Final answer:
Animals counteract their weight or gravity with the normal force, which is the support force exerted by a surface when in contact with it. This force is equivalent to gravity, allowing the animal to stand or move without falling.
Step-by-step explanation:
The force that animals use to counteract gravity, or their weight, is called the normal force. This is the support force exerted by a surface when an animal or object is in contact with it. For example, when gravity pulls an animal down, its muscles exert force to push against the ground, maintaining balance and posture. Similarly, when a dolphin jumps, it moves its muscles to exert a force on the water, and the water pushes back with an equal force, allowing the dolphin to move through the air.
To illustrate further, consider an animal standing still. The ground pushes back with a force equal to the animal's weight due to the rigidity of the surface, just like a table slightly deforms and provides a restoring force when a weight is placed on it. The point at which this restoring force equals the weight, the net external force is zero, resulting in the animal or object remaining stationary.