It’s extremely difficult to turn a penny into a lethal weapon. Even from the height of a skyscraper, a penny is too small and flat, and cushioned by too much air, to become a torpedo. Instead, it would flutter to the ground, like a leaf. If it did strike you, it would feel like being flicked in the forehead — “but not even very hard,” said Louis Bloomfield, a physicist at the University of Virginia.

Source – https://www.scientificamerican.com/article/could-a-penny-dropped-off/