Physical weathering crush a rock's physical structure changing its appearance by friction or impact, therefore, to provide a demonstration of this principle I would take the hammer and smash the rock changing its appearance with the impacts
In contrast, chemical weathering occurs when a chemical reaction of any kind alters a rock's chemical composition changing its appearance through erosion and degradation, therefore, to contrast this phenomenon with the physical weathering I would put acid on the rock to demonstrate the chemical degradation
A fall line is an upland region of the coastal plains meets and the term states that lots of rivers fall from this Piedmont to the coastal plain making rapids with waterfalls.
These falls are important as for the settlement as they block the ocean going ships from entering in any further upstream and also provided water power to run the region industries.