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This week, we will use
the concept of momentum

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to analyze some more
advanced situations.

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Namely, systems in which there
is a continuous flow of mass

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rather than just the
motion of discrete objects.

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The classic example
of this is the thrust

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due to exhaust from
a rocket engine.

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Once again, we will appeal
to a differential analysis

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technique.

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Breaking the flow down into a
large number of small elements,

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analyzing one of the elements in
detail, and then generalizing.

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This is an important
example of a situation where

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the point mass form of Newton's
Second Law of Motion-- f equals

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ma-- is inadequate,
and one must instead

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use the more general
form of the law-- f

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equals dpdt-- or the
force is equal to the time

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derivative of the momentum.