The point of this activity is to understand vibrations and sound waves and how they move, affecting the air molecules surrounding them. There will be a tuning fork used to demonstrate sound waves and how they affect the surrounding air molecules, in this case salt on a cup. The next small activity is hooking strings to a fork around your hear, and hitting it against the table to see how the sound has amplified. Next, the students will move a slinky back and forth and observe the motion. Finally they will take their fingers and move it around the rim of a wine glass and listen closely. I can see them having difficulty with the wine glass portion, and not getting it to make a sound. Also, hitting the tuning forks hard enough to vibrate for a long enough time to make the salt move on top of the cup.
What you are hearing from these instruments throughout the activity are pressure waves. Waves are periodic motion: longitudinal (sound) and transverse (light). The properties of sound waves are the amplitude (loudness) and wavelength (pitch). Vibrations of an object cause the surrounding air molecules to start vibrating, in this case the salt was shook on top of the cup. These vibrating molecules create pressure waves that travel in the direction of the sound. There are also two different types of waves the students saw with the slinky activity: longitudinal and transverse waves. Coils that move left/right are longitudinal and coils that move up/down are transverse waves.