://www.youtube.com/watch?v=47TGXJoVhQ8

GlassDuo – Glass Harp – Sugar Plum Fairy by Tchaikovskly

https://www.youtube.com/watch?v=QdoTdG_VNV4