The Physics Behind A Tennis Serve

The Physics Behind A Tennis Serve



The serve in tennis is how every rally begins, each player will alternate serving after one player has served a game, they will play games competing to win enough to win the set, and a set is done once one player wins 6 games. The purpose in tennis is to be the first one to win either 1, 2, or 3 sets depending on where you are playing. Serving is a very important aspect of the game, when a player serves they are expected to win the game and when they loose it is considered to be a loss of serve, making it very important to being successful.

All serves begin with the player tossing the ball up and then striking the ball, one of the main reasons professionals are much more successful and powerful is because they toss the ball higher, as well as into the court. This allows the hit to be angled downwards and if angled correctly will still land in the opposing service square, the added height of their contact point means the do not have to ark the ball which will result in a faster serve.. As well the ball being thrown into the court will increase the hitting force of the server adding to the speed of the ball.

Another important part to a serve is right before you jump to hit the ball and during the jump. During this time professionals will; rotate their body, extend their arm, and snap their wrists as seen here. This is known as the "kinetic chain principle" which in a tennis serve is the idea that your body when it starts to move, will transfer speed and power into the next part of your body, the jump begins to transfer energy into the rotation, the rotation transfers energy into the arm movement. This allows you to serve at the highest speed possible.



The final key part of a serve is getting it inside the opponents serving box. There are two important factors here, the speed of the serve, and the amount of spin on the ball. The speed of the serve is important, because a slow serve has more control, they can be hit with an ark as well as a flatter shot, and still go in. A faster serve is much more difficult to keep in, professionals make up for their fast serves by putting a lot of spin on the ball (an average of 2400 rpm in the Association of tennis professionals). The spin creates the same effect that was discussed in the curve ball post; the Magnus force. The top spin on the ball will cause the ball to move downwards and helps to land a serve in.



The green line shows the path you want your ball to take, to land into the opponents service box.

Speed skiing And Physics

Speed Skiing And Physics



Speed skiing is a sport where the purpose is to be able to go down a hill as quick as possible in an attempt to make it to the bottom of the hill in the least amount of time. It is believed to have originated in the year 1898 when a skier allegedly went skiing and reached a speed of 139 km/h. Recordings of speed skiing began in the year 1932 even thought the sport had existed for many years before, and it became an official Olympic sport in 1992.

In speed skiing in order to be successful you must focus on two key aspects of the sport. One of those aspects is to reduce friction. The equipment is very important in reducing friction, the skis used in speed skiing have the largest area in which the ski is touching the snow. This actually helps reduce friction by distributing the weight more evenly, This would  cause a problem though, if the skis were unstable and did not stay in contact with the snow, manufacturers avoid this by making skis very rigid, and are on average 25 pounds.

Another way skiers reduce friction is through air resistance, as you can tell skiers wear very aerodynamic suits. The suits are skin tight and coated in polyurethane, this coating gives the suit a density which will not allow low pressure zones to form on the skier, distributing the air resistance, and maximizing speed. Another aspect of the suit is the spring in the bottom the boot the skier wears. This spring puts the person into a forward position, and helps them be more aerodynamic because they are having less wind hit them than if they were in an upright position.

When an object is aerodynamic, it maximizes efficiency as far as movement goes. With skiing this is done through the materials and equipment they use which allows air to flow by with minimal resistance and friction. The equipment and positioning of the skier is shown to be very effective in this website's experiment as made evident in the raw data part of the website.

The other aspect of speed skiing is harnessing the force of gravity, gravity is a downward force the earth exerts on us, it is based on the mass of the skier. If the skier is heavier they will generate more speed than someone who has a lower mass, although they also tend to have a larger surface area that comes into contact with the wind, causing them to be slower. The ideal skier would have a combination of mass and a small size to avoid the wind resistance

The Physics Behind A Football Hit

The Physics Behind A Football Hit



The sport of football developed off of rugby and is a very physical game. From a defensive perspective the point of the game is to tackle the ball carrier and hold him to the least amount of yards possible. The sport has many aspects which can be analysed through physics, including hits and the equipment.

When someone gets hit, there are many factors to consider, the two masses of the people going into contact, the speed of both players, as well as if the hit is two players running directly at each other. Often people unfamiliar to the sport, will assume that the biggest players -who tend to be around 300 pounds in the National Football League (NFL)- will deliver the most powerful hits. This though tends to be incorrect though, as the intensity of the hit they can deliver is based on their mass and speed. Those players to lack the physical ability to go fast enough to make powerful hits, the position that tends to have the best combination of speed and mass is the defensive back, they have the speed to cover all offensive players, and are in excellent shape to give them the most power. Marcus Truffant of  the Seattle Seahawks weighs 199 pounds and can complete the 40 yard dash in 4.56 seconds, giving him the capability of a tackling force of 1600 pounds.

The developments in the aspect of the shoulder pads has been a change of materials making them lighter and easier for players to move in, but they also have changed the arrangement of padding, aligning it to form right angles, to deflect contact from the player getting hit.


The following video shows an analysis of a football hit which had enough force to cut the ball carriers jaw open. It applies the conservation of momentum into the hit, calculating the velocity of both players before the hit and the result of the hit, both players going towards the sidelines.
http://www.youtube.com/watch?v=cGhKVNUfPcc

Bowling Advancements Explained By Physics

Bowling Advancements Explained By Physics

Bowling is believed to have originated from Egypt nearly 5000 years ago, making it one of the oldest sports known to man. Many features of the game have changed though, from the original limestone flooring and stone ball that they used to use back in those days. In the past twenty years the sport of bowling has drastically been changed from a game of skill and power to a sport where an understanding of physics and the right equipment can benefit you more than athleticism.

Present day bowling is played on proprietary synthetic bowling lane surface, no longer do they us maple or pine trees. Although this surface is designed for bowling, it would still not last very long with constant abuse from bowling balls, so they have put a mineral oil on the first 45 feet (out of 60 feet) of the lanes, and this is done once a day.

This has been taken advantage of by bowling ball companies who were working to combine speed and a greater angle of entry (between the head pin and the pin directly beside at a sharp angle will increase chances of a strike). They have created a ball with an outer layer with resin on it which has a very low coefficient of friction with the mineral oil part of the lane but has  a very high coefficient of friction on the last 15 feet with out oil on it, this is shown very well in this video at the 1:30 part of the video they compare two bowling balls, and the blue one does not have as strong of a curve at the end because it is not a resin ball, but the black one curves at a much sharper angle because it is a resin ball  http://www.youtube.com/watch?v=nx_RF2JtEbc.

As well companies have been developing bowling balls with different cores, which directly affects the radius of gyration, the radius of gyration relates to an object in rotation, the distribution mass from the center of the object, and the moment it enters inertia. A low radius of gyration will allow the ball to spin with less hand requirement then a higher radius of gyration, a higher radius of gyration will help your ball stay on line longer, while a lower radius of gyration, will give your ball more reaction to spins.

The Physics Behind The Slam Dunk

The Physics Behind The Slam Dunk

The slam dunk is a play in basketball where the shooter takes the ball and instead of shooting from a distance, the shooter gets within one jump away from the rim and throws the ball directly through the rim. In the early 1940's the slam dunk was just making its way into the NBA (National Basketball Association), but instead of being a common and exciting play, it was used as a way to disrespect your opponents and often lead to a very physical game. Things began to change though as more athletes realized how much the fans liked the slam dunk, and it became more common.

There are three types of dunks, there is the basic slam dunk ( http://www.youtube.com/watch?v=doIUo12kdGg ), the alley oop, which is when one player passes the ball to another player who is jumping and performs the catch and slam dunk while in air ( http://www.youtube.com/watch?v=1wdYk_thUEM ), and finally the standing dunk, which is when a player jumps straight up and performs a slam dunk ( http://www.youtube.com/watch?v=HMlQXOd2u_0 ).

With each slam dunk there is conservation of energy happening and there is a conversion of the kinetic energy the shooter has once he is leaving the ground and it is turned into gravity potential energy. Which means that applying the concepts learned in PMPM and  COEM, it is possible to figure out the speed I would need to perform the famous free throw line slam dunk ( http://www.youtube.com/watch?v=OD54eF2XKJA ).  

The 4.2 m/s is in the vertical component of the triangle because the energy bar graphs are analysing the vertical component of the system.

We are able to set Ek1 and Eg2 equal to each other because the speed of the jumper will be converted into gravity potential, and the total energy does not change.

The height used is 0.9 meters because that is the required height I would need to jump, I got this by taking the height i needed to get to and subtracting my height and vertical reach.

The horizontal component of the triangle gives us the speed I would need to be running at because, once I jump the horizontal component of my jump will be in constant velocity.

The physics of a curveball

The Physics of a Curveball

It was originally believed that a curveball was an optical illusion, Physicists were not able to explain why the ball would have a curved flight path. Although in 1671 Isaac Newton wrote a paper on the topic of the curved path of a ball with spin. The topic was later renewed in 1852, when Gustav Magnus performed an experiment with spinning objects moving through a liquid. He came to the conclusion that there is a force acting perpendicular to the initial velocity

Figure 1.

**Please ignore speech bubbles**  This diagram shows what Magnus’ finding was, that the reason a spinning ball had a curved path was because of the magnus force acting perpendicular to its motion.

Magnus Effect in Baseball

          When an object is moving through the air it comes into contact with a thin layer of air called the “boundary layer”. Since a baseball is not very aerodynamic the air peels away from the surface. This creates an area behind the ball where there is no air, which is called a “wake” which is a low pressure area behind it. The difference of pressures on the front of the ball and  the back creates air resistance and slows the ball’s forward motion. Although if the ball is spinning, the air and ball’s friction will cause the air around the ball to drag with the curve of the ball on one side and away from the ball on the other side. This results in an angled .Figure 2. 
Shows the effect of spin on the wake.

The ball has exerted a force of friction on the air, this force pulls the air down (using the bottom half of Figure 2.)  and because of Newton’s third law which is “for every action there is an equal and opposite reaction” this means that the air is exerting a force on the ball in the opposite direction which is the magnus force.

The stronger the magnus force is the more the ball will curve. The strength of the force is directly related to the rate of spin and the forward speed of the ball. Knowing this, Magnus was able to create the equation

Figure 3. 

Fm- Magnus force  

 S- Air resistance coefficient across the surface of the object                                                                                                                                                                                          

            W-Angular velocity vector of the object
            V-Velocity of the object

The discovery of the Magnus force has helped physicists understand the science of a curveball and overcome the myth that a curveball is not an optical illusion, but there is a force creating the curved flight path.


http://www.youtube.com/watch?NR=1&v=BTd5z6UI5_4&feature=endscreen (demonstration)
https://www.youtube.com/watch?v=23f1jvGUWJs (Video which demonstrates magnus effect well)

These videos both demonstrate the Magnus effect, the first video gives a demonstration of how wind on a non-spinning object alone does not create a Magnus force, but it takes the combination of wind and a spinning object to produce the Magnus force. As well, the second video provides a summary of some points covered in this post, as well it shows a demonstration which shows the Magnus force very well (rolling the paper off of the board).