I've just come across an excellent teaching activity by Noel Jenkins of Juicy Geography about earthquakes in San Francisco using Google Earth. It uses ground overlays to illustrate areas of liquification danger and earthquake amplification danger. Noel says he's tested the activity in class and that it could be used to cover GIS teaching too.
Opacity Slider: One of the functions that is used in the activity is the 'opacity slider', this changes the transparancy of a ground overlay. I thought it worth exactly how to use the opacity slider as its useful in lots of teaching situations:
1] Open the file that goes with the lesson plan
2] Expand the folders in the Places column until you have the data overlays folder open (click the plus buttons on the left of the folders to do this)
3] The elements showing in this folder are all ground overlays, basically images that lie over the Google Earth topography like a table cloth. You can tell this by looking at their icons in the places column - a sheet overlying another sheet.
4] Tick one so it shows on screen. Notice that it also goes blue, this means it's selected.
5] Click the square icon at the bottom of the Places column to the right of the magnifying glass. A slider appears, moving the circle changes the transparency (or opacity) of the overlay.
Adjusting the opacity allows you to see the true image of the ground below and or see another ground overlay more clearly.
Useful Supporting Videos:
the above clip shows someone lecturing at the time of an earthquake (I think in California). If you replay it and watch carefully you can see that most of the students run for the door and only one student does what they've been taught and dives under the desk.
The clip below shows an illustration of liquefaction, when shaken, the sand behaves like a liquid and more dense items (the building model) will sink into it. You can easily do something similar with a box of rice which you shake by hand, you don't need the motor shaker.
and this is what it looks like in real life. The water coming out is a more complicated effect to explain but is related to liquefaction occurring.