Final answer:
A kangaroo's jump and subsequent return to the ground illustrate Newton's third law of motion and principles of gravity; bending the hind legs to cushion the landing effectively demonstrates these physics concepts.
Step-by-step explanation:
The phenomenon of a kangaroo returning to the ground after jumping due to the force of gravity illustrates Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. When the kangaroo jumps, the Earth exerts a gravitational force on the kangaroo, pulling it back down; this gravitational force represents the unbalanced force that causes the kangaroo not to stay aloft. The kangaroo's hind legs bend to cushion the impact, reducing the force on its bones by increasing the time over which the force acts, demonstrating the practical application of physics principles in nature.
Newton's third law, along with his law of universal gravitation, explains why objects are attracted towards Earth with a certain acceleration due to gravity, regardless of their mass. The force of gravity is dependent on the masses involved and the distance between them, a concept that simplifies the understanding of movement and interaction of bodies in space.