Featured Research

from universities, journals, and other organizations

What's behind the success of the soccer 'knuckleball'

Date:
November 16, 2012
Source:
American Physical Society's Division of Fluid Dynamics
Summary:
What makes soccer star Christiano Ronaldo’s “knuckleball” shot so unpredictable and difficult to stop?

What makes soccer star Christiano Ronaldo's "knuckleball" shot so unpredictable and difficult to stop? At the American Physical Society's (APS) Division of Fluid Dynamics (DFD) meeting, November 18 -- 20, 2012, in San Diego, Calif., a team of researchers investigating this phenomenon will reveal their findings.

A "knuckleball" in soccer refers to a ball kicked at very low spin, which results in a zigzag trajectory. Along its straight path, the ball deviates laterally by roughly the diameter of a ball (0.2 m). The deviation direction appears to be unpredictable, which is extremely frustrating for goalkeepers attempting to block it.

Variations of the knuckleball are also used in baseball and volleyball, so many players and coaches want to understand the physics at play during its zigzag trajectory.

"We decided to study the knuckleball because the physics of sports is such a new field and there are many discoveries to be made," explains Caroline Cohen, a Ph.D. student at Ιcole Polytechnique's Hydrodynamics Laboratory (LadHyX) in France.

After trying other experiments, Cohen and colleague Baptiste Darbois Texier, also a Ph.D. student, working with Christophe Clanet, a research director at France's Centre National de la Recherche Scientifique (CNRS), focused on an approach that involves dropping steel beads into a tank of water and studying their trajectory. They discovered that the knuckleball phenomenon occurs, but at much shorter distances. This makes it easier to observe with an ultrafast camera, which lets you see things you can't with the "naked" eye.

"The big surprise is that every bead makes a zigzag -- from a little plastic bead to a steel weight of 7 kg (15.4 lbs)," says Cohen. "We wouldn't have bet on this occurring before we tried it, so it was quite exciting to actually see it by doing a simple experiment."

The team demonstrated that -- contrary to popular belief -- the "knuckle effect" isn't a result of deformations at the site of foot impact or ball seams. What's really going on is that the aerodynamic lift forces that act on a smooth sphere can fluctuate and cause the zigzagging.

At the DFD meeting, Darbois Texier will also describe the significant role the knuckle effect may have played in historic experiments trying to prove Earth's rotation. "One way to attempt this is to measure the East deviation of a sphere in free fall -- from a height of 150 m (492 ft) the deviation is about 3 cm (1.18 in)," he notes. "We found that the results of these experiments were very scattered, and we believe this is because of the lateral deviation caused by the knuckle effect."


Story Source:

The above story is based on materials provided by American Physical Society's Division of Fluid Dynamics. Note: Materials may be edited for content and length.


Cite This Page:

American Physical Society's Division of Fluid Dynamics. "What's behind the success of the soccer 'knuckleball'." ScienceDaily. ScienceDaily, 16 November 2012. <www.sciencedaily.com/releases/2012/11/121116085201.htm>.
American Physical Society's Division of Fluid Dynamics. (2012, November 16). What's behind the success of the soccer 'knuckleball'. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2012/11/121116085201.htm
American Physical Society's Division of Fluid Dynamics. "What's behind the success of the soccer 'knuckleball'." ScienceDaily. www.sciencedaily.com/releases/2012/11/121116085201.htm (accessed October 21, 2014).

Share This



More Matter & Energy News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Thanks, Marty McFly! Hoverboards Could Be Coming In 2015

Newsy (Oct. 21, 2014) — If you've ever watched "Back to the Future Part II" and wanted to get your hands on a hoverboard, well, you might soon be in luck. Video provided by Newsy
Powered by NewsLook.com
Robots to Fly Planes Where Humans Can't

Robots to Fly Planes Where Humans Can't

Reuters - Innovations Video Online (Oct. 21, 2014) — Researchers in South Korea are developing a robotic pilot that could potentially replace humans in the cockpit. Unlike drones and autopilot programs which are configured for specific aircraft, the robots' humanoid design will allow it to fly any type of plane with no additional sensors. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
Graphene Paint Offers Rust-Free Future

Graphene Paint Offers Rust-Free Future

Reuters - Innovations Video Online (Oct. 21, 2014) — British scientists have developed a prototype graphene paint that can make coatings which are resistant to liquids, gases, and chemicals. The team says the paint could have a variety of uses, from stopping ships rusting to keeping food fresher for longer. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
Portable Breathalyzer Gets You Home Safely

Portable Breathalyzer Gets You Home Safely

Buzz60 (Oct. 21, 2014) — Breeze, a portable breathalyzer, gets you home safely by instantly showing your blood alcohol content, and with one tap, lets you call an Uber, a cab or a friend from your contact list to pick you up. Sean Dowling (@SeanDowlingTV) has the details. 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