The Physics of Basketball

Intro

Ironically, physics in basketball is fairly irrelevant. Instead the physics in basketball is simply interesting to people who really try to break down the art of shooting, passing, and dribbling. What I mean is that the “physics” in basketball is a product of a person’s memory. A person has a kinesthetic memory in how they remember how they shot from where and with a certain amount of velocity. This is achieved by hours of practice and playing. Basketball then becomes more of a series of reflexives behaviors and playing on instinct. However, understanding the physics of basketball can be very beneficial to a teacher of the game. Specifically, understanding the physics behind shooting, passing, and dribbling the basketball are the most beneficial and critical.

Shot

Perhaps the most interesting piece of the physics of basketball is seen in the shot. There are two main points of emphasis on shooting the basketball: the shot itself and the spin on the ball. First of all let’s establish two different types of shots the jump shot and the lay up. For the jump shot, there is little horizontal movement because the jump shot deals more with vertical movement. The ball itself is pushed off of his or her finger tips and the force and angle is applied upon release. Jeff Hornacek, NBA player, uses a different type of jump shot. He uses more of a running jump shot. Therefore, in the case of his jump shot there is more of a horizontal movement and a lesser amount of the vertical movement. “By not pushing the shot toward the basket, he doesn’t add velocity to the ball. Rather, allowing his running speed that he is traveling to be the horizontal velocity” (Kentridge). The running jump shot is a fairly rare type of shot used by players. The lay up, however, is a shot based more on momentum. “The velocity on the ball is the sum of the shooters speed and the balls speed” (Flores 2) so on the case of a lay up the ball doesn’t need as much force and is basically dropped into the basket, especially in a dunk. For anyone interested in knowing the required angle and velocity of a shot from anywhere on the court within 78 feet from the basket they can go to the website http://www.fearofphysics.com/Proj/proj.html.

Shooting a Free Throw

Let us now look specifically at a free throw. A free throw, just like any other shot, has the best chance of going in the more arc the shot has. When the ball comes straight down it makes the rim seem bigger than when a shot has more of a straight trajectory. Therefore, the most ideal shot would be one that comes nearly straight down into the basket; however, when shooting that type of shot it is nearly impossible to aim. Rick Barry, former NBA player, was an advocate of shooting a “granny” or underhand shot as his free throws. He shot his free throws underhand and for his career shot around 80 percent. He believes that more professional players, for example Shaquille O’Neal, that shoot a poor free throw percentage should shoot a granny shot even though it looks really goofy. Another advantage of the underhand shot is that it minimizes the drift of the ball. “The trick to keeping the ball moving along a single plane toward the basket lies in ‘minimizing the x-axis motion’… In other words you have to keep your elbows tucked in” (Rist). The underhand shot allows a player to have a lot more control over their shot. The traditional overhand shot requires movement from the wrist, elbow, and shoulder to make it easier for a person to shoot the ball with more error. However, despite all of these positive attributes to an underhand shot both Rist and Barry acknowledge that asking a professional player, or any player, would make them look “kind of stupid” (Rist).

Spin

The spin on the ball and its significance can be a fairly surprising topic to most people. The spin used on a shot during its time in the air is really irrelevant. The spin really only comes into use when the ball hits either the rim or the backboard. “The effects of air resistance of the ball are so small because of small velocities, so spin of a shot in air is not useful. What spin is useful for is for a better chance of the ball going in if the ball hits the rim” (Kentridge). Obviously, once the ball hits the backboard the velocity of the ball changes. Backspin on the ball will allow the ball to continue in a vertical path allowing the ball to have a greater chance of going in. “The backspin, after contact with the back rim or board, will result in a change in velocity opposite to the spin direction, changing an equal-angle rebound into a velocity more toward the net” (Willis). A ball without backspin will more than likely just bounce off the rim or backboard and will have a significantly lesser chance of going in. Another aspect of the importance of spin is that it transfers energy. “With the spin on a shot, some of the energy is transferred to the basket. This transfer of energy is from friction. When the spinning ball hits the rim, more energy is transferred” (Kentridge). One argument showing that physics isn’t really that important to basketball dealing with backspin is that “The backspin is mostly a calibration for the shooter to produce and reproduce the same shot. This is sometimes referred to by sports sciences and biosciences as muscle memory” (Cull).

Passing

Another aspect of basketball where calculating the physics can be interesting lies in passing. The idea of catching a pass can be analyzed using the equation m*v = F*t or F= (m*v)/t. In using this idea the greater the time is the lesser the force will be and thus the pass will be a lot easier to catch and not drop.

The idea of catching the perfect pass comes from the laws of motion and energy. If the ball is initially received with the elbows slightly bent the arms should be allowed to absorb the force of the on coming basketball and the ball should end up being caught close to the chest. This can be more easily explained in physics with the help of a couple simple formulas. It is known that in physics that the mass of an object multiplied by the velocity of the object equals the liner momentum of the object. It is also known that the momentum divided by the time it takes the object to impact is equal to the net force the object will have upon impact. In other words by the player catching the ball with arms extended and slightly bent elbows and allowing their arms to slow down the ball before hitting their chest they are increasing the time it takes the ball to impact. Since the momentum is divided by the time in the formula discussed above increasing the time will make the net force smaller when the ball is received into the chest. This will result in a nice soft reception of the basketball and smaller chance that the ball will be dropped. Flores

The art of passing the ball and receiving the ball shouldn’t be a very complicated process. Basically, as long as a person tries to catch the ball with their arms slightly bent it will be much easier as the person will be able to reduce the force by increasing the time of the pass.

Dribbling

Another important part of the game of basketball is dribbling the basketball. Obviously, a ball with more air in it will bounce higher than a ball that has no air in it. “The more air pressure a basketball has inside it, the less its surface will bend or deform during a bounce, and the more its original energy will be stored in the compressed air inside. Air stores and returns more energy than the material that the ball is made from” (Willis). Another way to look at dribbling the ball can be concerned with the potential and kinetic energy the ball has. When the ball is held the ball has potential energy. Upon its release to the floor, the potential energy converts to kinetic energy. “As the ball hit’s the floor the kinetic energy is stored as elastic potential energy. Because of this elastic energy the ball and the floor dent” (Flores).

Miscellaneous Information

Of course there are other miscellaneous pieces of basketball related to physics too. For example, the shoes must have good traction. Good traction means that the coefficient of friction between the shoe and the floor must be high. Also, a player uses static friction when planting their foot. This static friction allows a player to stop and turn without sliding across the floor because the static friction is greater than the sliding friction (Willis). A misconception that some people have is that great athletes seem to have a way of defying gravity and gliding in the air. However, all players fall at the same rate and the fact that they look like they are gliding is merely an illusion usually done by players extending their arms at the peak of the jump, bending their legs, and the fact that they are stopped by the rim but their legs continue “gliding” all allowing for this illusion to occur.

Conclusion

The physics used in basketball can be very educational and fun. However, it is not very practical as some other applications of physics. It is not very practical for a person to stop and calculate the angle, velocity, and position from which they shoot in order to consistently make a shot. Players instead rely on a kinesthetic memory built on repetition. However, for a real student of the game breaking down the pieces of the game into the physical reasoning can be extremely valuable. Often times coaches will present these physics applications without even realizing it and almost always without mentioning anything in the realm of physics. As much as the physics of basketball seems unimportant and ludicrous to calculate the principles are in fact very present and very valuable to a player without them even knowing they are doing physics.

Works Cited

Cull, Tom. Re: Why is putting rotation on a basketball when you shoot good. Picker International. 16 June 1999. 4 Oct 2003.

http://www.madsci.org/posts/archives/jun99/929552614.Ph.r.html

Flores, Darrick A. The Physics of Basketball. 30 April 2003. 4 Oct. 2003.

Kentridge School District. The Physics of Basketball. 4 Oct. 2003. http://www.kent.k12.wa.us/staff/trobinso/physicspages/PhysicsOf/Basketball/Physics%20of%20Basketball.html

Rist, Curtis. The Physics of Foul Shots: Underhanded Achievement. Discover Vol. 21 No. 10. 2000 October. 4 Oct. 2003. http://www.discover.com/oct/_00/featphysics.html

Willis, Bill. The Physics of Basketball. 2001. 4 Oct. 2003.

http://www.geocities.com/thesciencefiles/physicsof/basketball.html

Fear of Physics. Make Your Jump Shot. 4 Oct. 2003.

http://www.fearofphysics.com/Proj/proj.html

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