Dear Dr. Universe,
How do parachutes work?
— Lucas, 11, Alberta, Canada
Have you ever blown on a puffy white dandelion? Your breath sends dozens of seeds scattering, gliding to a soft landing somewhere new.
Look closely at one of those seeds, and you’ll see a familiar shape. The tiny passenger (the seed) has a wispy, circular top, which helps it float to its next destination.
Parachutes work a lot like dandelion seeds — using the same invisible forces all around us. Nicholas Cerruti, a physics professor at Washington State University, helped me learn how.
The air around you is packed with tiny things called molecules. You can’t see them, but you’re constantly bumping into them. This is true for you, and for every object in motion on Earth.
“As an object moves through air, it needs to move the air around it,” Cerruti explained.
Imagine you drop a piece of paper. As the paper falls, it strikes air molecules. Molecules bounce off the paper and each other. Bumping together, they produce a force. As the paper falls, air molecules push against it in the opposite direction. This force slows the paper’s motion.
Scientists call this “air resistance” or “drag.” Gravity pulls everything down on Earth: whether it’s a person jumping from a plane or a paper falling from your hand. But drag works against that pull, slowing it down.
Some objects fall faster than others because they produce less drag. “A classic example is a penny and feather,” Cerruti said. “If you drop a penny and feather at the same time, the feather will drop at a slower rate.”
A feather takes up more space than a penny, just like a person takes up more space with a parachute. With more surface to work against, the air gives a bigger push against gravity’s pull. That’s why someone with a parachute falls more slowly than someone without one.
Parachutes work by creating lots of drag. The same idea appears in nature: in dandelion seeds, bird wings, and more. “Flying squirrels have a skin between their legs that develops like a parachute,” Cerutti said. “Instead of the squirrel dropping out of a tree, they can glide.”
Every year, Cerruti and the Physics and Astronomy Club test these ideas by dropping pumpkins from the top of a tall building.
“Usually we use parachutes on pumpkins as a joke,” he said. “We’ll put a very small parachute on, and it doesn’t slow it down very much. But we’ve been doing an egg drop the past couple of years. Using parachutes really does slow down the egg, and it can land safely.”
You can try this out yourself at home. Ask an adult to help you find a coffee filter or plastic bag and some string.
Try attaching your “parachute” to different small objects: an action figure, pencil, or penny.When you drop them, do they slow down? Can you help your passenger fall to a soft landing? Try it and see what works!
Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu.