 Understanding how things happen in a basketball game, from a physics point of view, is not necessary for a good player. A basketball player knows instinctively what to do in any given situation. Through thousands of hours of practice and game play, his brain has the correct sequence of muscle movements 'hard-wired' into it, much like you or I can walk without thinking about where to move the legs, and by how much. This is called 'kinesthetic memory'. A good pro basketball player has these game play reflexes because he began learning the moves as a child, when the brain is most receptive to imprinting a reflexive behaviour. It can be argued that such imprinting, through constant practice, must begin in childhood if the athlete is to become a star pro player.  Nevertheless, it can be very useful to understand the physics behind some of the skills in basketball. A physical analysis of a player's movements, combined with a knowledge of the correct forces to apply at the right time, can be used to make a good player better. Scientific analysis like this is used in many sports, from figure skating to baseball. Let's look at some of the simpler physics rules being applied in every basketball game.  Spin on the BallSpinning the ball when you shoot is not done to affect air resistance, or to make air resistance cause the ball's path to curve, as is the case in baseball.  Basketballs move too slowly for that to happen. Once the basketball leaves the shooter's hand, it travels in an unchanging parabolic path. So what's the purpose of backspin? Backspin on the ball is used to help it to bounce into the net when it hits the rim. It will usually hit something, unless the throw was very high. 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. This makes it more likely that the ball will go in.
 Receiving a Pass:The impact of a hard pass can be lessened, making it less likely the ball will knock the wind out of you, if it is caught into the body. The ball coming at you has momentum, m·v. By increasing the time over which you decelerate the ball, you lessen the force. In other words, since m·v = F·t, then F = (m·v) / t ... increasing t causes F to get smaller. This is the same principle that makes an air bag in your car work. The time over which you decelerate is lengthened, resulting in a lower force. Of course, catching a ball into your chest has other benefits. It makes it less likely you'll drop the ball, and harder for someone to grab.   Bouncing the Ball: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 energy more efficiently than the material that the ball is made from. If the ball is underinflated, some of its energy is wasted in deforming the ball as it bounces, and the ball will not rebound very high. For the most elastic collision possible between the ball and the floor, you want a highly pressurized ball. (But you knew that already, didn't you! Now you know why!) The material you bounce the ball on is also very important. Think about how high it would bounce on a carpeted floor. A soft floor material will flex when the ball hits it, and this will steal some of the ball's energy. Clearly the harder the surface, the better.  Starting, Stopping, and Changing Direction:A players' shoes must have good traction, which is the same as saying that the coefficient of friction between the shoe and the floor must be high. Friction is the force that opposes the motion of two surfaces that are in contact. Every surface is rough, on the microscopic scale, and when two surfaces come in contact, the high points on each surface temporarily make contact. The opposing or attracting forces of the surface molecules cause a 'frictional' force. A basketball player will also make use of static friction; a foot firmly planted, rather than slipping across the floor, will provide more friction when he has to stop or turn suddenly. This is because static friction ('pushing off') is greater than sliding friction ('sliding'). It is also why shoes must have a good grip on the floor in any direction you push off from, and why some shoes are unsuitable for basketball ... they may have lots of forward traction, but slip too easily when pushing sideways. It's just like driving ... spinning tires have less frictional force than non-spinning ones. ABS systems keep the tires from sliding, and maintain more friction.  Hang Time:Pro basketball players seem to float in the air while they're at the basket with the ball. Of course, this is just an illusion; they fall at the same rate as they rose into the air, assuming they don't make contact with anything. What makes the time seem longer is probably because after their bodies reach their highest point, they extend their arms upward, giving the illusion that they're still going up. They are also moving forward when they jump, which also affects our perception of time. Here's an example. Imagine firing a bullet from a rifle, directly at a monkey hanging from the branch of a tree a kilometre away. If the monkey lets go of the branch just as you fire, will you hit him? Leaving aside the environmentally sensitive issue of whether or not we should be shooting monkeys out of trees, this is actually a well-known physics problem. In fact, the moment the bullet leaves your gun in a horizontal line, it will begin to fall. It will fall with exactly the same acceleration downwards as the monkey. Regardless of how far away the monkey is, when the bullet reaches the tree, it will have fallen the same distance as the monkey. It will hit him! This seems unlikely, since we usually visualize bullets as travelling in a straight line. But as any hunter will tell you, they do fall. If aimed horizontally, the bullet will hit the ground in the same time another bullet would, if you dropped it from the same height as your gun. The 'hang time' of a pro basketball player at the net seems longer because he is moving forwards and upwards. It is harder to consciously be aware of how long it took him to go up, when he is also moving forwards. But if you used a stopwatch and a slow-motion replay, you would discover that the time from when he left the floor to when he stops moving upward is exactly equal to the time he takes to fall, and there is no hang time! The instant he stops going up, he starts to fall. But this is hard to see when things happen fast and there is forward movement.  Foul Shots:For a player of given height, the exact force and direction necessary to give the ball a velocity that will result in a basket can be calculated exactly. There are no complications. The difficulty is that these quantities can't be measured exactly by eye, and the application of the force is through muscles which can't be controlled perfectly one hundred percent of the time. So in this case, physics won't help at all! So how does a professional basketball player manage to make so many shots successfully? The answer is 'kinesthetic memory' again. A player cannot possibly calculate the correct angle and force for a shot, and even if he knew what they were, couldn't reliably make his muscles do exactly what was necessary. Instead, the player practices the shot over and over, thousands of times. Golfers do this ... a pro golfer must hit tens of thousands of shots, practicing hours every day, year after year, before there is any hope that he will be good enough to play in the pro leagues. What the repetition does is familiarize the athlete with what a good shot feels like, and what movements he was making to achieve that perfect shot. It's the same in all pro sports. In the case of a pro basketball player, he makes the shot nearly every time because he 'lets his muscles do it' ... he does it exactly the same way he's done it thousands of times before, and doesn't have to think about it.  Layups:A good layup happens when the player does not take a shot, but uses the speed of his body to put him near the net. He just has to drop the ball in! (O.K., maybe slam it in.) The point is that it would be very difficult to shoot while you are also moving forward. Good players can make passes this way ... throwing while they are in the air, moving forward, and twisting around. But shooting at the basket, which is a much smaller target and at a different distance each time you do it, would be a hard shot to make while you're moving towards the net. (The ball's velocity would be the sum of your speed and the ball's) .Players always stop to shoot, to allow 'muscle memory' to do the shooting for them. Rather than practice this difficult skill, throwing from farther away while moving towards the net, players master the skill of the layup. They move their whole body through the air, protecting the ball as long as possible, and put it in the net when they're so close they can't miss. |