Objective: To demonstrate how understanding the properties of seismic waves leads to understanding the composition of earth’s interior.
Standards: Properties of Earth Materials (physical and chemical properties of rocks and soils, water, and gas), Structure of Earth System (layering and properties of Earth’s internal structure; plate tectonics and its relation to earthquakes), Transfer of Energy (energy types, characteristics, and transfer properties), and Interactions of Energy and Matter (waves have energy and can transfer energy when they interact with matter).
Materials: One 2 qt. bowl, glass soft drink bottle, and pencil.
(1) Fill the bowl approximately half full with water.
(2) Set the bottle in the center of the bowl of water.
(3) Tap the surface of the water several times near the side of the bowl with a pencil
Science Behind It: As waves ripple out from where the pencil tapped the water to the glass bottle, most reflect back towards the pencil. These waves of energy that are not able to move through the bottle are analogous to secondary (S) waves from an earthquake. S waves arrive after primary (P) waves during an earthquake because they are slower and have less energy than P waves. S waves have the ability to move through solid objects but cannot move through liquids. The S waves move through the solid parts of Earth’s interior, but just as the water waves hitting the bottle, they are reflected back to the epicenter by Earth’s liquid core. P waves travel completely through the center of the Earth, but S waves are reflected back, indicating the inner part of the earth is liquid material.