Physics Applied to Football
by Edward Padula
   


       

 
 
 

Speed is the single most important factor in football. Every coach understands this and therefore try to recruit players with good velocity. Effectively, how important is speed? Can we translate in numerical terms the relationship between velocity, body weight, and efficient blocking and tackling techniques? In this paper, I will introduce two concepts that may be helpful in understanding certain principles which we all coach, but not many comprehend completely. This discussion is the result of a long period of meditation on certain problems I faced as a coach.
In the past, I worked for four years as a defensive coordinator in the U.S. ( Ben Franklin High School, Rochester, New York), and twelve seasons in the Italian first and second divisions. In the last 15 years, I haven't coached, due to professional commitments ( working as a physician is a full time job ). Since I really love coaching, I used my spare time to study and reflect on past mistakes. This should help me become a better coach in the future. One of the most recurrent memories are those "long" days when we had to face much bigger teams. Very few coaches can say that their players physically dominated their opponents, in every game of every season they coached. Usually, it's a difficult game when your players have to drive block defensive men, with equivalent technical skills, which outweigh them, on the average of 20-30 Kg.. In this situation, what should a coach do to prepare his team? Is there a solution? In order to answer these questions, I will illustrate the two principles, I consider important.

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The first concept is a basic principle in physics. Each moving object can exert an energy; this energy is called kinetic energy. Kinetic energy is measured in joules (J) and can be represented by the following formula: 2 K=mv /2 where K is the kinetic energy, m is the mass, and v is the velocity of the object From this formula we can see that the energy of a moving object depends linearly on it's mass and exponentially on it's velocity. Translated in football terms; the energy that a player can exert on impact is linearly proportional to his body weight but exponentially proportional to his speed. Considering that in a collision, such as a football block, the object that has the greater kinetic energy will push the object with the lesser energy back , let's propose an example. An offensive guard who weighs 90K running at a speed of 7m/s ( 5.2sec in 40 yds ) blocks a nose guard who weighs 120Kg and is moving at 6m/s ( 6.0sec in 40 yds ) The block occurs with the players colliding head to head. 2 OG K=90Kg(7m/s) /2 = 90(49)/2 = 2205 J 2 NG K=120Kg(6m/s) /2 = 120(36)/2 = 2160 J From this example, we can see that a smaller offensive player can, basically, arrest the charge of a much larger defensive man, using his greater speed. The kinetic energy of the two players is equivalent, therefore the block will result in a stand-off, with neither player being able to drive the opponent back. The second principle is what I call "relative velocity". In the above example, the two players collide both moving in opposite directions, much as illustrated in fig 1. Now let's suppose that the defensive player was not moving in a direction opposite the blocker but was moving at an angle in relation to the blocker.
Fig 2 illustrates a defensive player moving at a 30 angle with respect to the offensive man's charge. The Y axis designates the direction of the offensive man's movement, the Z line indicates the defensive man's direction. It is clear that if the defensive player is moving at an angle, his speed along the Y axis is inferior to his actual speed. The velocity of the defensive player, in the Y direction, is represented by line Y1. The differences in length between line Y1 and line Z represents the decrease in relative velocity in the Y direction with respect to the actual velocity of the defensive player along line Z. Using a little bit of geometry, we can calculate that the relative velocity in the Y direction is .894 the actual velocity in the Z direction.

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Fig 3 and 4 represent the same situation with the defensive player moving at a 45 angle (fig 3) and a 60 angle (fig 4). In fig 3, the relative velocity of the defensive player in the Y direction is .709 the actual velocity, while in fig 4 the relative velocity of the defensive player is .447 the actual velocity. Fig 5 represents the defensive player moving at a 90 angle in relation to the offensive blocker. In this case the relative velocity in the Y direction will always be 0. No matter how fast the defensive man moves along the X coordinate, his movement in the Y direction will always be 0.
In conclusion, the greater the angle, between the direction of the oncoming blocker and the direction of the defensive player, the lesser the relative velocity of the defensive player in the direction of the oncoming blocker. Sounds complicated? Now if you are still with me, I will explain the importance of this concept. When we consider the "v" factor in our kinetic energy formula, we must use the relative velocity of the defensive player and not his actual velocity since we are interested in the speed with which the defensive player is moving toward the offensive blocker and not the effective speed of the defensive player.
Let's apply this concept to the above example, but instead of having the two players collide head on ( fig 1) we hypothesize that the blocker is coming toward the defensive player at a 60 angle ( fig 4). In this case, the relative velocity, in the Y direction, of the defensive player, will be .447 of his effective velocity. 2 OG K=90Km(7m/s) /2 = 90(49)/2 = 2205 J 2 NG K=120Kg(.447(6m/s)) = 120(7.19)/2 = 431 J From these calculations we can see that; the kinetic energy of the offensive blocker remains identical to the above example, while the kinetic energy of the defensive player, in the Y direction is reduced to almost one fifth. This difference in kinetic energies will result in a devastating block, even if the defensive player outweighs the offensive guard by 30 Kg. While in the first example a slight difference in speed resulted in a stand-off, in the second example, a change in direction from which the block is conducted, results in a more effective block, If the defensive player is blocked at a 90 angle ( fig 5 ), the kinetic energy developed by this player in the direction of the blocker will always be 0. This is usually the situation when we use crack-back blocks.
In this case, very small wide receivers, blocking at an angle close to 90, can literally "wipe out" much bigger linebackers. If you don't believe me, ask your players what block they hate the most, and I'll bet that the majority will say crack-back blocks. In the above dissertation, I tried to apply a little bit of physics to football. From this discussion what can we conclude?

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The first thing is that weight is important but speed is more so. We must teach our players to accelerate, to obtain the greater speed possible as quickly as possible. In this paper I talked mostly about offensive blocking, but the same principles can be applied to defensive tackling. Speed is the single most important factor in developing kinetic energy. It is important that we use drills that increases the speed of each individual player. We must also consider the importance of the velocity on impact. Many players may fear contact at full speed. They are very fast, but before impact they slow down drastically . It is important to understand that in a collision, the kinetic energy, of a moving object, is determined by it's speed at contact. Personally, I would prefer a slower player that accelerates on impact, than a faster player which slows down. Fear can cause youngsters to decelerate. This, not only results in an ineffective block or tackle, but is potentially dangerous. Now that we established how speed is important, let's examine "relative velocity". It was demonstrated that; the greater the angle between the direction of the blocker and the direction of the defensive man, the lesser the "relative" kinetic energy the defensive player can exert, thus the greater efficiency of the block. If we accept this principle, we should strive to design plays were head-on drive blocks are reduced to a minimum. A misdirect offense or other offensive systems that tends to "get the defensive player to lean the wrong way" may be effective. The speed and quickness of the offensive linemen permits a lot of cross-blocking, double teams, pulls, etc. An added advantage of this type of offense, is that the defensive player does not know from were the block is coming, this tends to create uncertainty which ultimately slows the defensive player further. Play action passing is also helpful in confusing the defense This type of offense minimizes size differences. Smaller players can become very effective against larger opponents, and when size difference is not significant, can become utterly devastating.

Edward Padula
Coach
Email: Edward Padula


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