Earth science, geology: p-waves and s-waves

Tutoring earth science, p-waves and s-waves might arise. The tutor gives quick definitions.


compression waves from a seismic event (eg earthquake). These waves cause the earth to vibrate in their direction of travel. Imagine how a shock-absorber in a car moves: that models a p-wave as it reaches and passes each point.


transverse waves from a seismic event: they are similar to water waves you see in a pool.

P-waves are sometimes called primary waves, since they arrive at a distant location before the S-waves (aka secondary waves). In fact, primary waves travel about twice as fast as secondary.


Trefil, James, Ph.D., et al. The Changing Earth. Evanston: McDougall Littell, 2005.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Technology: how a metal detector works

The tutor gives a nontechnical explanation of how a metal detector functions.

Watching Curse of Oak Island on the History channel, you see them use metal detectors.

How does a metal detector work? A basic explanation is this:

  1. The search coil has electricity passing through it so that it emits a magnetic field.
  2. A characteristic of metals (as opposed to nonmetals) is that their electrons are moved by a magnetic field.
  3. As the metal object’s electrons move, they change the electromagnetic environment. It’s a kind of “rebound” effect.
  4. The detector has a detection coil that senses the electromagnetic rebound broadcast from the movement of the metal’s electrons.


Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

The Tectonic Plates: Floating Islands of Rock

Tutoring high school science, you might be asked about plate tectonics at any time.  Here is the most condensed, pragmatic explanation you’ll likely find.

To believe in plate tectonics – which, by the way, is true beyond any doubt – you need to picture this:  Earth’s surface  consists of large islands of solid rock floating on a sea of magma.  There are about 9 large plates, plus some smaller ones.  Examples are the Indian Plate, the North American Plate, the South American Plate, the Eurasian Plate, the African Plate and the Pacific Plate.

The plates more or less cover the sea of magma beneath them.  At the same time, because the plates float on the magma, they move around like toy boats in a bath tub.  When they move apart, you have what’s called a divergent boundary.  When they crash together, you have a convergent boundary.  When they rub alongside each other, going in parallel but opposite directions (perhaps like people passing each other in a crowded hallway), you have a transform boundary.  Essentially, the term fault can be substituted for boundary.

At a divergent boundary, a crack eventually forms between the plates, then magma leaks up between them, so you get volcanoes.  The volcanoes can eventually form high ridges as they continue to erupt.  Divergent boundaries are more common under the sea than on land.

At a convergent boundary, there are two possibilities.  One is a head-on collision, in which case the plates buckle as they crash (like in a car crash).  The plates deform upward, resulting in mountains.  The Himalayas are such a mountain range, caused by the collision of the Indian Plate and the Eurasian Plate.

The second possible outcome at a convergent boundary is subduction, which is where one plate rides over top and the other slides below.  If one plate is a continental one and the other is a sea plate, the sea plate slides under and the continental one rides up, forming a mountain chain.  The Andes Mountains exemplify such a situation:  there, the Nazca Plate is sliding under the South American Plate.

Although each type of boundary hosts earthquakes, a transform boundary results, especially, in earthquakes.  As the plates try to shove past each other, they get stuck.  The pressure builds, then they break loose, resulting in sudden movement – and an earthquake.  The famous San Andreas Fault at San Francisco is a transform boundary: the Pacific Plate is running NNW, while the North American Plate is running SSE, along it.

Hope this gets you started :)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

I pulled this article together from several high school textbooks:

Science Probe 10, Nelson Edition, Nelson Canada:  1996.

Earth Science, Spaulding and Namowitz, McDougal Littell:  2003.

The Changing Earth, McDougal Littell Science, McDougal Littell:  2005.