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Kicking a Curve Ball: The Cause of a Soccer Ball Curving in Flight

science fair
by

Jordan Alvarez

on 30 December 2013

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Transcript of Kicking a Curve Ball: The Cause of a Soccer Ball Curving in Flight

Kicking a Curve Ball: The Cause of a Soccer Ball Curving When Kicked By: Kailie Dugger and Jordan Alvarez 1st Hour Mrs. Gazda November 11, 2012 Abstract The purpose of the experiment is to understand what makes a soccer ball curve, so that kicking curve balls can be replicated by athletes everywhere. The procedures used consisted mainly of kicking a soccer ball using a machine made of two supports, PVC pipe, and a soccer cleat. To evaluate the curve of the ball, a video camera recorded each kick at five different positions. The ball’s position shifted .75” to the right for each test. To measure the curve, the ball was kicked in each position softly so that the angle of the kick could be found. Then it was kicked with a harder force to initiate curve. On the computer, a grid was put over the videos’ frames to accurately determine the curve of the ball in each trial. The average curve of the ball was -18” when it was hit 0” off center, -26.6” when it was hit .75” off center, 13.2” when it was hit 1.5” off center, 10.8” when it was 2.25” off center, and 30.8” when it was 3” off center. In conclusion, the hypothesis was supported because the farther from the center the ball was kicked, for the most part, the ball's curve was also larger. Question How is a curve created to the path of a kicked soccer ball? Background Research When research began, there were any number of topics that were of interest, such as gender affecting color preference, heart rates during different emotions, and even lasers drilling holes in ice. Eventually it was narrowed down to topics that had to do with soccer, such as why the follow through is so important for strong kicks, what causes some soccer players to score more frequently than others, and what caused the soccer ball to curve when kicked. The last question was developed after looking around on the Internet and discovering a video on "Creating Spin or Swerve in Soccer Shots(Wilson)" that focuses specifically on creating “swerve on the ball” by “think(ing) of the soccer ball as having an equator.” When kicked on the left along the equator with the outside of a right foot, the ball will swerve to the right. This was a major finding because it was the first indication that the spot the ball is hit at can cause it to change directions. To find if curve worked the same way when the ball is hit at a different spot or with a differently positioned foot, the article "How to Curve a Ball" was confided in. It stated that professional soccer player Roberto Carlos knew how to make curved kicks by “hitting it (the ball) at a particular velocity and with a particular spin.” This offered two more hypotheses to help answer the question of what causes a soccer ball to curve. It also introduced the concept of the Magnus Effect, which became the next research topic. The website "The Physics of Soccer(Miller)" stated that “there are four forces that take place in order for this shot to work: force of the kick(velocity), drag, gravity, (and) Magnus Force.” It stated there had to be a force behind the kick, but that drag – being air resistance - would act upon it to slow it down. Then it teaches that “Magnus Force is caused when there is pressure on both sides of an object moving through the air or a fluid.” Less pressure on one side will cause the ball to turn that way. The book "Sports Science Projects: The Physics of Balls in Motion(Goodstein)" helped to explain that “As a ball spins through the air, a force develops that is greater on one side than the other.” This is Magnus Effect. Even the book "Baseball Miscellany(Silverman)" stated that balls curve when pitchers put “force on one side of the baseball to generate topspin. This creates an area of low pressure on the side of the ball with no force on it.” This sparked the idea that the same was possible in soccer, but instead of throwing, kicking could cause topspin and such. Then, however, a new thought occurred: perhaps the air pressure in the ball affected how much Magnus Force was acting on the ball. The website"How Does the Air Pressure of the Soccer Ball Affect the Distance it Travels When Kicked? Materials Materials continued ... Experimental Design Procedures Building the Kicking Machine Written Results Discussion Further Study Works Cited Data * Hypothesis: The location on the ball that it is kicked at will cause it to curve.
* Hypothesis Statement: If the location the ball is kicked at is farther away from the center, then the ball will have a larger curve, because kicks near the side of the ball cause the force to go around the ball rather than through it.
* Independent Variable: The location on the ball that it is kicked at.
* Levels: Every .75 inch across the middle. There is 0”, .75”, 1.5”, 2.25”, and 3” away from the center of the center of the ball.
*Dependent Variable: The curve of the ball’s path.
*Constants: The machine used to kick the ball; the person operating the machine; the air pressure in the ball; the ball used in the experiment; the cleat; the camera; The placements of the machine, camera, and cone in the middle of the goal; The program used to make the grid; the speed the cleat hits the ball * (2) Sawhorses (27 ½" Tall)
* (2) PVC Pipes (1 ½” Diameter; 6 Feet in Length)
* (2) T-connecting PVC Pieces (2”Diameter)
* (1) T-connecting PVC Piece (1 ½ " Diameter)
* (2) PVC Pipe Bearings (1 ½ " Diameter; 2” Length)
* (4) 0.5” diameter x 2” Bolts
* (4) 0.5” diameter Nuts
* (1) Size 5 Soccer Ball
* (1) Size 10 Left Soccer Cleat
* (1) Bag of Concrete Mix
* (Approximately 1) Cup of Water
* (1) Hacksaw
* (1) Electric Drill and Bit * (1) Pencil
* (1) 1 ¼” Diameter O-Ring
* (1) 48” by 8” Board of Wood (VERY thin)
* (1) Bottle of Gorilla Glue
* (2) Large Free Weights of 35lbs
* (2) Large Free weights of 45lbs
* (1) Photoshop Program
* (1) Cone
* (1) Tape Measure
* (1) Recording Camera on approximately 3 ½ ft high
Tripod Books:
Goodstein, Madeline P. "The Magnus Effect." Sports Science Projects: The Physics of Balls in Motion. Berkeley Heights, NJ: Enslow, 1999. 50-53. Print.

Silverman, Matthew. "How Does A Curveball Curve?" Baseball Miscellany: Everything You Always Wanted to Know about Baseball. New York, NY: Skyhorse Pub., 2011. 7-11. Print.

Internet Sources:
"Air Pressure." Air Pressure. Clouds R Us, n.d. Web. 5 Oct. 2012. <http://www.rcn27.dial.pipex.com/cloudsrus/pressure.html>.

"How to Curve a Soccer Ball." How to Curve a Soccer Ball. Ultimate Soccer Coaching, n.d. Web. 1 Oct. 2012. <http://www.ultimatesoccercoaching.com/soccer-kick/how-to-curve-a-soccer-ball.html>.

"Kicking a Soccer Ball - Pro Tips and Techniques." Kicking a Soccer Ball - Pro Tips an Techniques. Soccer-Training-Methods, n.d. Web. 8 Oct. 2012. <http://www.soccer-training-methods.com/kicking-a-soccer-ball.html>. Works Cited continued... Mendelson, Kenneth. "Ask a Physicist Answers." Ask a Physicist Answers. Physics Central, 2012. Web. 8 Oct. 2012. <http://www.physicscentral.com/experiment/askaphysicist/physics-answer.cfm?uid=20091123102747>.

Miller, Ben. "The Physics Of Soccer." The Physics Of Soccer. Slideshare, 19 Dec. 2009. Web. 1 Oct. 2012. <http://www.slideshare.net/dodrums/the-physics-of-soccer>.

Parrish, Rogue. "How Does the Air Pressure of a Soccer Ball Affect the Distance It Goes When Kicked?" LIVESTRONG.COM. N.p., 26 May 2011. Web. 5 Oct. 2012. <http://www.livestrong.com/article/412822-how-does-the-air-pressure-of-a-soccer-ball-affect-the-distance-it-goes-when-kicked/>. Works Cited continued... "Why Do Footballs/soccer Balls Curve?" Yahoo! UK & Ireland Answers. Yahoo Answers, Mar. 2012. Web. 1 Oct. 2012.
<http://uk.answers.yahoo.com/question/index?qid=20120222120828AA60FIp>.

Wilson, Mark. "Creating Spin or Swerve in Soccer Shots." EHow. Demand Media, 24 June 2008. Web. 1 Oct. 2012. <http://www.ehow.com/video_2360370_creating-spin-swerve-soccer-shots.html>.

DVD:
Really Bend It Like Beckham. Dir. Russell Thomas. Prod. Andrew Higgie. Perf. David Beckham. Capital Entertainment Enterprises, 2004. DVD. 1. Place the two sawhorses so that the top boards of wood are 45” apart.
2. Using the hacksaw, cut the PVC pipes into three pieces with the lengths of 24”.
3. Mix 3 cups of concrete mixture with 1 cup of water.
4. Fill the cleat with the water and concrete mixture
5. While the concrete is still wet, stick the one 24” piece of PVC pipe in the concrete with the pipe leaning on the heel of the cleat.
6. Allow the concrete at least one hour to harden.
7. While the concrete hardens, use the drill to drill a hole 0.5 " in diameter into one side of one of the 2” diameter T-connecting pieces. With the T-connecting piece laying on the opposite side that the hole will enter, drill the hole 1 ½” inward from one of the outer edges, and also directly in the middle of that side.
8. With the drill, proceed to drill another .5” hole 1 ½” inward from the opposite outer edge and directly in the middle of that side of the same T-connecting piece used in the previous step.
9. Repeat steps 7 and 8 on the other 2” diameter T-connecting piece.
10. With the drill, drill two more .5” diameter holes into the top of each sawhorse. The holes should be the same distance apart as they are on the T-connecting pieces and equidistant from the outside edges and the sides of the top board. Procedures Building the Kicking Machine 11. Place one of the T-connecting pieces on one of the sawhorses, aligning the holes of the sawhorse with the holes on the T-connecting piece.
12. Use the bolts 0.5 " in diameter to thread through the holes on the sawhorse and T-connecting piece. Go from underneath and thread them upwards so that the end protrudes from the hole on the inside of the T-connecting piece.
13. Tighten nuts on the end of the bolts that are protruding inside the T-connecting piece.
14. Repeat steps 11-13 with the other sawhorse and 2” diameter T-connecting piece.
15. Take the other two 24” PVC pipes and put one PVC bearing of 1 ½" diameter onto each of the PVC pipes. It does not matter which side of each pipe the bearing goes on.
16. On the same PVC pipes used in step 15, attach the ends WITHOUT bearings together by pushing them in opposite openings of the longer tube on the 1 ½” diameter T-connecting piece.
17. Take the two PVC pipes that are now connected by the 1 ½” diameter T-connecting piece, and put the ends with bearing in the T-connecting pieces that are attached to the sawhorses. It should cross from sawhorse to sawhorse like a bridge. They should be loose enough to spin easily inside the 2 ½” T-connecting pieces. Procedures Building the Kicking Machine 18. If the concrete is dry, cover approximately 2 inches of the end of the pipe opposite the cleat in Gorilla Glue.
19. Quickly place the gluey end in the last opening on the 1 ½” T-connecting piece, making sure that the cleat is perpendicular to the pipes that cross from one sawhorse to another, and that the laces are facing frontwards so that they may be able to hit a ball between the two sawhorses.
20. Place one 45lb weight on the front of each sawhorse.
21. Lay the 48” by 8” board of wood on the ground underneath the cleat, and position yourself to face the machine.
22. Lay the 1 ¼” diameter O-Ring directly in front of the cleat.
23. Use a pencil to trace the inside of the O-Ring.
24. Shift the center of the ring .75” to the left, and trace it.
25. Repeat step 24 three more times.
26. Set the 35lb weights on the ground on each side of the board to prevent the board from moving. continued ... continued ... Data Data continued ... continued ... Data continued ... Cleat Filled with Cement O-Ring Used to Mark Location of the Ball and Hold in Place Kicking Machine Kicked Ball Captured in Flight Photo with Grid Showing Curve Trajectory The results state that when the ball is hit on the outermost point, it will curve more than when hit in the center. The average curve of the ball was -18” when it was hit 0” off center. When hit at 0.75”off center, -26.6” was the average curve. At 1.5” off center, the ball had an average curve of -13.2”. The average curve was 10.8” when kicked at 2.25” off center. The average curve was 30.8” when it was hit at 3” off center. A pattern wasn't apparent until the second test (.75" off center) and after. The pattern after the second test was that as the distance away from the center of the ball increased, so did the amount of inches the ball curved to the right. The trend was that there was a positive correlation. Background Research continued ... After all the trials, the leg was spun as fast as possible. When doing this, it was was observed that there was more curve. To further the understanding, a new machine could be built that will accurately and consistently test the curve by changing its speed. It is already known that it will curve when hit on the side, so the new hypothesis statement could be, if the leg kicks the ball faster, then there will be more curve, because the speed transfers more force to the ball. Performing the Experiment 1. Set a cone directly in the middle of the back of the goal. Set up the kicking machine the way that it looked at the end of the procedures for “Building the Machine”.
2. Make sure that the pipe with the cleat is straight out from the middle of the goal/the cone. Place the machine approximately twenty yards away from the front of the goal.
3. Set up the video camera on the tripod about 6 feet behind the machine, so that it is in line with the cone and the cleat.
4. Turn the camera on.
5. Place the O-Ring back on the pencil outline that is directly in front of the cleat.
6. Set the ball on the O-Ring.
7. Pull the pipe with the cleat back so that it is parallel with the tops of the sawhorses.
8. Hit the record button on the camera.
9. Release the leg, allowing it to swing forward and hit the ball.
10. When the ball stops rolling, stop recording on the camera.
11. Repeat steps 5-10 nine more times.
12. Repeat steps 5-10 ten more times but this time place the O-Ring on the pencil outlining that is .75” off center.
13. Repeat steps 5-10 ten times for each of the rest of O-Ring outlines that are on the wooden board. This becomes the soft kick that will later be extrapolated. continued ... Procedures continued ... 14. Repeat steps 5-10 with the O-Ring on the original spot in front of the cleat, but this time hold the pipe with the cleat perpendicular to the tops of the sawhorses, and drop it so that the cleat swings through and hits the ball like it did previously.
15. Repeat steps 5-10 with the cleat perpendicular to the tops of the sawhorses ten times for every O-Ring outline on the wooden board. This represents the curve of the ball’s path.
16. Paste the first video onto the Photoshop program and place a grid over it so that there are 24 vertical lines going down between the two back goal posts, and twelve smaller vertical lines between each of those 12 lines. Every vertical line is an inch.
17. Use the program to draw an extrapolated line from the ball down the path that it was taking, all the way to the bar that lays across the back of the goal.
18. Count over to see which vertical line the extrapolated line crosses. If it is to the left of the cone, then it is a negative number, and if it is right, it is positive. Record that data in a table.
19. Repeat steps 16-18 for all of the videos that measure angle (so when the cleat was parallel to the tops of the sawhorses).
20. Repeat steps 16-18 for all of the videos that measure the curve (so when the cleat was perpendicular to the tops of the sawhorses). Record this data in a different data table.
21. Create a new table.
22. Subtract the information from Test 1, Trial 1 for measuring angle from Test 1, Trial 1 for measuring curve. The answer to the subtraction is the actual curve of the ball for Test 1, Trial 1. Record the answer in the new table.
23. Repeat step 22 for every corresponding test and trial until the new table is full. Procedures Performing the Experiment In conclusion, the results show that the curve of the ball’s path is affected by the spot that the ball is kicked at. Even though the first test and the second test had a negative correlation, the rest of the tests had a positive correlation, which ultimately allows the thought that the second test was flawed in some way, and that if it had not been, the results may have had a completely positive correlation. Basically, starting at the second trial and above, the farther away from the center that the ball was kicked, the larger the curve of the ball’s path was, and this was what was expected aside from the first trial having a negative correlation to the second. A valid explanation for this could be that the when the ball was kicked on the side, more force went around the ball on that side than it would when it was kicked straight on. When kicked straight on, then the force mostly just pushed the ball forward, but when kicked on the side, the force traveled around the ball.
The hypothesis statement states that if the location the ball is kicked at is farther away from the center, then the ball will have a larger curve, because kicks near the side cause the force to go around the ball Discussion rather than through it. It was supported because the curve of the ball’s path did increase as the distance from the center of the ball increased, despite the second test which may have been affected by an error.
The experiment could be flawed because when the ball was placed in front of the cleat, it may not have been directly in front of the cleat, it may have been off by a few millimeters. And if it was, then the pipes that acted as bridges across the sawhorses may have shifted farther right of the center of the ball, taking the cleat with them, and causing the cleat to hit the ball towards the left, which would cause a slight negative angle, rather than no angle or even a slight positive angle as expected. The ground also may not have been perfectly flat, which may have caused the ball to bump slightly to one side when it was rolling across the ground, but this problem was mostly taken care of by using the slow motion on the computer to monitor the angle of the curve and eliminate the bumps in its path by creating the extrapolated line before the ball starts rolling across the bumpy ground.
The experiment could be improved by performing on a flat surface/more level field to ensure that an angle wasn’t thrown off by a bump. Also, if the machine produced even stronger kicks then the results may have been more drastic and more accurate. Every hard kick has angular effect and curve effect. The angular effect (the soft kick) must be subtracted from the kicks with both angle and curve (the hard kick) to get the effect of just the curve. Therefore, we take the average soft kick for test #1 and subtract it from the average hard kick for test #1, and so on for all of the tests. (Parrish)" helped to understand that this probably wasn't the case because air pressure mostly affects the distance that a ball sails. “Your kick transfers more energy to a stiff ball, compared to a spongy one, as less of the energy is lost to the deformation of the ball’s surface,” the cite says. It also introduced the idea of atmospheric pressure having an effect on the ball: “A ball kicked at altitude in Mexico City, for example, travels further than a ball kicked at sea level in Miami Beach”. The article "Air Pressure" helped to further clarify atmospheric and air pressure. “If we travel up a mountain or go up in a hot air balloon, for example, the air pressure gets less the higher we go.” This however, did not seem to apply to a ball’s curvature, so to check already gathered information, "Why Do Footballs/Soccer Balls Curve?“ explained that a ball curves because of the direction that it spins. "The layer of air that tou(c)hes the right hand side of the ball will move faster because the ball is also turning in that direction …whereas the layer of air touching the left hand side of the ball moves slower.” It continues to tell that the left side of the ball moves slower because the air on that side is going against the direction that the ball is spinning. The ball will ultimately curve in the direction that is it spinning more quickly towards. The website "Ask a Physicist Answers(Mendelson)" introduces that "If the ball is kicked directly in line with its center of mass, it will not spin. An off center kick will cause it to spin.” Reassessing this statement helped to develop a new hypothesis: the spot that the ball is kicked at causes it to curve. Then research decided what position the foot of our kicker should be in to get the most power. The website "Kicking a Soccer Ball - Pro Tips and Techniques" led to the idea that getting power "includes a big wind up, and a big follow through using the top of your foot for the shot.” It explained different positions that the foot could be in for different situations, but this was the position chosen to help get power behind the kick. Then the movie "Bend it Like Beckham" – David Beckham being a professional soccer player famous for his curved shots – taught to hit the ball “off center with the front inside of the foot” to get curve. That foot position became a constant and the place on the ball that it is kicked at became the independent variable in the experiment. continued ...
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