The football is following a trajectory. The spin enables it to follow the trajectory like a shell from a cannon. When a shell is fired it begins and ends the trajectory always pointing forward.
I understand the trajectory OK but that would be true for a smooth bore cannon ball as well as an artillary shell. But if the cannon were fired upward at 45º shouldn't the spin continue to hold the shell at 45º wrt the earth during its entire flight? What force would cause the shell to go from an upward 45 º to a downwrd 45º. That is the part I don't understand. If a force were exerted on the shell (or football), shouldn't the precession cause the shell to turn to the left or right depending on the direction of spin?
I'm sorry that I can't comment on yourcomment but just keep in mind that for the shell to explode on target it must hit the target with ts nose.
