How would you classify a wave that moves back and forth like a slinky?

A wave that moves back and forth like a slinky is classified as a longitudinal wave. In longitudinal waves, the oscillations of the medium (such as the coils of the slinky) occur in the same direction as the wave travels. This results in areas of compression, where the coils are pushed closer together, and rarefaction, where the coils are spread farther apart.

This type of wave is often contrasted with transverse waves, where the oscillations occur perpendicular to the direction of wave travel, such as in waves on a string or electromagnetic waves. The behavior of the coils in a slinky demonstrates how particles of the medium move back and forth along the same path as the wave propagates, making this example a clear representation of longitudinal waves.

Understanding the characteristics of longitudinal waves is key in various scientific concepts, such as sound waves, as they also transmit energy through compressions and rarefactions in the medium.