Learn the basics of punting.
Articles by Kenny Morley
Articles by Kenny Morley
In football, players use gloves as a means to help control the ball, particularly when making catches. In order to develop better gloves, an understanding of how materials actually adhere (stick) to each other is required. Scientists are constantly searching for new and innovative ideas for adhesive substances. Often, new substances are modeled after examples found in nature. In 2008, a group of scientists developed an adhesive material modeled after the foot pads of the gecko.
Articles by Bret Van Ausdall
In sports, one of the most important forces is friction. In football, players have started to use gloves as a means to help control the ball better, particularly with making catches. Companies such as Nike, Cutter, Reebok, and Adidas all market gloves that have higher and higher levels of ‘tack’, a term used for how well the gloves can grip things. In order to develop better gloves, an understanding of how things actually adhere (stick) to each other is required. This is a concept that scientists have been studying for a long time, making better and better glues. Now, scientists and companies are focused on making better ‘dry adhesives’ that can go on gloves, tapes, or anything where an adhesive might find use. Scientists examine the molecular basis of adhesion using various methods, including Atomic Force Microscopy, to explore new substances and identify possible adhesive materials for use with sports applications.
Looking for inspiration, scientists have turned to nature and examined the gecko to see how it can stick to glass walls and run up rock faces with such ease. In this research, scientists have determined that geckos use uniquely structured keratin setae pads to stick to and release from slippery surfaces (Qu 2008). This research has prompted chemists to develop a non-biological material that has a very similar structure to the gecko’s own pad.
Football gloves have come a long way, from the use and ban of the axle grease-like substance Stickum, to the purported use of neoprene scuba gloves, and to the gloves players use today. In time, it may be possible that some of the newest discoveries in adhesive materials – such as the material inspired by the gecko – will find their way into the sports arena.
By: Bret Van Ausdall, University of Utah
Qu, L., L. Dai, M. Stone, Z. Xia, & Z.L.Wang. 2008. Carbon nanotube arrays with strong shear binding-on and easy normal lifting-off. Science 322:238
How can a gecko affect a football game? “By selling car insurance on commercials during halftime?” would be the wrong answer. Rather, instead of watching a gecko sell insurance, one would have to look carefully at a gecko hanging off the glass walls of its aquarium, much like a reptilian Spider-man, to see that football pros could learn a lot from geckos. This is exactly what researchers at the University of Dayton and Georgia Technical Institute have done (Qu et al. 2008). Researchers garnered inspiration from a paper published in Nature (Autumn et al. 2000) which examined the pad of a gecko to determine exactly how it is able to stick so effortlessly to something as slippery as glass. They then applied the sticky gecko pad concept as they created a carbon nanotube array on a small piece of silica. What researchers over the years have been able to determine is that a gecko’s foot can have upwards of 500,000 seta, which are small fibers that are composed of keratin with spatula-shaped portions at the end (see figures 1 and 2)
Keratin, a polymeric protein comprised of several units of various forms of keratin monomers, is the same material found in our hair and skin, though gecko’s cells align the keratin in a different fashion than our bodies. Mammals produce a form of keratin called alpha-keratin that has within it lots of alpha-helices (Huggins 1957), basically columns that stack together (Huggins 1977), that are found in our skin, fingernails, hair, and elsewhere in our bodies (Moll et al. 2008). Geckos, and reptiles in general, produce and assemble keratin together in a form called beta-keratin, which contains within it repeating beta-pleated sheets instead of alpha helices (Maderson 1964). The geckos with their beta-keratin also have the extra feature of these strong, rigid setae on their pads, which enable them to perform their miraculous wall-climbing feats. Researchers have determined the pad of a gecko can support up to 10 Newtons per cm2 (N cm-2) (Irschick et al. 1996); however, the carbon nanotube silica pad produced by the Dayton and Georgia Tech researchers produced 100 N cm-2! In other words, if the same gecko weighed 10 times as much, it would still be able to hang from the glass wall safely if it had the silica and carbon nanotubes on its pad!
So, one asks, how can this relate to football? How can the pad of a gecko provide an advantage to improve my favorite high school/college/NFL team’s chances at winning? Notice the gloves some of the players wear. These gloves, as one would find out quickly after wearing a pair, amplify the grip of the athlete on the football, allowing them to make even more amazing and athletic catches. The underlying concept of these gloves revolves around the material covering the fingers of the glove, which has a higher coefficient of friction to the material of the football than skin does. Basically, this means that the material on the glove ‘sticks’ to the football better than your skin. Cutters, a leading manufacturer of football receivers’ gloves, has data showing that their gloves have some of the most ‘tack’ in the field (Basic Guide to van der Waals forces 2012).
How do any of the materials, be it silica and carbon nanotubes, or material found on the football players’ gloves, work? It’s a similar question one might ask when playing with super glue: how does glue stick two different materials together? This is a question that has been posed for some time and was even addressed at the First International Congress on Adhesion Science and Technology in 1996 (Somorjai 1998). Generally speaking, adhesion can be divided into two classes: Strong adhesion and Weak adhesion. Strong adhesion deals with the strong chemical bonds of an adhesive to a material, where the adhesive’s interactions are ordering on the magnitude of, or at times stronger than, the bonds within the material the adhesive is sticking to. Weak adhesion deals primarily with van der Waals force, and it is thought that the setae on the gecko’s pads operate using these forces. Van der Waals forces are a form of weak intermolecular interactions with which molecules and atoms can interact with each other (Basic Guide to van der Waals forces 2012). Though van der Waal forces may be weaker than actual chemical bonds between atoms, if there are enough molecules present, for example on the pad of a gecko, the interactions generated between the pad of a gecko and a glass wall can be quite large.
The various strengths of intermolecular forces and interactions at the molecular level lead to the concepts of friction, lubrication, and adhesion. The concept of adhesion has industrial applications (such as motor oil as a lubricant in an engine and ‘tacky’ gloves for athletes), but in order to test the ‘adhesiveness’ of a substance, scientists must have methods to test a substance’s properties. One method used to test the ‘adhesiveness’ of a substance is atomic force microscopy (“AFM”).
AFM is conducted by using an extremely small pin, approximately one atom wide, attached to a lever. As the pin is lowered towards a surface to be tested and moved around the surface of the material, the tip starts to move in response to the molecules at the surface of the substance. The movements of the lever are recorded. When the interactions are compared to other materials, it provides insight into how the properties of different materials compare. The types of forces a pin tip can experience are chemical bonding, magnetic forces, electrostatic forces, and van der Waals forces, among others (Lang et al). A similar technique, scanning force microscopy, was invented by Gerd Binnig and Heinrich Rohrer in the 1980’s, but led to the discovery of AFM. The extreme utility of these techniques led to Binnig and Rohrer winning a Nobel Prize in Physics in 1986. Researchers all over the world have used AFM and variations of it to examine various types of materials and test them for their adhesive forces (Thomas et al. 1995) as well as to examine molecular origins of friction.
When companies start to design products like receivers’ gloves, they are not just going out and using AFM to find the stickiest substance around. A material known as Stickum, produced by Mueller Sports Medicine, was used by Lester Hayes in the NFL in the 1970’s. His liberal use of the material prompted a ban on the substance. Stickum itself has been redesigned from the original gooey, stick-to-everything substance to a new powder that is sprayable. Companies and researchers are still perfecting the ‘dry’ adhesive technologies, going from leather gloves, leather gloves treated with tackifying resins, and leather gloves treated with a silicon resin to enhance frictional forces (Kang 2002). Regardless of how, science has helped make football more competitive and exciting by providing highly advanced polymer coated gloves that, when coupled with some of the most athletic people in the world, enable breath-taking, one-handed, catches.
By: Bret Van Ausdall, University of Utah
Autumn, K., Y.A. Liang, S.T. Hsieh, W. Zesch, W.P. Chan, T. W. Kenny, R. Fearing, and R.J. Full. 2000. Adhesive force of a single gecko foot-hair. Nature 405:681.
Basic Guide to van der Waals forces. 2012. Retrieved from http://www.chemguide.co.uk/atoms/bonding/vdw.html#top
Cutter Fall Catalogue. 2012. Retrieved from http://www.cuttersgloves.com/catalog_fall12/
Huggins, M. L. 1957. The structure of alpha keratin. Proceedings of the National Academy of Sciences of the United States of America 43:204.
Huggins, M. L. 1977. The Structure of α-Keratin. Macromolecules 10:893.
Irschick, D. J., C.C. Austin, K. Petren, R.N. Fisher, J.B. Losos, and O. Ellers. 1996. A comparative analysis of clinging ability among pad-bearing lizards. Biological Journal of the Linnean Society 59:21.
Kang, H. S. “Athletic glove having silicone-printed surface for consistent gripping ability in various moisture conditions.” Patent 6,408,442. 25 June 2002.
Lang, K. M., D. Hite, R.W. Simmonds, R. McDermott, D.P. Pappas, and J. Martinis. 2004. Conducting atomic force microscopy for nanoscale tunnel barrier characterization. Review of Scientific Instruments. 75:2726.
Maderson, P. 1964. Keratinized epidermal derivatives as an aid to climbing in gekkonid lizards. Nature 203:780.
Moll, R., M. Divo, and L. Langbein. 2008. The human keratins: biology and pathology. Histochemistry and Cell Biology 129:705.
Qu, L., L. Dai, M. Stone, Z. Xia, and Z.L.Wang. 2008. Carbon nanotube arrays with strong shear binding-on and easy normal lifting-off. Science 322:238
Somorjai, G. A. 1998. The molecular surface science of adhesion. Pages 3-15 in W.J. van Ooij and H.R. Anderson, Jr., editors. First International Congress on Adhesion Science and Technology. Ridderprint bv, Ridderkerk, The Netherlands.
Thomas, R. C., J.E. Houston, R.M. Crooks, T. Kim, and T.A. Michalske. 1995. Probing adhesion forces at the molecular scale. Journal of the American Chemical Society 117:3830.
Before the punter is able to punt the ball, there are several other elements he needs. First…the ball. One interesting fact about kickers is that they get their own balls inscribed with a K that is used in the game only for kicking. NFL Footballs are filled to between 11 and 13 psi but the special kicking balls are always filled to the highest possible pressure of 13 psi. PSI stands for pounds per square inch and this literally means that there is between 11 and 13 pounds of pressure pushing on each square inch of the football. When the air pressure is increased, the elasticity also increases. Elasticity is essentially how well the football is able to release energy and convert it into movement. With high pressure in the ball, the gases that expand when the ball is kicked are able to transfer energy to motion much easier than if their was less air pressure. Kickers have also been known to be very protective of their footballs. They rub them down with a horsehair brush and this removes the film and shows the stickier surface. This allows a punter to hold on to the snap much easier. The horsehair brush also firms up the ball and this increases the elasticity of the ball even further.
Finally, the punter is ready to step onto the field and do what he does best: punt the ball. Before the snap, a punter typically stands around 14 yards behind the ball. The first important part of the punt is the snap. The long snapper needs to get the ball the 14 yards into the punters hands. To do this, he must spin the ball in a counter-clockwise motion and throw it through his legs with considerable force. This spinning, similar to a bullet coming out of a gun, makes the football fly much straighter and makes it easier for the punter to catch.
When the snap is received, the punter will take 2 steps and attempt to drop the ball level or with the nose of the ball tilted slightly up. It is essential to kick as much of the ball as possible so that more force is transferred from the punters foot into the ball. Dropping the ball straight down allows for the punter to get his foot on a large portion of the ball, but it also allows him to put spin on the ball. This spin not only makes the punt more accurate, but it also causes the ball to stay in the air longer (this is called “hang-time”).
When the ball is finally kicked it becomes a projectile and follows the rules of projectile motion. The angle of the ball, when it leaves the punters foot, is very important. The ideal angle for the longest kick would be 45 degrees but different game situations may call for a different angle. For example, if the punter wanted to kick the ball higher, he would use an angle greater than 45 degrees to achieve that height. The ball flies in a parabolic shape and its motion can be described using vectors. Vectors are lines that describe the velocity and the direction of an object in motion, which in this case is the football. A punted football has a vertical velocity vector as well as a horizontal velocity vector. The vertical vector describes how the football is moving up and down while the horizontal vector describes the motion relative to the ground. When the football is at its highest, the vertical velocity vector is 0 and this is where punters want the spin of the ball to help hold it in mid-air. The longer the ball is able to stay at this point, the higher the hang-time and the farther the ball will fly.
Some equations that will govern the flight of the football include:
Where V0 = initial velocity
Vy0 = initial vertical velocity
Vx0 = initial horizontal velocity
t = time
g = acceleration due to gravity
Θ = angle of the kick
By: Kenny Morley, Ohio State University
Freudenrich, C. (2012). How the physics of football works. Retrieved from http://www.howstuffworks.com/physics-of-football2.htm