The braking force coefficient initially increases and then decreases with wheel slip due to the conversion of momentum to heat, which affects friction and can lead to brake fade. As brakes heat up, their effectiveness diminishes, resulting in a softer brake pedal and potential issues like boiling brake fluid and tire overheating. The curve shape reflects the difference between static and kinetic friction, where maximum traction occurs before the tire begins to lock up. Once slipping starts, the contact patch and pavement move at different velocities, reducing traction. Understanding this interaction is crucial for grasping the braking dynamics involved.