Which of the following forces acts equally in opposition during motion, contributing to balance?

Ground reaction forces play a crucial role in maintaining balance during movement. When a person is in motion, whether running, walking, or performing any other activity, the ground provides an equal and opposite force that acts through the contact points between the feet and the surface. This is described by Newton's third law, which states that for every action, there is an equal and opposite reaction.

These forces help stabilize the body and are essential for activities that require balance and coordination. For instance, when you push off the ground to take a step, your foot exerts a downward force on the ground, while the ground reacts with an upward force that helps propel you forward. This interaction ensures that the body remains balanced and controlled during movement.

In contrast, other forces mentioned do not directly contribute to maintaining balance in the same way. Friction assists in providing grip and preventing slipping, muscle forces control movement, and inertia relates to the body's resistance to changes in motion. However, it is the ground reaction forces that specifically provide the necessary support and counterbalance during dynamic activities.