00:01
So in this question we're given a velocity field.
00:04
V equals p cos theta in the r direction, minus p sine theta in the theta direction.
00:13
And now we're going to use the unit vector in the r direction.
00:20
So let's just draw a little picture.
00:24
So here's a point.
00:28
And we've got r and theta hat.
00:33
And we can express these in terms of the cartesian.
00:36
Unit vectors x hat and y hat by resolving onto these particular axes and we're going to find that r hat is going to be cos theta x hat plus sine theta y hat and theta hat is minus sine theta x hat plus cos theta y hat so now we can expand this velocity in cartesian coordinates and it's going to be p cos squared theta x hat plus p cos theta sine theta y hat that's the first part and then minus p sine theta theta theta hat gives us plus p sine squared theta x hat minus p sine theta cos theta y hat now these cancel and these add and we can use the trigonometric identity cos square theta plus sine square theta is one to give us that v is just p x hat so the velocity is constant and pointed in the x direction.
01:43
So this is actually just a constant velocity field.
01:46
The streamlines are going to be defined by the equation dx of the streamline over the x part, which p is equal to d .y of the streamline over the y coordinate, which is the y coefficient, which is zero...