>>64435938
>>64435942
>>64436090
>horse archery
>stirrups

Irrelevant like the other anon said. Stirrups are for bracing yourself against the horse so you can exert more force via a handheld object.

>Force = Mass x Acceleration

Acceleration is the combined speed of your horse and your swinging arm, your mass is you own, but stirrups allow you to add ~1000lbs of horse ass to the force of your swing.