Sounds even poetic... And abstract.

"So.. How you will explain?"

Well... How it works! If you analyze the motion no matter what, there is always an applied force. Can be the Earth's gravity or even an object or person. This leads to two types of force that can be applied: External Force and Internal Force.

External Force is about everything that comes out of the body you are analyzing. It can be a wind, or a person pushing you, or even a guy giving a punch in your face.

Since the head received the punch, it will lead the movement. After it, will be the neck, the upper body and so forth.

Internal Force is about a purpose with their own decisions. In this case, the action usually begins at the hip. But the point is, if you want to bring live into a character, that's how you will succeed. Because is the Internal Force who show the character is living, breathing or thinking!

This emphasizes to encourage us to always have on hand many references as possible and carefully analyze each action of motion.

Here my final assignment studying the torso and using an external force: