Final answer:
The forces on a biker turning a corner at a constant speed of 12 miles per hour are unbalanced due to the need for a centripetal force to change the direction of the velocity. This force is provided by friction and directed through the center of gravity for stability.
Step-by-step explanation:
A biker maintaining a constant speed of 12 miles per hour around a corner is experiencing unbalanced forces. During a turn, even though the speed is constant, the direction of the velocity is changing, which means there is acceleration (specifically, centripetal acceleration). According to Newton's second law, an acceleration occurs when a net external force acts upon an object. In this case, the unbalanced force is the centripetal force that is necessary to change the direction of the biker's velocity. This force is provided by the friction between the tires and the road, which acts perpendicular to the direction of the biker's velocity at every instant of the turn. It's important to note that the force exerted by the ground must be directed through the center of gravity to maintain stability, and the force on the wheel can be broken down into a vertical component that balances the weight of the system and a horizontal component that provides the centripetal force.