Final answer:
The illusion of weight and volume in animation is achieved through principles such as squash and stretch, as well as the manipulation of timing.
Step-by-step explanation:
The action that gives the illusion of weight and volume to a character as it moves is the thoughtful use of animation principles, such as squash and stretch and timing. These principles contribute to the depiction of weight and the interplay of mass and volume in motion. For example, an animator might squash a bouncing ball as it hits the ground to suggest its mass and the force of impact, and then stretch it as it rebounds, indicating its elasticity and volume. Similarly, the careful control of timing can illustrate the weight of a character; slower movements suggest a heavier object, while quicker actions imply lightness. This manipulation of elements in art is akin to the way objects like wood float in water due to their density, mass, and volume interrelationship. Likewise, the perception of weight can be affected by external forces, as described by Einstein's example of feeling heavier or lighter in an accelerating high-speed elevator due to the change in gravitational force acting upon the body.