Learning standards covered by this activity:

Major Understanding

• 4.3f Resonance occurs when energy is transferred to a system at its natural frequency.
• 4.3m When waves of a similar nature meet, the resulting interference may be explained using the principle of superposition. Standing waves are a special case of interference.

Process Skill

• 4.3 iii. identify nodes and antinodes in standing waves
• 4.3 vi Predict the superposition of two waves interfering constructively and destructively (indicating nodes, antinodes, and standing waves)

The above learning standards were taken from the Core Curriculum Physical Setting/Physics, The University of the State of New York, The State Education Department.

Wine Glass Resonance Materials

• wine glass, the thinner the rim of the glass the better
• water
• soap

Procedure

1. Wash your hands with soapy water for best effect.
2. Fill the glass part of the way with water
3. Dip the tip of your finger into the water then slowly and lightly rub the rim of the glass with your moist finger
4. After a few seconds the glass will start to sing
5. You can change the pitch of the note by adding or subtracting water

Singing Rod Materials

• Rosin (from the music room)
• Metal rod from your ring stands (or any other uniform metal rod will do)

Procedure

1. Crush a pea sized amount of rosin on a piece of paper until it is ground into power.
2. Cover the tips of your thumb, index and middle finger of your non-dominate hand with rosin as if you were going to use the rosin to make a finger print.
3. With your other hand grasp the metal rod with your thumb and index finger exactly in the middle of the rod.
4. Stroke one half of the rod with your rosin covered fingers. After four or five strokes a standing wave will build up as the other end of the rod begins to resonate.

Explanation
Every object has a natural frequency. If you drop a set of car keys it makes a recognizable sound, as does dropping a pin. The sound that it makes is the natural frequency of the keys and the pin. You can get the rim of the glass to vibrate at the natural frequency of the glass by rubbing the rim with your finger. Your fingertips cause the glass to vibrate at it’s natural frequency. If this happens over and over again a standing wave builds up and you can get a sound with a lot of volume.

If you cause an object to vibrate at its natural frequency by having another object near vibrating at the same frequency you can set up a standing wave in the first object. This process is called resonance. This is what is happening with the singing rod. Since you are holding the rod at its middle point, the natural frequency of both ends of the rod is the same. As you set up a standing wave with your hand on one end of the rod, there is a standing wave set up due to resonance on the other end of the rod. Be careful, you can get the rod to sing loud enough to be painful to some people’s ears.

Reinforcement Activities
Look on the internet for small video clips of the Tacoma Narrows Bridge Collapse or Galloping Gurdie. Both of these names reference a bridge that collapsed due to resonance. The wind blew across the bridge at the same frequency as the natural frequency of the bridge. The standing wave produced was a couple of meters high and eventually the bridge shook so violently it collapsed. A great video for getting your students thinking and talking about standing waves and resonance.

Myth Busters did an interesting video on resonance trying to shatter a wine glass with their voice. Other Myth Busters videos are available for purchase through Cenco Physics. (See the related products section below.)

Allow students to play with resonance on their own using the differential and sympathetic Tuning fork set. Have students set up a wave on one tuning fork and then match the same frequency with a second tuning fork. When the tuning forks are matched in natural frequency then second fork will ring without being struck.

Related Products

• Standing wave demonstrator - an economical way to create large standing waves.
• Spiral Spring - classroom size.
• String vibrator - Teach students about wavelength, modes of vibration and frequency with this inexpensive, easy-to-use apparatus.
• “Slinky” springs - Superb for illustrating both transverse and longitudinal waves.
• Differential and Sympathetic Tuning Fork Set - Investigate beat phenomena and resonance.
• Mechanical oscillator - Ideal for harmonic motion demonstrations.
• Resonating hoop - As the loop is excited through a range of frequencies, nodes and anitnodes are visible at resonance.
• Resonating reed - Resonance occurs on the six separate reed sections in a variety of modes: fundamental and overtones and at multiple frequencies.
• Wave spring - Demonstrate dramatic longitudinal or transverse waves with this Wave Spring accessory.
• Ripple tank apparatus - You can use this economy ripple tank with complete confidence in its reliability and effectiveness.
• Overhead projection ripple tank set - Your entire class can watch exciting wave experiments right from their seats.
• Dual string vibrator - Compare two different standing waves simultaneously and explain their relationship.
• Mythbusters Videos: Force and Motion | Circular Motion Video - Always intriguing, entertaining, and enlightening, Mythbusters are on a quest to uncover scientific truth.
• Heavy Duty Steel Support Rod - For use with most bases and rod support clamps.

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