In the subjects section on the title bar,there are 3 Physics course that can be followed. They are- Physics, AP Physics 1 and AP Physics 2.The Physics course includes all the topics that are discussed in both AP Physics 1 and 2.  I looked into them and found it confusing that there are less number of lectures per topic in AP Physics 1 & 2 than that of the Physics course. For example, the first topic in both Physics and AP Physics 1 is One-dimensional motion. In this case,AP Physics 1 has 37 lectures and Physics has 41 lectures. 

Can someone explain the reason of this? Moreover,I'm not sure which course I should start taking.