Tie the fishing line to a chair. Slide the slinky onto the fishing line, and then tie the other end of the fishing line to another chair. Pull the chairs apart until the line is taut. Optional, rest the slinky on a smooth table top. If you use a table top, use only 1/2 of a plastic slinky, otherwise friction will make the experiments difficult.
Grab the ends of the slinky in your hands. Stretch the slinky to between 1 and 2 meters long. Move your hands together and then apart, just as if you were clapping. Notice the motion of the slinky. Your hands move a lot while the center of the slinky moves very little. The center is a node. You can attach a small flag of masking tape to the center of the slinky to make it easier to see that the center is not moving.
Next notice the spacing between the slinks (turns) of the slinky. When the slinks are jammed close together the slinky models high pressures in a gas, where the atoms are closer together. When the slinks are far apart ,the slinky models low pressure in a gas. Let's call closely spaced slinks high pressure and widely spaced slinks low pressure. Notice that the pressure change is greatest at the center where the slinks alternately bunch-up and spread apart, and where the side to side motion of the flag is the least. Count the rhythm of this motion: 1,2,3,4,1,2,3,4,... Move both hands in the same direction, if the slinky stretches right-left move both hands to the left then to the right. (One of our teachers described this as the sound of one hand clapping twice.)
Notice the motion of the slinky which is called longitudinal motion. Find the frequency of hand motion that produces the largest motion of the center of the slinky for the smallest motion of your hands. Count the rhythm of this motion: 1,2,3,4,1,2,3,4,... Notice that the center of the slinky is an antinode, your hands are nearly nodes. The flag marking the center whips back-and-forth. Notice that in the center the slinky moves back and forth but the spacing between the slinks near the center does not change. The center is an antinode of motion but a node (a place with no change) of pressure. At the nodes of motion near your hands however the slinks bunch together and then spread apart: the pressure changes a lot. The hand-held ends are antinodes of pressure. Notice also that when one hand is at high pressure the other is low. The ends then swap. The high pressure hand becomes a low pressure and vice-versa. In other words, the slinks bunch up near one hand while they spread out at the other.