Fluid Rigid Body Motion

Tanker truck traveling down a road.

As I was driving on the interstate today I passed a tanker truck. I was mindful that if he had a partially filled tank, the fluid could behave in ways described by fluid in rigid body motion. If the tanker truck began to break or accelerate, the fluid in the tank would form either a triangle or parallelogram when viewed from the side. Measuring the dimensions of this triangle or parallelogram would allow you to determine the amount of force the fluid is undergoing. This becomes practical knowledge when you need to know the maximum  amount of acceleration or deceleration a tank can undergo without spilling potentially hazardous chemicals.