Final answer:
It is false that gibbons are knuckle-walkers; they walk upright on two feet when on the ground. Also, it is true that a person accelerates while walking due to the force exerted on the ground, which responds with an equal and opposite force, enabling walking according to Newton's Third Law of Motion.
Step-by-step explanation:
The statement that gibbons are knuckle-walkers when on the ground is False. Gibbons are known for their brachiation, which involves swinging from tree limb to tree limb using their arms. When gibbons move on the ground, unlike other apes such as gorillas and chimpanzees that do knuckle-walk, gibbons walk bipedally, meaning they walk upright on two feet.
In reference to Newton's Third Law of Motion and the concept of walking, the statement that a person accelerates while walking on the ground by exerting force is True. When a person walks, they exert a force (F₁) on the ground. According to Newton's Third Law, the ground then exerts an equal and opposite force (F₂) on the person. While the two forces are equal in magnitude and act in opposite directions, only the force on the person contributes to walking because the forces act on different systems, and hence the net force acting on the person is nonzero, allowing the person to move forward.