The moment of f is equal to the moment of gravity, and the change of gravity is the same as that of gravity arm.

The rod has no mass, and the actual mass is concentrated in the center of the disk, which is connected with the fulcrum. When pulling, the gravity of the disc is constant, and the maximum force arm is the length of the connecting line between the center of the disc and the fulcrum, so the torque increases first and then decreases.

As shown above, it is balanced by moment:

GL 1cosβcos(α？ β)=F？ L2cosα？ Get: F=GL 1cosβL2cos(α？ β)× 1 cosα= GL 1 cosβL2(sinα+tanαcosβ)

In the above formula, the only variable is tanα. When α changes from 0 to 90, its value is increasing function, so the pulling force F always increases.

So the situation is: increase first and then decrease, and keep increasing.