The illusion of weight is all important in animation. Without it your characters will appear to be... well, weightless. Gravity acts upon all of us. If you lose your balance, you will fall to the ground. If you drop a pencil it too will fall down to the ground. We would certainly be quite startled if you dropped something which you knew should fall to the ground but instead of it falling, it began to float into the air. That would defy everything that we know about gravity.
If you stand in one spot, bend down and then jump straight up into the air, you might go up about 6 - 8 inches then drop back down to the ground. When you land, your knees bend in order to absorb the shock of landing. This is similar to the squash principle discussed earlier. Without the squash action, the character would appear stiff and weightless. This was common in all the early animated cartoons from 1900 through to the early 1930s.
As the animators became more experienced, (and the budgets for the cartoons got higher) they began to incorporate the observations that they made of the actions of the other animators acting out their scenes. These observations led to the incorporation of the principle of overlapping action (well talk more about this in a later lesson when we get into some animation principles).
Weight in your drawing can be conveyed through the use of the volume of your characters and the line quality you put into the final drawing (which well also talk about later).
The balance of the character in the drawing can also create the illusion of weight or shatter it. Check out the examples to see what I mean.