This is an excerpt from an elementary Physics textbook ("Fundamentals of Physics" by Halliday), which describes what happens when a wheel that is "rolling without slippging" doesn't have a constant speed. This part doesn't make sense:
Figure 11-7 shows an example in which a wheel is being made to rotate faster while rolling to the right along a flat surface, as on a bicycle at the start of a race. The faster rotation tends to make the bottom of the wheel slide to the left at point P. A frictional force at P, directed to the right, opposes this tendency to slide.
Why does this frictional force go the same direction as the force that's accelerating the wheel? I've seen some numerical proofs of this on StackExchange, but I couldn't find a conceptual proof for it.