How is football related to physics

This assumes that the initial launch velocity v o of the football is kept constant. Collision Between Players When one player attempts to tackle another player, a force is exerted on each player, and on each player the force vector is equal and opposite to the force vector acting on the other player Newton's third law.

The figure below illustrates a general situation in which one player collides with another player. Body A can be thought of as the player doing the tackling, and body B can be thought of as the player carrying the ball. These forces act at the effective contact point C between the two players, during the collision. Based on a book by Timothy Gay, a professor of physics at the University of Nebraska-Lincoln: The Physics of Football , the center of mass point G and the effective pivot point P A of body A are both at the best position when they lie on the line of action of the impact force F BA , where the line of action is represented by the dashed line.

When body A the linebacker is pushing on body B before body A establishes firm contact with the ground at pivot P A , then having point G on body A lie on the line of action of F BA will ensure that there is no torque on body A as a result, body A does not rotate. Once body A establishes firm contact with the ground, and the line of action of F BA passes through the effective pivot point P A of body A, then body A will not rotate because there is no torque to do so. However, the ball carrier body B will have a torque exerted on him due to the force F AB which creates a torque about his effective pivot point P B with the ground.

This will cause body B to rotate and possibly fall over. This analysis is a result of assuming both bodies behave as rigid bodies, and experience a simplified case of two-dimensional planar motion. A lower L A for body A means that, in general, there is a shorter moment torque arm perpendicular distance between F BA and P A than if body A were standing up straight.

This means that it is harder to rotate body A. Consequently, it is easier to rotate body B and cause him to fall over than body A. The collision between both bodies can also be analyzed using the conservation of momentum, assuming a simplified case of one-dimensional motion, and negligible ground external forces acting on the players during impact.

Suppose v GA is the velocity of the center of mass of body A immediately before impact, and v GB is the velocity of the center of mass of body B immediately before impact. Football Bounce When a football bounces, its motion is much more unpredictable than the bounce of a regular ball.

The reason is because of the shape of a football, which results in contact forces with the ground having a largely variable line of action. Rod Cross, a physicist and retired academic of the University of Sydney, has written extensively on this subject. I base the following brief analysis on a paper that he wrote: Bounce of an oval shaped football. The shape of a football can be well approximated as a mathematical shape defined by a prolate spheroid.

The bounce of a football is inherently a three-dimensional motion, but for the sake of simplicity, an analysis can be done for bounces that occur strictly in two-dimensions planar motion. The following figure shows a football bouncing in two dimensions, with the different bounce stages shown; showing the football just before the bounce, during the bounce, and just after the bounce. Note that during the bounce the football makes contact with the ground, and rotates a bit, such that its orientation changes.

During this rotation, the football can slide on the ground, roll without slipping , or undergo a combination of both. The red dot represents the center of mass of the football.

During the impact stage, when the football makes contact with the ground, a basic two-dimensional analysis can be performed using the equations for impulse and momentum. To start off, consider the figure below showing a free-body diagram of the football as it makes contact with the ground, with sign convention as shown. There was also more spin if the offset position was further from the centre of gravity.

Two other interesting effects were observed. First, if the offset distance increased, then the foot touched the ball for a shorter time and over a smaller area, which caused both the spin and the velocity of the ball to decrease. There is therefore an optimum place to hit the ball if you want maximum spin: if you hit the ball too close or too far from the centre of gravity, it will not acquire any spin at all.

The other interesting effect was that even if the coefficient of friction is zero, the ball still gains some spin if you kick it with an offset from its centre of gravity. Although in this case there is no peripheral force parallel to the circumference of the ball since the coefficient of friction is zero , the ball nevertheless deforms towards its centre, which causes some force to act around the centre of gravity. It is therefore possible to spin a football on a rainy day, although the spin will be much less than if conditions were dry.

Of course, the analysis has several limitations. The air outside the ball was ignored, and it was assumed that the air inside the ball behaved according to a compressive, viscous fluid-flow model. Ideally, the air both inside and outside the ball should be included, and the viscosities modelled using Navier-Stokes equations. It was also assumed that the foot was homogeneous, when it is obvious that a real foot is much more complicated than this.

Although it would be impossible to create a perfect model that took every factor into account, this model does include the most important features. Looking to the future, two of us TA and TA also plan to investigate the effect of different types of footwear on the kicking of a ball.

Meanwhile, ASICS is combining the Yamagata finite-element simulations with biomechanics, physiology and materials science to design new types of football boots. Ultimately, however, it is the footballer who makes the difference — and without ability, technology is worthless. So what can we learn from Roberto Carlos? If you kick the ball hard enough for the airflow over the surface to become turbulent, then the drag force remains small and the ball will really fly.

If you want the ball to curve, give it lots of spin by hitting it off-centre. This is easier on a dry day than on a wet day, but can still be done regardless of conditions. The ball will curve most when it slows down into the laminar flow regime, so you need to practise to make sure that this transition occurs in the right place — for example, just after the ball has passed a defensive wall.

If conditions are wet, you can still get spin, but you would be better off drying the ball and your boots. Close search menu Submit search Type to search. Topics Astronomy and space Atomic and molecular Biophysics and bioengineering Condensed matter Culture, history and society Environment and energy Instrumentation and measurement Materials Mathematics and computation Medical physics Optics and photonics Particle and nuclear Quantum.

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Reset your password. Please enter the e-mail address you used to register to reset your password Enter e-mail address. Registration complete. Everyday science Feature The physics of football 01 Jun The drag coefficient drops suddenly when the airflow at the surface of the sphere changes from laminar to turbulent. The position of the discontinuity depends on the roughness of the surface of the ball.

Footballs are relatively smooth and so need to be kicked relatively hard to gain enough speed to move into the turbulent phase. At high speeds, the drag force falls, which means that the ball does not slow down as much as expected. This illustration shows the deformation on a leg and ball, ranging from pink the lowest through blue, green and yellow to red the highest.

These studies have confirmed what most footballers know. Share: Facebook Twitter. Well not every sport, as there is a list of unusual sports , extinct sports and newly created sports. How to get on these lists? See What is a sport?

Throwing a Football. Any comments, suggestions or corrections? Please let us know.