In many problems throughout this class,
we will find it useful to consider
how the mass of an object is distributed
throughout the object.
To do this, we will define a small piece of that object
and then consider the mass that's contained
within that small piece.
For an object in one dimension, the differential element
of length is delta l.
And that length contains a certain amount
of mass, delta m.
We could also have a linear object
in the shape of an arc or just an arbitrary path.
For an object in two dimensions, we
have an area element, delta A, that contains a mass delta m.
For our volume, we have a volume element, delta V,
which contains a certain amount of mass.
In this case, we can write the volume element delta
V as the area A times this delta x.