WEBVTT

00:00:00.720 --> 00:00:03.360
This week, we will use
the concept of momentum

00:00:03.360 --> 00:00:06.030
to analyze some more
advanced situations.

00:00:06.030 --> 00:00:09.630
Namely, systems in which there
is a continuous flow of mass

00:00:09.630 --> 00:00:12.510
rather than just the
motion of discrete objects.

00:00:12.510 --> 00:00:14.940
The classic example
of this is the thrust

00:00:14.940 --> 00:00:17.940
due to exhaust from
a rocket engine.

00:00:17.940 --> 00:00:21.090
Once again, we will appeal
to a differential analysis

00:00:21.090 --> 00:00:22.530
technique.

00:00:22.530 --> 00:00:26.670
Breaking the flow down into a
large number of small elements,

00:00:26.670 --> 00:00:31.830
analyzing one of the elements in
detail, and then generalizing.

00:00:31.830 --> 00:00:34.770
This is an important
example of a situation where

00:00:34.770 --> 00:00:38.000
the point mass form of Newton's
Second Law of Motion-- f equals

00:00:38.000 --> 00:00:40.560
ma-- is inadequate,
and one must instead

00:00:40.560 --> 00:00:42.900
use the more general
form of the law-- f

00:00:42.900 --> 00:00:46.560
equals dpdt-- or the
force is equal to the time

00:00:46.560 --> 00:00:48.525
derivative of the momentum.