When cycling, if you suddenly apply the front brake at a high speed, it's easy to experience a dangerous front flip. Why is this? It's all because of friction causing trouble.
There's a risk of flipping over when suddenly applying the front brake on a bicycle. When you brake the front brake of a bicycle, the front wheel is locked, and the friction between the front wheel and the ground changes from the static friction experienced during normal riding to sliding friction; the rear wheel still experiences rolling friction with the ground. Since the rolling friction is much smaller than the sliding friction, it can be ignored, meaning that the bicycle only considers the sliding friction experienced by the front wheel in the horizontal direction. Due to the inertia of the bicycle, it still moves forward at its original speed at the moment of braking. If we take the bicycle as the reference frame, the bicycle is subject to an inertial force acting in the same direction as its motion; with the front wheel as the fulcrum, the torque generated by the inertial force is equal to or greater than the torque of the gravity acting on the bicycle and the rider as a whole. At this point, the supporting force of the rear wheel on the ground becomes zero, meaning that the bicycle will tip over and lean forward as a whole. The faster you brake, the greater the inertial force will be, and the larger the torque generated by the inertial force will be, making it more likely for the bicycle to flip over.