# B Series expansion of velocities

Tags:
1. Apr 1, 2017

2. Apr 1, 2017

### Staff: Mentor

U is the velocity in the x direction. And they used a Taylor expansion at 2:38 into the video to get the expression you see. They drop the other terms of the series as negligible when $\Delta x$ tends to zero along with the other deltas t and y.

3. Apr 2, 2017

### mech-eng

In 2 Δv disappears instead du/dx and Δy appears.

Thank you.

4. Apr 2, 2017

### pasmith

They swapped the order of the first two terms in addition to using $\Delta u \approx \frac{\partial u}{\partial x} \Delta x$ and $\Delta v \approx \frac{\partial v}{\partial y} \Delta y$