What are the similarities and differences of primary and secondary waves?

Answer 1

The terms Primary wave and Secondary wave are used in seismology (the study of things like earthquakes). These are two different sorts of waves which can travel through the earth and be detected some distance away. The P wave travels faster and gets there sooner so it is called "Primary" (First). The other follows and gets there later so is called "Secondary" (Second). The primary wave is called a compression wave like a sound wave travelling through air. Each particle in the medium (substance wave travels through) pushes on the next one and builds up pressure which pushes back. In other words, the particles move back and forth along the same direction as the wave travels. The S wave is also called a shear wave. This is where the particles move sideways to the direction of motion of the wave. P waves have a typical speed through the earth at between 6 and 10km/sec (4 and 6 miles/sec). S waves travel between 3 and 7km/sec (2 to 4 miles per second). It is the study of these waves after earthquakes that allowed us to discover what the interior of the earth is made of.

Answer 2

Similarities:

• They are both seismic waves that transmit energy.
• They are both "body" waves.
• Their velocity is affected by the density of the material through which hey travel.

Differences:

• S-waves are transverse waves where as P-waves are longitudinal waves.
• As P-waves are longitudinal or compressional waves they are able to travel through liquids and so can pass through the Earth's outer core. S-waves are not able to travel through liquids.
• P-wave velocity is affected by the bulk and shear modulus of the material through which it is travelling, S-wave velocity is affected by the shear modulus of the material only.
• P-wave velocity is higher than S-wave velocity for a given material.