Squash and Stretch In Gesture or Figure Drawing

Many students in Japan who look at my drawings often say "it looks like it has volume" or " it looks like it's moving".  

Many people have heard about  "squash and stretch" in drawing.  Often people will show it in the bean or flour sack/ rice bag model.  

Some people apply this in a very graphic way.  Nothing wrong with that, but if people are interested in making their drawings look more believable, then weight should be considered in the volumes. 

In animation there is the famous "bouncing ball" model to show squash and stretch as it applies to weight and time.  

With weight we have two forces applied to the forms: "expansion" or "contraction". 

If we had a piece of chewing gum on the floor.  It just sits there because there are no aggressive forces acting on it.  However if we push in it, the forces applied need to escape so the forces push the volumes outward as the gum expands.  

Let's now imagine that the gum is now stuck to the floor and we want to pull it away.  Since then gum is stuck and will not release from the floor part of it will stretch and thin out.  

Volumes closer to the ground tend to spread out and expand, while things pulling away tend to thin out or seemingly contract inward.  

How does this apply to drawing the figure?

When I draw a figure crouching on the ground, I tend to expand the muscles and draw them rounder as I imagine the center of gravity being heavier.  My lines are slower and heavier as well.  

However when I draw a dancer lifting upward, I imagine the dancer pulling away from gravity and my lines are faster and thinner. 

Volumes affected by gravity will be drawn rounder and heavier.  Lines that are resisting gravity will be thinner.  

Imagine the forces of gravity working on everything you draw.