According to Newton's 3rd law, foot forces and ground reaction forces are equal in magnitude but what?

According to Newton's 3rd law, foot forces and ground reaction forces are equal in magnitude but what?

• A. Equal in direction
• B. Unrelated
• C. Opposite in direction
• D. Present only during swing

Answer: (C)

Newton's third law says forces come in action-reaction pairs that are equal in magnitude and opposite in direction. In gait, the foot pushes on the ground with a certain force, and the ground pushes back on the foot with the same magnitude but in the opposite direction. That is why the ground reaction force is opposite to the foot’s push. Numerically the forces match, but their directions oppose each other. This holds for each direction component: vertically the ground reaction is upward when the foot pushes downward, and horizontally the ground can push backward if the foot pushes forward. Ground reaction forces exist whenever the foot is in contact with the ground, not during swing, so the key idea is the opposite direction of the two forces.

Newton's third law says forces come in action-reaction pairs that are equal in magnitude and opposite in direction. In gait, the foot pushes on the ground with a certain force, and the ground pushes back on the foot with the same magnitude but in the opposite direction. That is why the ground reaction force is opposite to the foot’s push. Numerically the forces match, but their directions oppose each other. This holds for each direction component: vertically the ground reaction is upward when the foot pushes downward, and horizontally the ground can push backward if the foot pushes forward. Ground reaction forces exist whenever the foot is in contact with the ground, not during swing, so the key idea is the opposite direction of the two forces.