A gong is a musical instrument that belongs to the group called struck idiophones. It’s a flat circular disk of bronze or brass with a convex, sometimes corrugated surface and slightly recurvated edges. It usually hangs or is placed on a special stand. It starts vibrating when struck with a soft head mallet. Type of the sound depends on a spot that is hit.
A gong is a vibrating disk, in which a two-dimensional standing wave is formed when the disk is struck. This kind of acoustic wave causes local distortions in air density that you can not only hear, but also feel with your body.
Strike the bigger gong with the mallet. Listen to the sound it makes. Place your hand near the gong’s surface, not touching it. You will feel vibrations of the air surrounding the gong. Move your hand around and explore how the intensity of vibrations changes in different places. Repeat, striking the gong in a slightly different place. Then repeat the same also with the smaller gong. Remember: never strike the very center of the gong. It could damage the instrument.