Higher - The gradients of two perpendicular lines will always multiply to make –1. Make sure you are familiar with finding the equation of a line and calculating gradient to understand equations ...

Learn how to find equations of parallel lines, work out the gradient of perpendicular lines, and prove that given lines are parallel or perpendicular.

In some cases, the thinning of the interface also generates a gradient in surface tension. Essentially, the water drains out, leaving a higher soap concentration.