Direct students to make observations concerning the sound they hear. Ask them to describe the path sound waves are taking to their ear. Ask students to predict what they will hear, if anything, when the end of the pencil is placed in their ear. Sound travels more than seven times as fast through the string and the pencil. The more rigid a substance is, the faster sound travels through it.
Sound waves are a series of compressions and rebounds of the medium through which it is traveling.
The molecules of solid objects are more tightly packed together than liquids or gases. The sound traveling through the string is much louder because most of the wave energy is directed through the string only, and not dissipated in surrounding air. Use the slinky to illustrate a compression wave. Students will want to move the stretched slinky up and down. Compression waves are formed by pushing a stretched slinky toward the other end.