Node (physics)
From Biocrawler, the free encyclopedia.
A node is a spatial locus along a standing wave where the wave has minimal amplitude. This has implications in several fields. For instance, in a guitar string, the ends of the string are nodes. By changing the position of one of these nodes through fretwork, the guitarist changes the effective length of the vibrating string and thereby the note played. The opposite of a node is an anti-node.
There are two types of wave propagation: lateral and transverse. An example of the former is the guitar string, or light. You can easily see the displacement nodes, because they have minimal amplitude.
An example of a transverse wave is sound. With a transverse wave, the amplitude extends in transverse direction, so in the direction of wave propagation. There also exist standing transverse waves, in a flute, for example. The air in the flute moves back and forth, but it doesn't move at the closed end. Only the pressure changes there. This is a node, again. The open end of a flute is an antinode, because the air displacement is the largest here. When you change the way you blow the flute, you might hear a sound higher than the original. Now you have a node somewhere inside the flute. The air moves to and from this point, so at the node itself only the pressure changes.
In this flute, you could also interpret the nodes to be antinodes and vice-versa. This is when you look at the pressure. The pressure does not change at a node (althought a lot of air passes there) and the pressure changes the most at an antinode (the closed end of the flute).
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