Final answer:
Tennis balls tied together and thrown will move in a coupled ballistic trajectory due to the string. Marking the center provides insight into the center of mass, which follows a parabolic path, illustrating projectile motion and dynamics principles.
Step-by-step explanation:
When you tie two tennis balls together with a string and throw one in a ballistic trajectory, you will observe that the other ball follows a similar path. This is due to the physics principles of motion and tension in the string that connects them. The motion of one ball affects the other because they are bound by the string, causing both to move through the air in a coupled motion. When you throw the linked tennis balls with a bright mark on the center of the string, this mark helps you observe the midpoint's trajectory. The bright mark can provide insight into the movement of the system's center of mass, which follows a smooth parabolic trajectory, demonstrating the principles of projectile motion and center of mass dynamics.