Science in Soccer The game of soccer is one of the most popular sports participated in by people all around the world. People gather together to watch ninety minutes of exciting goals, dirty slide tackles, and beautiful ball movement. But, did you know that behind all of that lies the power of science? Physics in particular can be found in many aspects of soccer. When studying forces, one can recall Newton’s Laws of Motion. Newton’s second law states that an object that accelerates does not have a net force of zero. In the game of soccer, there are countless moments in which players ‘accelerate’ towards the ball; thus, in a physics perspective, the player’s net force is no longer zero but greater than zero. As well, Newton’s third law—that every force has an equal and opposite force acting upon it —is shown through the collisions between players, and through the forces between one’s feet and the ground whilst running. The ball itself is influenced by physics-related forces such as the force of gravity and the drag force. All of these concepts are found within the game of soccer; showing us the power of physics within our world.
Physics in Sports Equipment Physics is found not only through the movement and impact of the players or the ball, but through their sports equipment. Many instances in the game through which sports equipment come into play involve the concept of forces in physics. One of the most essential pieces of equipment in soccer are soccer cleats. In any pair of shoes, there must be a force that will enable you to move from one direction to another, without falling. In physics, this is called traction or the force of friction. Soccer cleats must be designed to have materials that will allow more friction to be present so that one will not slip and fall, and also so that one will be able to change direction rather quickly. There are many different soccer cleats that have been created with different designs; in this magazine, you will be given a glimpse of different designs and new combinations that will maximize a cleat’s usefulness for a soccer player in various conditions.
Soccer Cleats There are many different kinds of cleats that are used in different conditions today. The two main categories for materials in soccer cleats include: leather and synthetics.
In most cases, leather material cleats will absorb water quickly, making it very heavy and thus decreasing speed; whereas, synthetic materials do not absorb water quickly and so they allow you to retain your speed. Therefore, it is recommended that leather-material cleats are not worn in rainy conditions. Many of the leather cleats such as kangaroo leather are beneficial because they mould nicely into the shape of your foot; thus, when dry, they feel much lighter and are more comfortable. But, on the downside, they are less durable. Whereas, synthetic cleats are stiffer but are more durable. These two cleats contrast one another and depending on certain weather conditions, one kind can be chosen over another.
This chart shows what we will be mainly focusing on—the bottom part of soccer cleats, that provide friction. There are two kinds of bottoms: ones that are already molded onto the bottom of the shoe and ones that can be screwed in. The molded bottoms can come in two different shapes, rounded conical figures or ‘blades’ that are placed at different angles in order to stabilize the shoe. These studs are strategically placed in many different locations of the shoe so that the shoe is balanced and no greater force is exerted on one part of the foot in comparison to another—this would cause an injury. The difference between these two shaped studs is that the blades have a greater surface area, and a greater volume than the rounded studs. From studying forces, one will know that greater surface area means that a greater amount of the material will experience friction between the surface it is being placed upon. As well, the blades have a greater volume, thus increasing the total mass of the object. Again from forces, we know that the force of friction is found by multiplying the normal force and the coefficient of friction. The normal force in this equation is dependent on the mass of the object because it is found through the mass times the force of gravity. Therefore, a greater mass will result in a greater normal force; and thus, a greater amount of friction. From this, we can see that cleats with bladed studs on the bottom provide greater amounts of friction in comparison to rounded bottoms.
Soccer Cleats Depending on which surfaces you are playing on, you may want to choose rounded bottoms for firmer grounds that donâ€™t require a lot of friction; or, you may choose bladed bottoms for softer grounds that require much more friction. The material of the molded studs on the bottom of cleats is plastic. In contrast, for cleats with screw-in bottoms, both plastic and aluminum studs can be used; the only thing that stays constant is the shapeâ€”rounded. These cleats are very helpful in terms of variety or changes in conditions because instead of buying two different pairs of shoes, you can just unscrew the studs and change them for the appropriate studs needed. The new material found in this type of boot is the aluminum bottoms. Why would a shoe have both plastic and aluminum bottoms? Well, these two materials contrast one another in terms of friction just like how rounded studs and bladed bottoms do. On the following page, are calculations that prove that aluminum bottoms provide more friction than plastic studs. Research was conducted and it was found that the coefficient of friction for aluminum or metal against turf soccer fields is greater than the coefficient of friction for plastic against turf soccer fields. Through the equation: [force of friction = normal force x coefficient of friction], one can see that if the coefficient of friction is greater, then the force of friction will be greater. As well, the mass of aluminum is greater than the mass of plastic. Therefore, once again, mass will affect the normal force and increase the force of friction for aluminum studs. Rounded aluminum studs also have a greater length than rounded plastic studs; this extra length is used because when conditions are wet, the studs will sink into the ground. Having longer studs will prevent the shoe from fully sinking into the ground; keeping it elevated. This proves that aluminum studs will have more friction against the grass of a soccer field; and so it is recommended that they be worn during wet conditions in which more friction is needed.
Design Different combinations of designs that are already being used can provide customers will shoes that will be most useful in various conditions. From the previous section, we found that synthetic materials do not absorb water quickly, and bladed bottoms as well as the aluminum material for studs on the bottom of soccer cleats have more friction. Therefore, when taking into consideration weather conditions for the game of soccer, a good design for a soccer cleat to wear during rainy and wet conditions includes: bladed bottoms made from aluminum to increase the traction of the cleat; and the outer part of the shoe should be made from synthetic material so that water does weigh down the shoe. For dry conditions, the best combinations for a shoe include: rounded studs, made of plastic because you don’t want too much friction or it will be difficult to run. Aluminum studs are not needed; they will make the shoe too heavy. As well, kangaroo leather or any other types of leather can be worn in these conditions because they will not be ‘damaged’ by water. The leather material will provide you with a better touch since it is molded into the shape of your foot; it is lighter and thinner—making it more appropriate for dryer conditions.
New Design A good shoe must have enough traction, stability, flexibility, and protection. A new design of shoe that can be used in all weather conditions could be made of a new material called polyurethane. Polyurethane is a type of material that can be both flexible and rigid. It is resilient and durable so that it can withstand wet conditions; but it also has elasticity and flexibility like that of rubber. Thus, even though it is ‘tough’, its material is still able to be flexible to the movement of your foot. Another material that can be used is called vectran. Vectran is a material that is spun from liquid crystal polymer. It has exceptional strength (almost five times more strength than that of steel or aluminum) and rigidity, but it is also light. Thus, this material is useful because it will be able to withstand certain forces that will act upon the shoe during a soccer game (someone kicking or stepping on your
Design foot), but it is also light so that you can still maintain your speed and not be weighed down. Another element of the shoe that I would change is the heel protection. Instead of using a heel cup at the back of the shoe to reduce impact onto your foot; I would use a type of padding or new technology called d30. This material consists of various special molecules that are very malleable. What is special about this material is that when in normal conditions; it feels very soft just as foam would feel. But upon hard or sudden impact, the molecules in it will lock together, forming a solid material that will protect your heel. This will be useful in the shoe so that if you experience a greater force of someone hitting your foot in the game, this material will absorb that force and reduce the amount of force you feel. As well, to increase the power of the shoe, rubber ridges can be added to the top front curve of the cleat. These rubber ridges will have high rebound properties so that more power will be released from the shoe to the ball when force is applied through kicking. This will maximize the length and power of your kick. These rubber ridges not only maximize power, but they also protect your foot since they will also act as shock absorbers when your foot hits the ball. It will take that applied force and spread it out through the whole shoe so that you will not feel the impact as muchâ€”thus, it will not hurt when you kick the ball. Another important component of the shoe that should be modified or added is a strap that is attached to the tongue of the shoe and can be wrapped around to the bottom of the cleat. This strap should not simply be made of thread, but possible a stronger material such as a thick elastic that will not break easily. This strap will act as a seat belt does in the car. When your foot goes through sudden movement due to an applied force, it will control the footâ€™s movement and restrict some of the force so that your foot is not injured. As for the bottoms of the shoe, I would suggest sticking with blade bottoms that can be screwed in. This is because screw-in studs are very flexible for different conditions. Having aluminum and plastic bottoms will allow you to be prepared for both wet and dry conditions.
Calculations In this section, the calculations of the force of friction are shown between metal (aluminum) studs and plastic studs. Various masses of sample cleats were taken from the internet, as well as the value of the coefficient of friction of these materials against the surface of grass (soccer field). Together with the mass and the coefficient of friction, the force of friction was found.
Part 1: Plastic Studded Cleats From the internet, masses of cleats that were made of different materials with plastic studs on the bottom (rounded and bladed) were found. Example Calculation: Trial #1: The Nike Air Legend II cleat on the internet is said to have a mass of 0.312 kg. Also researched on the internet was that the coefficient of friction between turf (grass on soccer fields) and plastic is 1.2. Given: m= 0.312 kg; a= -9.8 m/s²; µ=1.2 Required: Normal Force; Force of Friction Analyze: Force of Friction = µ x Normal Force Solution: To find the Normal Force, first find the Force of Gravity Force of Gravity = mass x acceleration Fg = (0.312 kg) x (-9.8 m/s²) Fg = -3.1 N The Force of Gravity equals the Normal force because the shoe is not in the air (the forces going up and down are equal and they cancel out) Therefore, Fn = 3.1 N (it is positive because it is going up; instead of down like gravity) Now that we have the Normal Force; we can find the Force of Friction Ff = Fn x µ Force of Friction = (3.1 N) x (1.2) Force of Friction = 3.7 N Paraphrase: Therefore, the force of friction for a cleat that is made of kangaroo leather, and has rounded plastic studs is 3.7 N.
Calculations Part 2: Metal Studded Cleats From the internet, masses of cleats that were made of different materials with metal studs on the bottom (rounded) were found. Trial # 11: The Adidas adiPURE III TRX SG on the internet is said to have a mass of 0.317 kg. Also researched on the internet was that the coefficient of friction between turf (grass on soccer fields) and metal (aluminum) is 1.35. Given: m=0.317 kg; a= -9.8 m/s²; µ=1.35 Required: Normal Force, Force of Friction Analyze: Force of Friction = µ x Normal Force Solution: To find the Normal force, first find the Force of Gravity Force of Gravity = mass x acceleration Fg = (0.317 kg) x (-9.8 m/s²) Fg = -3.1 N The Force of Gravity once again equal the Normal Force because the shoe is not in the air (the forces going up and down are equal since they cancel each other out) Therefore, Fn = 3.1 N (positive because it’s going up; unlike gravity which is going down). Now that we have the Normal Force; we can find the Force of Friction Ff = Fn x µ Force of Friction = (3.1 N) x (1.35) Force of Friction = 4.2 N Paraphrase: Therefore, the force of friction for a cleat that is made of kangaroo leather, and has rounded metal (aluminum) studs is 4.2N Here is a table of values for more calculations done exactly the same as above. This chart shows the values of the force of friction for various outer materials in combination with various shapes of studs and various materials of the studs.
When we look at this chart, we can see that when comparing the rounded studs for metal and plastic; the metal rounded studs are typically heavier than the plastic rounded studs. As well, we see that when comparing the plastic studs; the bladed ones are heavier than the rounded onesâ€”this is because the bladed ones have greater surface area and a greater volume; thus, increasing the mass. If you compare the values of the similar materials between metal studs and plastic studs, you will notice that the metal studs always have a higher force of friction. This is because the coefficient of friction is greater between turf and metal than between turf and plastic. This means that more friction is present when an object made from metal rubs against a turf surface than when an object made of plastic rubs against a turf surface. This proves that the metal studs have more friction and thus; are more useful during wet conditions. If metal studs are not available, and only plastic studs are available, this chart shows us that usually bladed bottoms provide more friction than rounded bottoms of the same material. This is because the mass of a cleat with bladed bottoms tends to be larger. Since mass affects the value of the normal force and the normal force is used in the equation to find the force of friction; if normal force increases, the force of friction will increase as well. Thus, in rainy weather, it is most suitable to wear bladed studs that are made of metal (aluminum) because they provide more friction to prevent you from falling.
Cost, Production & Impact One of the conditions that will affect which cleat that people tend to purchase is
cost. If people are not serious about a sport, they will not likely spend a lot of money on sports equipment. On the contrary, if people are highly competitive and enjoy the sport very much; they will most like spend money and time to find the perfect equipment that will allow them to perform to the best of their abilities. Cost varies within cleats depending on the material they are made from. Synthetic materials tend to be cheaper than leather because leather has a greater impactâ€”it moulds into the shape of your foot. As well, having molded bottoms are of course cheaper than having screw-ins because having screw-ins means that you have two sets of studs. As well, it is much easier to produce molded bottoms since the screw-ins involve much more production to make individual screws and to create the technology that will allow the studs to be taken on and off the bottom of the shoeâ€”it is much more complex. On top of that, metal studs are more expensive than plastic studs because in reality, metal is a more expensive product that plastic is. Thus, put together, the screw-ins will typically be more expensive than the molded cleats. Players that are very serious about the sport tend to lean more towards screw-ins because they are more concerned about the weather conditions affecting the amount of traction they will have during the game (they have more knowledge about the sport so they know that in wetter conditions, they need metal studs, instead of plastic ones). Production for these cleats also vary by materials; production of leather tends to be less than synthetic materials because more synthetic materials are available for use; and they are easier to shape into a cleat. As well, there is much more plastic available, and so it is easier for production to occur for plastic studs. Therefore, with supply and demand, since production of leather material and metal studs is less, the price for these items will go up.
Cost, Production & Impact In the new shoe design, we see new products and materials being brought in such as d30, the vectran material, polyurethane, and the thick elastic band.
1. d30 • New technology that was just recently created by British scientists; thus, at this moment, the production for this certain material is quite low • Use and function hold much value to many customers; therefore, again with supply and demand, the value of this material will increase, thus raising the price • Through research, it was found that a ‘simple’ toque made of this material was set at a price of about $80.00. So, if you are planning to get a pair of cleats with d30 for heel protection, the price of the cleat will most likely be quite high. • But reliability and protection that d30 provides is truly unbelievable; so in the end, it’s what you value most.
2. Vectran • Purpose is to provide a light and flexible but also rigid and strong outer covering for the cleat • After researching, I found that a pair of Nike cleats called the Nike Mercurial Superfly contained some vectran material to decrease the weight of the cleats. The cleats were worth around $350; which is quite expensive compared to many other cleats. This is probably because once again, this type of material is quite new and took a lot of work to be discovered; thus its value is very high. • Even though this material may seem pricey; it reduces the weight of the shoe significantly and allows you to run at your maximum speed without feeling hardly any weight of the shoe.
3. Polyurethane • It is durable, it’s strong, and it even has elasticity so that your foot is flexible within the shoe; not restricted. • A Fila Forza III soccer cleat is made of polyurethane material and is priced at around $49.99.
Cost, Production & Impact • Price of polyurethane material is much cheaper than the price of production for vectran and d30 material. • This material was found many years ago, and as well, it is produced through chemical reactions. Therefore, the production cost is probably not as high as the other materials; lowering the price of the actual cleat. The price of this material seems more reasonable and it also has a very large impact on the shoe (a good buy). • It aids the foot by providing a strong protective layer but at the same time, it allows the foot to move freely, not restricting the applied force of the foot.
4. Elastic Strap & Rubber Ridges •
Reduce injuries and rubber ridges used to maximize the applied force onto a soccer ball
Most likely not too costly as rubber and elastic materials will most definitely not be more expensive than materials such as vectran.
Production will probably be quite simple as well; therefore, this function is a good choice because its cost is not too high but it serves a large purpose that will definitely have a large impact on the player.
5. Studs • Bladed screw-ins that have metal and plastic screw-ins. • Blades have a greater amount of traction and so even in dry conditions, when metal studs are not being used you will still have a good amount of friction that will allow you to move quickly from one direction to another. • Screw-ins would be useful so that upon weather conditions, one could just put on metal studs to increase friction. • More expensive because the area and volume of a bladed stud is slightly larger than that of a rounded stud. Therefore, for the screw-ins, a larger amount of the product is needed—thus, increasing the price. • Production for this part of the shoe will be more complex and more timeconsuming because they must somehow be attached to the bottom of the shoe which is rather difficult. • Higher prices for the cleat overall. But, impact on the player will be significant because it will allow the player to move much faster without falling.
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