When a periodic wave is sent down a spring, special frequencies produce loops, or regions of constructive and destructive interference. A loop equals one-half of a wavelength, ½l.
We are now going to vibrate the spring at three different frequencies: the first one will produce two loops, the second one will produce three loops, and the fourth one will produce 4 loops.
Each time the desired pattern is produced, we will place meter sticks on the floor under two adjacent nodes. Nodes are easily identified as locations where there is NO amplitude - where the wave form seems to stay squeezed together.