Physics and Physiology Define the Hammer Throw

hammerthrowThe Hammer Throw is a Track and Field event which involves throwing a 12-16 pound ball secured on the end of a ~ 3.5 ft wire. Angles, trajectories, and even a unique physiological approach make this sport a precise and complex skill.

Learn the basics of how physics and physiology define the hammer throw.

Articles by Dave Kieda

Achieving the Perfect 10: Speed, Velocity, and Torque in Gymnastics

Utah Women's Gymnastics vs Stanford, January 28, 2011The vault, as with other gymnastics events, calls for an athlete to be in the best physical shape possible. Gymnasts need power in their legs, arms, and core, and must possess a huge mental capacity to focus on completing the right moves at the right time.  Other key factors involved in pulling off the perfect vault include agility and flexibility. A gymnast must strive to be in the top physical and mental shape in all of these areas if they hope to score the coveted perfect 10! But it takes elements of physics to ensure they can attempt the trick.

Learn the basics of how physics defines the vault.

Article by Kenny Morley

Physics and Physiology Define the Hammer Throw (Basic)

The Hammer Throw is a Track and Field event which involves throwing a 12-16 lb ball secured on the end of a ~ 3.5 ft wire. The other end of the wire is secured to a handle which is used to grip the hammer as it is thrown. The hammer is thrown by gripping the handle and swinging the hammer in a circle, then spinning one’s entire body for 3-4 turns and then the handle is released. A men’s championship collegiate hammer thrower will toss a 16 lb hammer 190 ft or more; the current world record distance (2011) is approximately 285 ft.

A primary concept associated with the hammer (as well as the shot-put) is the ballistic trajectory of the object, used to determine the optimal angle to release the device. The optimal  angle is almost independent of the speed of the steel ball when the hammer is released. In a vacuum, the optimal release angle  (angle between the velocity at release and the horizontal plane) for maximum distance would be 45°, but the presence of air resistance slows the horizontal velocity of the ball down, making the optimal release angle closer to 42-43°.

Achieving the proper release angle requires some thought and planning. When the hammer thrower begins the first turn, the plane of the hammer swing is considerably lower than 45°, closer to 10°. At the start of the throw, the velocity of the hammer in the ‘orbit’, combined with the radial distance from the thrower to the steel ball, defines the angular momentum of the hammer.  As the hammer thrower uses his legs to turn and accelerate the ball, he applies an off-axis torque to the angular momentum, and rapidly turns the orbital plane to steeper and steeper angles, achieving the optimal release angle near 42° in the final turn.

Since most hammer throwers will learn to throw near the optimal release angle fairly easily, the most important factor affecting the final travel distance of the hammer is the speed of the steel ball upon release. Because the hammer thrower uses a circular orbit to throw the hammer, the hammer thrower must exert a centripetal force to keep the steel ball moving on the circular orbit. This force is proportional to the square of the velocity of the hammer divided by the radial distance between the steel ball and the hammer thrower’s body (center of mass), and can easily reach 600lbs or more at release. The ability of the hammer thrower to withstand such huge force is the main limitation in the distance that can be thrown; most hammer thrower perform heavy weight lifting exercises in order to increase their ability to withstand this extraordinary force.

Having developed one’s strength to the maximum feasible, the hammer thrower has additional strategies for increasing the final velocity of the hammer while exerting the same centripetal force.  Since the centripetal force depends upon the square of the hammer velocity divided by the radial distance between the steel ball and the hammer thrower’s center of mass, higher velocities can be accommodated (with the same centripetal force ) by increasing that radial distance. Physiologically, this requires allowing one’s arms to extend as far our as possible, so championship class hammer throwers are generally tall, with exceptionally long arms. A particular individual, with a given arm length, can also increase the radial distance by working to keep the steel wire exactly perpendicular to one’s chest throughout the entire throwing motion. In addition, the hammer thrower will substantially increase the  orbit radius by completely relaxing the upper body and arms, allowing  the arms to dangle completely freely and relaxed as they carry the centripetal force.

At the same time the lower body and legs will drive as explosively as possible in order to accelerate the steel ball as quickly as possible to the final speed. The optimal technique for the maximum hammer throw distance is therefore “schizophrenic”: the upper half of the body is completely relaxed and passive, and the lower half of the body is completely energized with explosive power. This seemingly contradictory combination is what makes the hammer throw one of the most unique and spectacular events in track and field!

By: Dave Kieda, Department of Physics and Astronomy, University of Utah

Gloves and Geckos: How Football Gloves Echo the Gecko (Basic)

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

Learn more about the technical aspects of adhesion and polymers.

References:

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

Gloves and Geckos: How Football Gloves Echo the Gecko (Technical)

Figure 1

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!

Figure 2

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

References:

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.

 

From Tee to Fairway: How Physics Affects the Drive, the Club, and the Golf Ball

Golf Ball Velocity

Golf Ball Velocity

The average golfer drives the golf ball with an initial velocity of over 100 miles per hour.  If the player uses a club with a flexible shaft, the act of swinging adds an additional measure of torque as the head of the club also propels forward to connect with the ball.  The head of the club has grooves that increase the friction between the club and the ball, allowing the club to more effectively focus the area of contact.

The optimal angle to hit the ball ranges from about 12 to 20 degrees.  Putting a backspin on the ball increases lift and can add significant distance to the drive.  The dimples on the golf ball itself help reduce drag from the air stream by reducing turbulent air pressure around and behind the ball, shifting the wake further behind the ball, thus allowing for smoother, less resistant flight.   Any combination of these variables contributes to how well the ball overcomes the forces of gravity and air resistance.

Learn the basics of how physics affects golf or read the more technical details here.

Articles by Trevor Stoddard

From Tee to Fairway: The Basics of How Physics Affects the Drive, the Club, and the Golf Ball (Basic)

The motion of a golf ball can be thought of as a projectile, whose trajectory is parabolic and acted upon by gravity.  The initial velocity imparted to the ball by the club head can be broken down into both a horizontal and vertical component.  Numerous scientific studies have identified the optimum launch angle as 11-20° to achieve maximum distance (Erlichson, 1983). Though drivers are typically 8-10° in loft, the flexibility of the graphite driver shafts increases the launch angle through a split second whipping action (Zumerchik, 1997).  Golf clubs have grooves added to their faces to add some friction to the club head, so that momentum is transferred to the ball and backspin is created to generate lift. The difference between a ball with backspin and one without can add up to 100 yards after 2 or 3 seconds of additional flight time (Zumerchik, 1997).

There are several forces that act upon the aerodynamics of a golf ball in flight.  The most recognizable force acting upon a golf ball is gravity, which pulls the ball downward and creates the parabolic trajectory common of projectiles.  Another force on a golf ball is lift, the force that opposes gravity.  When backspin is transferred to the ball from the grooves on the clubhead, the velocity of air on top of the ball (which is moving in the direction of the backspin) is higher than the velocity of air on the bottom of the ball.  To counteract this, the Magnus effect generates lift on the ball and pushes it up.

In addition to gravity and lift, another force acting on a golf ball is drag, or air resistance.  As a golf ball is sent flying through the air, the molecules that come into contact with the front of the ball exert a large pressure force on the front of the ball (drag). Drag slows down the forward velocity of the ball. As the air comes into contact with the front of the golf ball, the fluid motion of the air becomes turbulent.  Turbulent flow can be thought of as smoke from a smoke stack- chaotic and wispy. As the turbulent air swirls around the golf ball, the dimples capture some of the swirls and keep them close to the surface of the golf ball. This means that the boundary layer of air stays close and hugs the ball longer, which means that there is a smaller pressure difference between the front of the ball and the back (when compared to a ball without dimples). The dimples thus allow the golf ball to travel farther than a smooth ball because the golf ball experiences less drag.

By: Trevor Stoddard, University of Utah

Learn more about the technical science behind golf.

References:

Benson, T. (2010) Drag of a Sphere.  National Aeronautics and Space Administration, Date Accessed:  8/10/2012 <http://www.grc.nasa.gov/WWW/k-12/airplane/dragsphere.html>

Bird, R. B., W.E. Stewart and E.N. Lightfoot. 2007. Transport Phenomena, 2nd edition, Wiley & Sons, New York.

Cochran, A. (ed.). 1990. Science and Golf.  New York: Chapman and Hall

Cochran, A. (ed.). 1992. Science and Golf II.  New York: Chapman and Hall

Davies, J.  1949. “The Aerodynamics of Golf Balls.”  Journal of Applied Physics 20: 821-828

Erlichson, H. 1983. “Maximum Projectile Range with Drag and Lift, with Particular Application to Golf.”  American Journal of Physics 51: 357-362.

Jorgensen, T. 1994. The Physics of Golf. New York:  American Institute of Physics

McDonald, W. 1991. “The Physics of the Drive in Golf.”  American  Journal of Physics 59: 213-218

Werner, F. and R. Greig. 2000. How Golf Clubs Work and How to Optimize Their Designs.  Jackson Hole, WY:  Origin Inc.

Wesson, J. 2009. Science of Golf.  New York, Oxford University Press

Williams, D. 1959. “Drag Forces on a Golf Ball in Flight and Its Practical Significance.”  Quarterly Journal of Mechanical Applications of Mathematics XII 3: 387-393

Zumerchik. J. (ed.). 1997. Encyclopedia of Sports Science.

Zumerchik J. 2002. Newton on the tee- a good walk through the science of Golf

History of the golf ball <http://www.golfeurope.com/almanac/history/golf_ball.htm> last accessed 8/10/12

95 miles per hour: Physiology of Pitching (Basic)

Major League pitchers throw the ball extremely hard, some at over 100 miles per hour.  Yet, as much as can be attributed to natural ability, much more can be attributed to strength, technique, and subtle keys revealed by modern science.

A muscle is composed mainly of proteins, with the addition of a few specialized organelles (Plowman and Smith 2008). What most people consider to be one muscle is actually millions of tiny filaments called myofibrils (Plowman and Smith 2008). Within these fibers, proteins and elements work together to create a muscle contraction.  As the requirement for force increases, more and more myofibrils are recruited to carry out the task.

In pitching, there are two important stages to the throw: the acceleration and deceleration phases.  Essentially, the acceleration phase starts when the arm comes forward and ends as the ball is released. The deceleration phases happens right after the ball is released and is where the body is trying to slow down the arm to prevent injury.  Studies have shown that the upper arms contribute to both acceleration and deceleration, as do the shoulders.  The chest and back both play an important role creating velocity (Jobe et al. 1983, Jobe et al. 1984, Escamilla and Andrews 2009). Although the literature is sparse, the core and lower body are thought to contribute a majority of the power during the throw (MacWilliams et al. 1998, Coleman 2009, Lehman 2012).

Since recent studies have alluded to the core and legs being integral parts of the throw, they become the focus of improving velocity.  Not only should the entire core be trained, but also all the muscles in the lower part of the body. In fact, a soon-to-be published study indicates that lateral jumps similar to the movement a pitcher makes are the most effective method to improving throwing velocity among common exercises (Lehman 2012).

The body requires more than just strong muscles to work. A high-performance body results from a combination of good nutrition and hours in the weight room and on the practice field.  Although not everyone can throw as hard as major league pitchers, everyone can improve their ability from where they are today. By applying basic scientific principles and putting in a little hard work, anyone can excel to rise among the ranks in whatever league they find themselves in.

Check out the technical physiology involved in pitching. 

By: Josh Silvernagel, Graduate Student, Bioengineering, University of Utah
Josh Silvernagel received undergraduate degrees in Exercise Science and Mathematics from Bemidji State University (BSU) in Bemidji, MN.  During his undergraduate studies, he was a four year starter in baseball for the BSU Beavers, where he both pitched and played infield.  In addition to providing sport specific training for ametuer and professional athletes following school, Josh spent two years coaching the sport at both the collegiate and high school levels.  He is currently working on a Ph. D. in Bioengineering at the University of Utah, where he studies cardiac electrophysiology in the CARMA Center.  Josh and his wife, Danielle, are recently married.

 

References

Coleman, A.E. 2009. Training the power pitcher. Strength and Conditioning Journal 31: 48–58.

Escamilla, R.F. and J.R. Andrews. 2009. Shoulder muscle recruitment patterns and related biomechanics during upper extremity sports. Sports medicine (Auckland, N.Z.) 39: 569–90.

Jobe, F.W., D.R. Moynes, J.E. Tibone, and J. Perry. 1984. An EMG analysis of the shoulder in a second report * pitching. American Journal of Sports Medicine 12: 218–220.

Jobe, F.W., J.E. Tibone, J. Perry, and D. Moynes. 1983. An EMG analysis of the shoulder in and pitching throwing preliminary report *. American Journal of Sports Medicine 11: 3–5.

Lehman, G., E.J. Drinkwater, and D.G. Behm. 2012. Correlation of throwing velocity to the results of lower body field tests in male college baseball Players. Journal of Strength and Conditioning Research / National Strength and Conditioning Association 3979.

MacWilliams, B., T. Choi, M.K. Perezous, E.Y. Chao, and E.G. McFarland. 1998. Characteristic ground-reaction forces in baseball pitching. The American Journal of Sports Medicine 26: 66–71.

Plowman, S. and D. Smith. 2008. Exercise physiology for health, fitness, and performance. Kippincott Williams and Wilkins, Philadelphia, PA, USA.

How Air Resistance Determines the Pitch (Basic)

To pitch a the highest level, a pitcher needs strength, flexibility, and intense focus.

When the ball is finally released, several forces act on it. First is gravity. The moment the ball leaves the pitchers hand, gravity begins to make the ball drop toward Earth. Gravity is basically the pull that an object of mass has on another object. Everything on Earth is affected by gravity. For example, a pencil you are using to take a math test has a pull on you and you have a pull on it! The only difference is that you have more mass than the pencil so you cannot feel the effects. The same is true for a baseball.Earth has an effect on the ball but also the ball has an effect on the Earth. However, the force of the ball on the Earth is not seen because of the tremendous difference in mass.

Another force that acts on the ball is air resistance. Air acts just like water! The only difference is that air is much less dense than water. This means that the microscopic air particles are much farther apart than the particles in water.  In a swimming pool, it is much harder to walk than when on land. This is because the water is providing a resistance against your body. Air provides a resistance as well but it is not felt as much because of the density differences. However, since a baseball is much lighter than you, air plays more of a role on a ball than on your body. The ball essentially must move air out of the way and this slows it down.  Imagine a skydiver opening up his parachute and falling slowly to Earth. This is exactly what happens to a baseball but on a much smaller scale.
Air resistance is also responsible for a pitcher being able to throw different kinds of pitches! When a pitcher throws a fastball, he throws it in such a manner that the spin is straight up. This will keep the ball going straight. When the pitcher throws a curve ball, he will tilt the spin so that the air resistance will push the ball in different directions (usually down or to the sides). In the case of a knuckleball, a pitcher will try to put zero spin on the ball. This will allow the air to push the ball in all sorts of directions and it appears to hitters that the ball is “dancing” through the air. This makes the pitch very deceptive and can lead to more strikeouts.

By: Kenny Morley, Ohio State University 

 

References:

Zarda, B. (2008, August 06). Science of a pitching freak. Retrieved from http://www.popsci.com/score/article/2008-08/science-pitching-freak

Free fall and air resistance. (2012). Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l3e.cfm