How powerful is a sling?

I'm curious to know, just how powerful can a sling truly be? Is it a mere tool for children's games, or does it possess the capability to inflict serious damage? Have there been any historical instances where a sling has been used effectively in battle, showcasing its strength and potential? And if so, what factors contribute to the power of a sling, such as the material used, the size and weight of the projectile, or the skill of the user? I'm eager to gain a deeper understanding of this ancient weapon and its capabilities.