Its true the ionic compounds have a higher melting point
        
                    
             
        
        
        
Tectonic plates interactions are of three different basic types: Divergent boundaries are areas where plates move away from each other, forming either mid-oceanic ridges or rift valleys. <span />
        
             
        
        
        
A) Claim 1: Plates move, which can cause earthquakes.
Explanation:
The Plate Tectonic Theory proves the claim of  plate move, causing earthquakes.
This theory states that the earth’s crust along with the uppermost mantle is formed of several thin but large surfaced rigid patch work of plate-like structures called tectonic plates.  
There are about 15 large slabs on the earth’s outer surface and constitutes the lithosphere. Lithosphere of the earth is represented by the oceanic and continental crust layer and the uppermost mantle layer.
These plates move or slide relative with each other. These plates form divergent, convergent, or transform boundaries. Slips or faults along these boundaries forms subduction zones leading to great stress. This prevents normal gliding motion resulting in earthquakes.  
 
        
             
        
        
        
When the box IS on the shelf 2m above the ground,
its potential energy is 
(weight) x (height) = (3 N) x (2 m)  =  6 joules .
THAT's the work you have to do, to lift the box up to there.