Analogies are a useful instructional strategy, especially in the science classroom. They can serve both to motivate student interest while also developing a conceptual understanding of topics that can’t be easily explored through direct experiences, such as labs and demonstrations. For example, the visual analogy presented on this poster serves both a motivational function by combining seeming discrepant concepts while also connecting a familiar concept (analog) to an unfamiliar idea (target). In this case, the analog is a drop of water hovering above and then falling into a pool of water, while the target is an earthquake. While such analogies are useful to emphasize shared attributes it is possible for students to map attributes that are not shared as well. To maximize the benefits of an analogy while also minimizing the dangers the use of the Teaching with Analogies (Glynn et al., 1995) strategy is highly recommended. These steps include;
1. Introduce the target concept
2. Review the analogue concept
3. Identify the relevant features of target and analogue
4. Map similarities between the target and analogue
5. Indicate the limitations of the analogy
6. Draw conclusions
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| Analog (Familiar situation) | Target (Science Concepts) |
|
Dripping water and ripples |
Earthquakes |
| is (are) like | |
| A water droplet suspended above a pool of water | Potential energy stored elastically in rocks beneath Earth's surface as they deform from the motion of Earth's plates |
| The water droplet grows from the slow leak. Eventually it becomes too heavy and overcomes the forces suspending it. | Potential energy builds in rocks as plate motion continues. Eventually it overcomes the strength of the rock. |
| The water droplet falls striking and temporarily deforming the surface of the water | The rock suddenly slips/breaks (potential energy is converted to kinetic energy) temporally deforming Earth materials |
| Because water is an elastic medium, the particles in water are deformed, physically interact with their neighbors and return to their original position. Thus, energy is transported not water | Because Earth is an elastic medium, the particles in Earth are deformed, physically interact with their neighbors and return to their original position. Thus, energy is transported not Earth material |
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Via the process above energy propagates outward from the sources across the surface as ripples. Note: In this example unseen is a pressure wave that propagates through the water ahead of the ripple shown. |
Via the process above energy propagates outward in all directions from the earthquake hypocenter as body waves. When this energy reaches the surface, surface waves are generated. The poster shows the surface effects of both body and surface waves propagating outward from the epicenter. |
| Ripples in water travel along the phase boundaries between water/air and decrease in amplitude with depth | Surface waves travel along the phase boundary between Earth/atmosphere and decrease in amplitude with depth |
| As a ripple propagates, water particles have both longitudinal and transverse motion | As a Rayleigh wave (one type of surface wave) propagates particles have both longitudinal and transverse motion |
| Analog (Familiar situation) | Target (Science Concepts) |
|
Dripping water and ripples |
Earthquakes |
| is (are) NOT like | |
| A water droplet grows from a slow leak over a relativley short time period, perhaps over the course of seconds or minutes. | Potential energy builds very slowly in rocks as Earth's tectonic plates move ~3-5 cm/year. |
| Ripples are most like surface waves as both travel along the phase boundary. |
Ripples are not like body waves (Primary and Secondary waves). These seismic waves radiate outwards in all 3-dimensions and travel through Earth. |
| Particle motion for water ripples is prograde |
Particle motion for Surface waves is retrograde for Rayleigh waves and perpendicular to the direction of wave propagation for Love waves. Particle motion for Body waves is parallel to the direction of wave propagation for Primary waves and perpendicular to the direction of wave propagation for Secondary waves. |
| Ripples expand in nearly concentric rings because water is essentially homogeneous |
Seismic waves expand in only roughly concentric rings/spheres. This velocity of the seismic waves, and intern the shape of the rings/spheres is influenced by the geology of the Earth materials the waves are traveling through. Some materials speed up waves while others slow them down. |
| Ripples are relatively slow |
Seismic waves in Earth travel approximately 100 times faster than water waves |
| A falling droplet of water strikes the surface of the water to create ripples | Earthquakes occur below the surface at the hypocenter and propagate outwards. Surface waves are generated went the body waves interact with the surface of Earth |
Other general differences:Physical scale, scale of the energy released, material/composition (water & Earth), Earthquakes are not generated from falling water on Earth, a water droplet may build up in seconds while the stress for an earthquake can accumulate for hundreds or thousands of years, stresses for earthquakes are built up from within Earth.
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