Every year Chicago dyes part of its river green to celebrate St. Patrick’s Day. This timelapse video gives a great view of the 2016 dyeing. If you watch closely, you’ll see that what’s being put in the river isn’t originally green. It’s actually an orange powder being distributed through flour sifters by the men on the boat. The exact formula is secret, but the dye is considered environmentally safe. To mix up the dye, a chase boat follows the dye boat, using its motor and wake structure to help add some turbulence to the river. It takes several passes to get the water uniformly green, but it requires a remarkably small amount of dye to do so, only about a paint can’s worth. So enjoy a little fluid dynamics today with your festivities! (Or, if you prefer to celebrate a different sort of fluid dynamics today, allow me to offer you the physics of Guinness.) (Video credit: Chris B Photo)
Tag: st patricks day
Greening the River
Every year Chicago dyes its river green in honor of St. Patrick’s Day. This timelapse video shows this year’s dyeing, including several passes from a boat distributing the green dye. The color is remarkably slow to diffuse. The boat’s passage does little to affect the motion of the dye already in the river. This is because the boat mainly disturbs the surface and most of the color comes from dye spread throughout the water. It’s like if you tried to stir milk into your coffee just by tapping the surface with your spoon. Instead, the slower, large-scale turbulent motion of the river distributes the dye. For more St. Patrick’s Day physics, be sure to check out Guinness physics and why tapping a beer makes it foam. (Video credit: P. Tsai; submitted by Bobby E.)