Sound Waves!

Look at the diagram at the end of the video. A capacitor has two plates that conducts electricity (aka. conductors) and store electric charges. An insulator (aka. dielectric) is in between the two plates, where it does not conduct electricity.

Since our bodies are conductors, our hand acts as one of the plates and the antenna is the other plate! And the air is the insulator!! Therefore, when you move your hand away and closer to the antenna, you’re changing the distance between the two capacitor plates.

As we increase the separation, capacitance and charge decreases along with pitch.

Fun fact: This was invented by Lev Sergeyevich Termen in 1920.

PART 1: How are these patterns being formed from these “pleasant” sounds? This demonstration is called the Chladni Plate. People commonly use a square metal plate to perform this experiment; however, the shape does not matter as long as it has a fixed constraint attached. Therefore, you can have the same effects with a putty knife, a bow, and sand (just like this!). In this case, the fixed constraint was having somebody else hold down the handle of the putty knife. The bow is used to produce vibrations to excite the plate at different resonant frequencies. Every object has its own natural frequency; therefore, each frequency has its own standing wave. As the plate begins to vibrate, the sand travels toward the parts of the plates where it is not moving, which are the nodal lines. The standing waves create nodal lines which is where the sand end up locating and resting, creating the unique patterns.

PART 2: I noticed that when a lower pitch is played, the sand usually forms an arch. However, when a higher pitch is played, the sand forms small circles or pods. What did you notice?

Striking the singing bowl’s rim with a mallet is a demonstration of transverse waves and resonance. Through observation, the sound waves are manifested on the water’s surface through the nodal points. The first point is where the mallet hits the bowl, and the second point is exactly opposite of that. The third and fourth points are located in the middle of the first and second points. The harder you strike it, the pattern of the water emerging will become more visible. When the water emerges in the center of the bowl, they collide with each other, cancelling each other out.