## Physics of Tennis

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When observing a tennis match, one may notice that all three of Newton’s laws are in action.  Newton’s first law states that an object at rest stays at rest and an object in motion stays in motion at the same speed, with the same direction unless acted upon by an unbalanced force.  Using a tennis racket to strike a tennis ball is a prime example of unbalanced force acting upon an object in motion.  Once the ball is struck it flies over the net before being pulled down towards the ground by gravitational pull.  If it weren’t for gravity’s existence, the tennis ball would continue to fly in a straight line forever.  Newton’s second law suggests that force is equal to mass times acceleration.   A serve illustrates the equation that Newton was speaking about.  Take the weight of a tennis player’s racket and multiply it by the speed at which a player swings their racquet and you will have figured out the total amount of force that was exerted by the tennis racket onto the ball.  Newton’s third law suggested that for every action there is an equal and opposite reaction.  Whenever a tennis player strikes a ball the force of the racquet striking the ball and the force of the ball striking the racquet both act upon each other.

Similar to what I talked about in my blog focusing on the physics of hitting a baseball with a bat, tennis racquets also have sweet spots.  The sweet spot is the spot on the racquet that when hit feels the smoothest on the player’s hands.  Also similar to what we talked about regarding baseball, when a tennis player strikes a ball far from the sweet spot the player experiences an uncomfortable vibration that runs through his racquet and onto his hands.  During a serve, kinetic energy is stored in the form of motion as the ball travels through the air.  For this reason, players are capable of serving their hardest when they strike their serve at its peak when tossed up in the air.  This maximizes the use of gravitation potential energy, or the energy stored in the form of height.  Most tennis players attempt to use different forms of topspin, backspin, and sidespin when they hit their shots.  The friction between the ball and the racquet’s strings is responsible for causing the ball to spin forward. (1) Professional tennis players often slide their racquets over the ball to put topspin on their shots.  On the contrary, players are capable of putting backspin on their shots by performing a slicing motion.

1) http://www.unc.edu/~sheng1/spin.htm

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I remember being a kid and watching old highlights of Larry Bird wondering to myself how the heck he was such a consistent shooter.  The man exhibited an overwhelming amount of confidence out on the basketball court; it was as if every time the ball left his fingertips he knew it was going in.  I listened to Larry talk about his shot and remember hearing him say that when he practiced shooting free throws he would line his right foot up with his right elbow and his right eye.  By setting up his body in such a manner Bird was able to maintain consistency at his release point.

When a shooter releases a basketball the distance it travels occurs as a direct product of the amount of force that he/she applied.  The further away from the basket the shooter is, the more force they will be required to put on a shot if they want to get it in the hoop.  The spin a shooter puts on the ball occurs as a result of their release.  A good jump shot typically has a good amount of backspin so that if the ball were to ricochet off the backboard it would come off at a downward angle into the hoop.  The term used by most basketball connoisseurs to describe the trajectory at which the basketball flies through the air is “arch”.  The more arch a shot has, the more likely it is to come down in the hoop. This is because when a ball comes straight down it makes the rim bigger.  Think about it, dropping a ball down into a hoop is a lot easier than trying to shoot it in at an angle because you have more of the basket to work with.   In order to figure out the correct arch to use, a shooter must take into consideration their height, how far away from the basket they are, the weight of the basketball, and how tall the hoop is.  Their last step would be to figure out the correct combination of what angle they would like the basketball to fly through the air at when they shoot it and what speed they should shoot the ball at.

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

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

## Physics of Ice Hockey

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Physics of Ice-Hockey

The velocity and force with which a puck can be shot in an ice-hockey game can get a little bit scary.  Most professionals who understand the physics behind taking a powerful slap shot are capable of putting the puck on net at velocities of well over 100mph.  To properly take a slap shot, a player must first lift his stick up over his shoulder, cock it back, and strike the ice just behind the puck.  Different brands of sticks have various levels of flex capabilities that allow players to bend their sticks to different extents.  When a player flexes, or bends, his stick, energy is stored in the blade.  As a player makes contact with the puck during a slap shot, he shifts his weight and flicks his wrists.  This rotation causes the stored energy to release off of his stick and transfer to the puck. Once the puck is struck, the amount of kinetic energy that has been supplied onto it is equal to the amount of energy stored in the stick.

Energy goes from player to stick, then from stick to puck.

The physics of skating are also very interesting.  Professionals are capable of skating both frontwards and backwards at speeds far faster than a human would be capable of running.  This is because of the capabilities players have to gain speed quickly by digging the edges of their skates into the ice and pushing off.  The low friction of a skate’s blade is what allows a hockey player to glide all over the ice’s surface while making it appear to be an effortless motion. (1)  The width of the skate’s blade is about 3 mm.  The skate’s design allows for the skate to successfully glide over irregularities in the ice. (2)  We see Newton’s third law, which suggests that whenever one object exerts a force on a second object, the second exerts an equal and opposite force on the first.  This explains why players must push their skates backwards in order for the ice to push them forward.

2)   http://www.hockeyphysics.com/icehockey.html

## Physics of Football

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The role that physics plays in tackle football is more relevant now than ever before.  Just this past year National Football League officials changed the rules of the game in order to avoid some of the intense physical danger that comes along with one human tackling another.  The commissioner put through a rule that moved kick-offs up a full 10 yards from where they used to be.  The point being to discourage kick returns from taking place by making it incredibly easy for the NFL’s kickers to kick the football out of the back of the endzone for a touchback.  The physics behind the contact players make throughout the course of a football game is mind-shattering; I mean that in both a literal and figurative sense.

With the mass and speed of NFL players steadily increasing, the momentum behind each and every hit thrown on Sundays has grown to be more and more dangerous.  This has made physics more relevant today in the NFL than it has ever been before.  Current players are more frequently getting concussions and ex-players are coming out and saying their lives have been ruined because of the violent nature embedded in America’s most popular sport.  So, let’s take a look at the physics behind all the madness.

When two players are running full speed at each other on a football field they build up their momentum.  At the point of contact, a tackler must apply an impulse by hitting the ball carrier. Impulse is the product of the applied force and the time over which that force is applied. (1)  Figuring out whether the ball carrier or the tackler has more momentum will allow us to determine which of the two will be knocked backwards. In other words, if a running back hits the hole and makes contact with a linebacker who has less momentum than he does, the linebacker will be driven back and the running back will gain more yards.  If the linebacker is able to build up more momentum than the running back, then he will be able to knock the running back backwards.  The conservation of momentum theory suggests that the total momentum of each player must remain constant both before and after their collision.  This means that if a linebacker and a running back hit each other at an equal momentum they will stop at the point of contact, not a step further in either direction.

## Physics of Golf

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Physics of Golf

The game of golf has been troubling people since the day the Scots invented it back in the 15th century.  How can hitting a little ball that isn’t even moving at a similarly still target be so difficult that golf experts say in order to play “bogie” golf it would take an average player six years of regular play and weekly lessons? (a bogie is one stroke above par)  Well, there are both mental and physical aspects that go into being a successful golfer; the physics behind the sport play a prevalent role in understanding both of those aspects.

The golf swing is a prime example of angular motion in action.  The faster a golfer is capable of getting his/her club head to go at the bottom of their swing, the more kinetic energy they will be capable of transmitting from the club head to the ball.  This is because kinetic energy is proportional to the mass of the club head and the square of its velocity.(1)  Similar to what I talked about when I described the physics of hitting a baseball, when a golf club makes contact with a golfball the ball is deformed at the point of contact.  This is where ball selection comes into play on the PGA tour.  Golfers who choose to hit balls with harder cores will not experience the same amount of deformation as the golfers who choose to hit softer balls.  The balls with harder cores provide a more efficient transfer of kinetic energy, causing the golfball to go further. At first glance it seems silly that any professional golfer would choose to use the soft cores but in order to maximize the amount of energy stored inside of the golfball professional golfers must relate the speed of their swings to what type of balls they choose to hit.

After a golfer makes contact with the ball there are three important factors that determine how his shot turns out.  The first factor is the speed at which the ball comes off of his/her club.  The reason Tiger woods can hit the ball so far is because the ball comes off of his club at a speed that is about 25 MPH faster than that of his competitors. (1)  The second factor is the angle at which the golf ball comes off of the club and propels through the air.  The final factor that has an affect on where the shot ends up going involves the spin put on the ball by the club at the point of contact.

## Physics of Soccer

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Physics of Soccer

Every soccer player has spent at least a few weekends out in their backyard attempting to figure out how to “bend it like Beckham”.  Back when I was just a young lad I remember building up make-shift soccer nets in my backyard next to my swing set.  I had seen the videos of England’s free-kick master David Beckham bending the ball across the entire net and beating opposing teams’ respective goalkeepers time and time again.  I was dumbfounded by the way he could kick the ball; I simply could not make sense of how he was able to get the ball to fly through the air in such an unstoppable manner.  So to try to figure it out I spent hours upon hours and days upon days in my backyard aiming my shots at the swing set, hoping that one day the ball would bend its way into the back of the net.  Unfortunately for my swing set I could never figure out the method behind Beckham’s free-kick magic.  But now that I’ve grown older and wiser I have come to realize I was merely one physics lesson away from learning the trick.

In 1852 German physicist Gustav Magnus was credited with the first explanation of the lateral deflection of a spinning object. (1)  At the time, his work happened to be aimed at figuring out the reason why spinning shells and bullets deflect to one side; his conclusive explanation was equally applicable to soccer balls.  When a soccer ball is kicked a specific spin is applied to it.  The air around the ball travels more quickly on the side of the ball that is moving in the same direction as the airflow.  According to Bernouilli’s principle, this reduces the pressure. (2) On the opposite side of the ball the opposite effect is taking place because the air is contrarily traveling slower relative to the center of the ball.  This imbalance of force causes the ball to “bend” laterally.

When David Beckham attempts a free kick, there are two types of force playing into the amount of spin he is capable of getting on the ball.  These forces will ultimately determine how much he is able to get his kick to bend.  These two separate forces are known as the lift force and the drag force.  The lift force is what accounts for the Magnus effect, which moves the ball sideways.  The drag force acts in the opposite direction of to the path of the ball. (1)  By understanding the physics behind taking a nice free kick, players can figure out how many rotations they will need per second from a given distance, how hard they will need to kick the ball, and where they will need to aim it in order to get it to wind up in a specific location.

3)   http://www.youtube.com/watch?v=1DoYkUDRk8Y – Watch David Beckham bend in a free kick for a goal

4)   http://www.youtube.com/watch?v=Ha09dfNWfw4&feature=endscreen&NR=1 –Watch David Beckham bend a ball in multiple different ways over a body of water and into the net.

## The Physics of Baseball

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There are two main areas in the game of baseball where physics play a major role: pitching and hitting. When a pitcher pitches a baseball, it must travel sixty feet and six inches to reach home plate.  As a former pitcher, the importance of a focused windup was always preached to me.  When a pitcher goes into his wind up he attempts to use his body to its best ability in order to provide a high amount of energy to the ball.  A fundamentally sound wind up requires a pitcher to produce a motion that involves the biomechanical principal known as “sequential summation of movement”. (1) This principal suggests that the largest body masses must move first, followed by the smaller ones. (2) In a pitcher’s wind up, his first move is to step back, creating a weight shift through his legs.  He then rotates his hips, lifts his legs, and thrusts his body forward.  The pitcher pointing his shoulder, pumping his arms and flicking his wrist follows up the use of his larger body masses.  How hard a pitch is thrown is most greatly effected by the power generated in the pitcher’s legs and his use of proper arm trajectory.

Hitting a small round ball thrown at a high velocity with the “sweet spot” of a round bat is widely regarded as the toughest thing to accomplish in all of sports.  The sweet spot on a bat is typically about 6.5 inches from the end of the bat.  If a hitter is going up against a 90 mph fastball, impact is set to occur about 400 milliseconds after the pitcher releases the ball.  By making contact as little as 7 milliseconds too early or too late a batter’s swing will result in a foul ball.  In the 400 milliseconds between release and contact, a hitter must see the pitch, judge it’s speed and location, and decide where they must swing in order to make contact on the sweet spot.  Hitting the ball on the sweet spot makes the vibration caused by the ball hitting the bat cancel out.  Since less energy is used on that vibration, more energy can go to the ball. (3) As I know all too well, when a hitter swings and misses the sweet spot, it can result in a vibration that stings his hands and forearms.  At the point of impact (when the hitter’s bat makes contact with the ball) thousands of pounds of force cause the baseball to compress to roughly half of its original diameter.  This causes the ball to bounce off of the hitters bat at dangerously high velocities.

1) http://www.exploratorium.edu/baseball/putting_something.html

2) http://www.physics.usyd.edu.au/~cross/baseball.html

3)http://science.discovery.com/video-topics/sports/the-physics-of-baseball.htm

## Intro to Physics of Sports

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Michael  Philbin-Pelland’s Physics Blog

7 Posts

-Baseball – Football – Hockey – Basketball – Tennis – Golf – Soccer –

In this blog, I will briefly describe the physics involved with seven different sports.  I have tried my hand at each of these eight sports at one point or another, so I am interested in figuring out the science behind being successful at each of them.  The eight sports I will post about are baseball, football, ice-hockey, basketball, tennis, golf, and soccer.  The study of the physics of these sports can also be referred to as “sports biomechanics”, which is the branch of physics that deals with analyzing the actions of forces.(1)