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Physical weathering is the actual breaking down of rock
by the action of natural forces
such as water, men, plants and animals.
But how do these forces wear down rock?
Here we see trees growing out of what appears to be a solid granite rock.
Actually the roots are penetrating tiny cracks in the rock
as the trees continue to grow their roots will further extend
and enlarge the cracks eventually fragmenting the rock
just as these roots have done to this rock.
Probably the most common cause of physical weathering
is due to the constant freezing and thawing of water
in and around the rocks themselves.
Let’s take a look at a simple experiment
which shows how liquid water expands when it turns to solid ice.
We fill this plastic measuring cup with water
up to the top mark.
We wanna make sure that we use a plastic container and not a glass container.
We now take our cup of water and place it in the freezer.
Here it will sit undisturbed for several hours.
Later when we view the cup
we find that the water has turned to ice
and that it is expanded almost ten percent.
We know that it is increased in sides both upward and outward
and has actually cracked the plastic cap.
But how does freezing water affect rocks?
Water frequently collects on rocks
and gets into these small openings
when temperatures drop below freezing,
the water in these cracks turns to ice and expands.
This exerts a tremendous amount of pressure on the openings in these rocks.
As temperatures rise and the ice melts back into its liquid form
it creeps deeper into the fractures
When the water freezes again
it further expands the openings in the rock.
This cycle will go on day after day, year after year
until finally a once huge mount side
could disintegrate to a pile of small rock fragments.