This easily built classroom apparatus is ideal for gaining a better understanding of how earthquakes work and how they are recorded. The apparatus consists of a heavy object that is dragged steadily with an elastic cord. Although pulled with a constant velocity, the heavy object repeatedly slides and then stops. A small vibration sensor, attached to a computer display, graphically monitors this motion, ... Full description.

In this activity, students create their own P- and S-wave travel chart and develop a better understanding of the relationship between the two wave types, travel times, and travel distances. Full description.

The properties of a rheid represent essentially all Earth materials: they behave elastically over short time scales and plastically over long time scales. In this demonstration, silly putty is used to help explain these properties as well as the yield strength of a material. Full description.

This demonstration elucidates the concept of propagation of compressional waves (primary or P waves) and shear waves (secondary or S waves), which constitute the seismic waves used in locating and modeling earthquakes and underground nuclear explosions, and for imaging the interior structure of the Earth. The demonstration uses a slinky, pushed along its axis to create a compressional (longitudinal) ... Full description.

This demonstration of how seismic waves reflect when they encounter a change in rigidity or incompressibility requires a helper to hold one end of a stretched-out slinky as stiffly as possible. The helper represents a material with a much greater rigidity than the slinky; waves can then be sent and reflected along the slinky. The site also discusses a demonstration of reflection from a less rigid ... Full description.

This site describes a demonstration of how the interference of seismic P (primary, compressional) and S (secondary, shear) waves cause standing waves such as surface waves in the Earth. The demonstration focuses on the P and S waves that are bouncing back and forth in the vertical direction in the Earth. Using a slinky, different frequencies are used to create different modes of standing waves. The ... Full description.

This participatory demonstration of the influence of rigidity on the speed of seismic waves helps students understand the relationship between the speeds of seismic P and S waves and the rigidity (the resistance to shear deformation) and incompressibility (resistance to compression) of the medium. The demonstration requires only a watch or stopwatch. To create the waves, students stand side-to-side ... Full description.

This demonstration of average density uses understandable units of total mass and volume of the Earth. The required supplies are a can of beer or soda and a 1-pound bag of pretzels. By imagining, for instance, 4.4 bags of pretzels fitting into a beer/soda can, students can better visualize the average density of the Earth. Full description.

This demonstration uses a gyroscope (a bicycle wheel works well), string, and a turntable (optional) to show how the equatorial bulge of Earth causes precession. By balancing the spinning bicycle wheel on one hand, and pulling a string attached to the top axle with the other, the axis of the wheel traces out a circle (precesses). The site also explains how the moment of inertia is related to torque ... Full description.

This is a demonstration of the Core Shadow Zone of the Earth. Using a clear or translucent half-sphere held in front of a light source, the refracting properties of the core and how it generates the shadow zone on the surface are illustrated. Full description.