What is the "action line" of force in physics and how to understand it

What is the "action line" of force in physics and how to understand it

The action line of force is the ray drawn along the action direction of the force, but it is more intuitive on the graph, which does not exist in the real world

What is the action line of force

In the schematic diagram, the line where the arrow representing the force is located is

What is the physical meaning of the water head line

The connection line at the top of the imaginary water column representing the water head of each particle on the same streamline, where the water head represents the potential energy of water (fluid), and the dimension of the water head is length

What is the action line of force in lever?

A straight line drawn along the direction of the force through the point of action of the force