Featured Research

from universities, journals, and other organizations

Why Thin, Flat Things Rise And Glide On The Way Down: Cornell Physicists Finally Solve The Falling-paper Problem

Date:
October 20, 2004
Source:
Cornell University
Summary:
An enterprising professor and her graduate student at Cornell University have solved the falling paper problem -- in part by calculating the motions of a scientific journal page in flight.

The seemingly chaotic motions of this page from a scientific journal became part of a computer modeling exercise to show why flat things don't fall straight down. (J. Wang and U. Pensavento/Cornell University. Copyright Physical Review Letters 2004)

ITHACA, N.Y. -- Exactly what governs the motions of falling paper?

Related Articles


While college students suspect the answer is known to lazy professors -- the ones who allegedly grade essays by throwing them down stairwells to see which sails the farthest -- the so-called falling paper problem has long intrigued scientists.

Now an enterprising professor and her graduate student at Cornell University have solved the falling paper problem -- in part by calculating the motions of a scientific journal page in flight -- and their report must have made the grade: The journal Physical Review Letters (Vol. 93, No. 14, "Falling Paper: Navier-Stokes Solutions, Model of Fluid Forces, and Center of Mass Elevation") article by Z. Jane Wang, associate professor of theoretical and applied mechanics, and Umberto Pesavento, a Ph.D. candidate in physics, explains it all.

The same falling-paper principles apply, the physicists believe, to naturally flat things like leaves. If they are right, Wang and Pensavento may have finally solved the mystery of why autumn leaves depart from a neighbor's tree on a windless day . . .

. . . rise into the air . . . . . . rise again . . .

. . . glide along . . .

. . . and have to be raked from yards that don't contain a single tree.

As Wang explains, "Leaves and paper fall and rise in a seeming chaotic manner. As they fall, air swirls up around their edges, which makes them flutter and tumble. Because the flow changes dramatically around the sharp edges of leaves and paper, known as flow singularity, it makes the prediction of the falling trajectory a challenge."

Among the first scientists to be intrigued by the behavior of falling paper was Scottish physicist James C. Maxwell, who pondered the tumbling motions of playing cards in 1853. But while Maxwell was a brilliant mathematician, he lacked the today's computer-modeling techniques, not to mention access to fast, powerful computers. Wang and Pensavento put those advanced tools to good use to show why the falling trajectory of thin flat things -- and the behavior of airflow and other forces -- is not predicted by the classical aerodynamic theory.

"There were a few surprises," Wang notes. "We found the flat paper rises on its own as it falls, which would not happen if the force due to air is similar to that on an airfoil. Instead, the force depends strongly on the coupling between the rotating and translational motions of the object."

Wang and Pesavento also showed that the falling-paper effect is almost twice as effective for slowing an object's descent, compared with the parachute effect (that is, if an object falls straight down). And that evidently benefits trees and other plants that need to disperse seeds some distance from the point of origin. Plants with flattened seedpods also take advantage of the falling-paper effect.

The research was funded by National Science Foundation, the U.S. Air Force Office of Scientific Research and the Packard Foundation.

Says the professor who does not use the falling-paper effect to grade student essays and forecast their future: "What is predictable is that as the autumn leaves tumble down, they drift in particular directions, depending on the way they turn. This may explain, Wang adds, "why you are getting the leaves from your neighbor."


Story Source:

The above story is based on materials provided by Cornell University. Note: Materials may be edited for content and length.


Cite This Page:

Cornell University. "Why Thin, Flat Things Rise And Glide On The Way Down: Cornell Physicists Finally Solve The Falling-paper Problem." ScienceDaily. ScienceDaily, 20 October 2004. <www.sciencedaily.com/releases/2004/10/041020093646.htm>.
Cornell University. (2004, October 20). Why Thin, Flat Things Rise And Glide On The Way Down: Cornell Physicists Finally Solve The Falling-paper Problem. ScienceDaily. Retrieved November 23, 2014 from www.sciencedaily.com/releases/2004/10/041020093646.htm
Cornell University. "Why Thin, Flat Things Rise And Glide On The Way Down: Cornell Physicists Finally Solve The Falling-paper Problem." ScienceDaily. www.sciencedaily.com/releases/2004/10/041020093646.htm (accessed November 23, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Sunday, November 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

AFP (Nov. 21, 2014) Toyota presented its hydrogen fuel-cell compact car called "Mirai" to US consumers at the Los Angeles auto show. The car should go on sale in 2015 for around $60.000. It combines stored hydrogen with oxygen to generate its own power. Duration: 01:18 Video provided by AFP
Powered by NewsLook.com
Google Announces Improvements To Balloon-Borne Wi-Fi Project

Google Announces Improvements To Balloon-Borne Wi-Fi Project

Newsy (Nov. 21, 2014) In a blog post, Google said its balloons have traveled 3 million kilometers since the start of Project Loon. Video provided by Newsy
Powered by NewsLook.com
Raw: Paralyzed Marine Walks With Robotic Braces

Raw: Paralyzed Marine Walks With Robotic Braces

AP (Nov. 21, 2014) Marine Corps officials say a special operations officer left paralyzed by a sniper's bullet in Afghanistan walked using robotic leg braces in a ceremony to award him a Bronze Star. (Nov. 21) Video provided by AP
Powered by NewsLook.com
British 'Bio-Bus' Is Powered By Human Waste

British 'Bio-Bus' Is Powered By Human Waste

Buzz60 (Nov. 21, 2014) British company GENeco debuted what its calling the Bio-Bus, a bus fueled entirely by biomethane gas produced from food scraps and sewage. Jen Markham explains. Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins