Enigma 4 resolved : "Look" on the bottom of the sea

A great first!... measures wave speed with piezo from ‘seismology@school’ in the core lab of JR!

After measurements in the lab of the ship, we obtain the following results:
Wave velocity is not the same in the various materials found aboard the JR!
In the gabbro the waves propagate very fast (speed around 7km / s). For other materials, it is 2km /s for sediments, 4 km/s for the aluminum bar (finally not so fast!). In the bar foam, waves propagate more slowly 0.4 km / s.

Given these rates, the length of the bars will not affect the ranking of the different materials.
So for this race waves, we find upon arrival in the first position gabbro, then aluminum and finally sediment and foam.

 

Thus, with this simple experiment, we show that the waves do not propagate at the same speed in different materials. This could be due to some physical parameters such as density. This will be the subject of one of the next enigma !
 

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W4_seismic_corrige_en.pdf563.66 KB