I was thrilled to find a copy of Action Analysis for Animators on my desk – fresh off the presses. Due out in April, Chris Webster examines the fundamentals and subtleties of action analysis and applies it to animation. In celebration, we decided to post an excerpt from Action Analysis for Animators to give you a peek at whats to come. This excerpt explores analysis of pushing and pulling in animation.
As with many actions, the level of force required to complete an action, such as moving an object, determines the nature of the action. Generally speaking, the most efficient method using the minimum of effort applies for all actions.
Pushing a button may require only a very small movement that extends no further than the fingertip. A stronger push may involve the movement of the entire arm, incorporating movement at the wrist, elbow, and shoulder. Pushing an object that offers greater resistance may require the use of the entire body in a way that employs the weight of the body to apply additional force beyond that applied by the effort of the muscles. During this type of push the angle of the body may be positioned not directly above the feet, as in a normal standing or walking gait, but extended beyond the position of the feet in the direction of the object. In this fashion the weight of the body is used to provide the additional force.
Pushing a static object requires a degree of force to overcome the inertia made up of a combination of the object’s mass and any friction between the object and the points of contact with any surface on which it sits or has contact. The more resistance there is at this point, the greater the force required to move the object. There will be a greater level of potential friction between an object sitting on a heavily textured or soft surface than one sitting on a hard, flat, and slippery surface such as ice. Attempting to push an object with a flat bottom may require more effort than pushing a heavier object that either has less friction or is designed to aid smoother movement, such as objects that possess runners, blades, or wheels.
Pushing a wheeled object such as a wheelbarrow requires far less force to overcome inertia and enables far greater loads to be shifted for the same degree of force. The wheel provides a lower level of friction between the load object and the surface through the rolling action as opposed to a sliding action of two flat surfaces. Once inertia has been overcome, forward movement may be maintained by the steady application of force, created as continuous pressure is applied—in this instance, as the figure walks forward. If the weight is very heavy, the pushing figure will tilt forward from the upright position to gain greater purchase with the feet
Many of the same issues that are evident in a pushing action may also be seen in a pulling action: the need to overcome the inertia of an object and the amount of friction between the object and surfaces and the use of body weight to increase force. Pulling may be undertaken simply by the movement of the fingers. Greater forces may be exerted simply using the hand with a movement at the wrist. Pulling an object by the use of rope, if not too heavy, may be undertaken by a hand-over-hand action that can only entail the use of the arms. This action entails each arm working in turn to pull on the rope toward the body, one arm pulling on the rope while at the same time the second arm extends forward to gain a grip on the rope in preparation for a subsequent pulling action.
Heavy objects may be moved through a pulling action using the body weight as part of the pull. This can be achieved by the figure facing the object while holding the rope and extending the body away from the object, thereby applying a force using the weight of the body.
Alternatively, the body may be turned away from the object with the rope placed over the shoulder and the hands gripping the rope firmly placed close to the body before the figure commences to walk forward. This may entail the body being angled in a position forward of the feet. In this way greater purchase may be gained by the feet on the floor, thereby exerting greater force.