That is, the acceleration is constant at the beginning.

The force analysis of the car shows that F-f=ma. Because the acceleration is constant and the sliding friction is constant, the traction force increases at a uniform speed. And v=at, P=Fv, the power also increases linearly.

But when the speed reaches a certain level, that is,

Fv=P amount

When the power cannot be increased, the traction will decrease, the speed will still increase and the image will be bent. Finally, when F=f, the image is flat.

Overall: first straight, then curved, and finally flat.

★ Start at rated power:

Start with constant power.

Because P=Fv, p remains unchanged and v increases, so f must decrease. So the whole image is curved from the beginning, and finally flattens when f = f

The above is the law I summarized, please refer to it.