Field Goal! The Science Behind a Perfect Football Kick
AbstractDid you know that throwing, kicking, and punting a football all involve the science of projectile motion? A star NFL® quarterback, kicker, and punter each need to have a very good understanding of how a football moves through the air in order to help them win games. In this science project, you will set up a rubber band-powered catapult to represent a field goal kicker, and study how changing the distance from the goalposts affects how hard it is to accurately kick a field goal.
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Recommended Project Supplies
Use a rubber band catapult kit and a toy football to kick field goals and see how your success rate varies with distance.
Have you ever seen a National Football League (NFL®) game with an exciting, game-winning touchdown pass or field goal? Believe it or not, there is actually a good deal of physics behind those passes and kicks. The science of how an object (like a football) moves through the air when it is launched, kicked, or thrown is called projectile motion. Projectile motion tells you how forces like gravity and air resistance affect the path an object follows when it moves through the air, also called its trajectory. To land in a receiver's hands or pass through the field goalposts, the football needs to follow a specific trajectory, as shown in Figure 1.
Two different trajectories possible after kicking a football. When the football is kicked between the goalpost a black dotted line is used to draw the trajectory. When the football misses the goalpost a red dotted line is used to draw the trajectory.
Figure 1. A football needs to follow a certain trajectory for a player to make a successful field goal. To score points, the player must send the ball between the goalposts. If the ball does not go far enough (the kick is "short"), or if the ball goes to the left or right of the goalposts instead of between them (the kick is "wide"), then the field goal does not count.
However, not every pass or kick is perfect. It can be hard to concentrate when you have a 300 pound linebacker running at you full speed! There are many factors that can affect whether or not a field goal is good, including how the ball is held in place for the kicker, weather conditions like wind and rain, and how far the ball is from the goalposts. If you watch a lot of football, you have probably noticed some of these things. In this sports science project, you will test just one of these variables: distance. You will set up a rubber band-powered catapult to act like a kicker's leg, and use it to kick field goals with a small toy football. You will adjust the distance between the kicker and goalposts, and see how accurately you can kick field goals at each distance. How do you think your accuracy will change as you move farther and farther away?
Terms and Concepts
- Projectile motion
- Air resistance
- How does gravity affect a football (or other projectile) as it moves through the air?
- How does air resistance affect a football (or other projectile) as it moves through the air?
- What happens in real NFL games—are kickers more or less likely to miss when they attempt field goals from farther away?
- What do you think will happen to your field goal percentage as you move farther away in your experiment?
- Can you look up the kicking statistics for your favorite team's kicker? How many field goals do they attempt, and make, at different distances?
- Are there any limits on the trajectory of a real football? For example, what is the longest NFL field goal record?
Here are some additional references about the physics of football:
- Shipman, M. (2013, September 20). Wide left: study shows that holders play key role in field goal accuracy. Retrieved November 14, 2013.
You can use this page to look up statistics about different players and their field goal percentages at different distances:
- ESPN. (2013). NFL Player Kicking Statistics—2013. Retrieved November 11, 2013.
This is a general reference about projectile motion:
- The Physics Classroom. (n.d.). Projectile Motion. Retrieved October 29, 2013.
- Ping Pong Catapult Kit available from our partner Home Science Tools.
The kit includes:
- Catapult with easy to change settings
- Rubber bands (3, each 3 x 1/8 inch)
- Ping pong ball
- Plastic Wiffle® ball
- Clamp for attaching the catapult to some surfaces
- Optional, but recommended: C-clamp, at least 3 inch opening; available at a local hardware store or
- Note: The C-clamp will work better than the spring clamp that comes with the catapult kit for attaching the catapult to a wider variety of furniture.
- Sturdy piece of furniture, like a table or a desk, where you can clamp the catapult to the underside of the furniture, so it is hanging down like a kicker's leg. See the Procedure tab for pictures.
- Note: You need about 20 inches of clearance to operate the catapult in this position. Most normal desks and tables will provide plenty of space.
- Optional: Paper towels or a small dish towel. This is to use as padding if you do not want to scratch the furniture.
- Toy/party favor-sized football, about 3 inches long; available from a local party store or
- Important: These toy footballs are only about 3 inches long. Do not confuse them with child-sized game footballs, which can be over 6 inches long and are too big for this science project.
- If you do not want to spend extra money on a football, you can use the ping pong ball that comes with the kit.
- Something to use as a football kicking tee, like a medicine cup or small plastic bottle cap. You could also make one out of folded paper and tape.
- Small cardboard box or stack of books, to make sure the height of your kicking tee lines up with the height of your catapult (depends on the height of your furniture; see the procedure for details).
- Long, open area to launch footballs, like a long hallway or a back yard, preferably with at least 5 meters of clear space.
- You may need to temporarily move a piece of furniture to provide a clamping surface for the catapult. Be sure to get help from an adult if you need to move furniture around.
- Materials to construct a "goalpost", such as cardboard, scissors, and duct tape
- A medium-sized cardboard box, approximately 0.5 meters on each side, will work. See the Procedure for a picture of an example goalpost to get an idea of its size. The exact size of the goalpost is not essential for the science project.
- Tape measure, metric
- Lab notebook
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Set Up Your Experiment
- In this section, you will set up your experiment like the setup in Figure 2. Read the steps for detailed directions.
Figure 2. The experiment setup for this science project.
- Watch this video to learn how to set up your catapult. Note that in this project, you will mount your catapult upside-down.
- Set up your catapult.
- Get the catapult, metal pin, and a single rubber band from your catapult kit, as shown in the top left picture of Figure 3.
- Push the pin through the hole in the base of the catapult (the black part) to lock the circular metal disc in place, so the 45 on the disc is showing just below the black bar (see Figure 3, top right). Notice that the metal disc has multiple holes, so you have to push the pin through the correct hole to line up the 45.
- Note: This pin sets the "follow-through angle", or how far the catapult arm will keep moving after it makes contact with the ball. For this experiment, you will keep the follow-through angle constant. If you want to find out what happens when you change this angle, see the tab.
- There is a large hole in the top of the metal disc. Push a rubber band through this hole and hook it on both sides of the pin that sticks through the catapult's launch arm (see Figure 3, bottom left).
- When you are done, the assembled catapult should look like the bottom right image in Figure 3.
A catapult from xpult.com is assembled. A metal pin locks the radial disk in place, while rubber bands connect the metal arm to the radial disk on both sides. Now when the arm is pulled back the rubber bands will stretch and the radial disk will stay locked in place at a specific angle.
Figure 3. The catapult, rubber band, and pin (top left). Use the pin to lock the metal disc in place relative to the base of the catapult (top right). Loop a rubber band through the large hole in the metal disc, and hook it on both sides of the pin sticking through the launch arm (bottom left). The assembled catapult (bottom right).
- Clamp your catapult to a piece of furniture.
- Use a clamp (either the spring clamp that came with the catapult kit, or a C-clamp; a C-clamp will probably work better) to clamp your catapult hanging upside-down from a piece of furniture, like a table or a desk, as shown in Figure 4.
- Remember that you may need to move around some furniture in your house to have enough room for the experiment. Make sure you have at least 4 or 5 meters (m) of open space in front of the catapult.
- Note: In NFL games, distances are measured in English units: yards, feet, and inches. However, scientists always use metric units, so for your science project, you should always measure distances in meters.
- Important: If you do not watch to scratch the furniture, use paper towels or a small dish towel as padding between the furniture and the clamp.
Figure 4. Catapult clamped to the bottom edge of a workbench.
- Build your goalpost.
- Use household materials like cardboard and duct tape to build a goalpost that is roughly 0.3 m wide, like the one shown in Figure 5. The exact size of your goalpost does not matter for this science project; just make sure it is a reasonably sized target for your toy football.
Figure 5. This goalpost is made from cardboard, duct tape, and a small trash can.
- Set up your goalpost in front of your catapult.
- Set up your goalpost as far as possible from the catapult. When you do the experiment, you will start out at the farthest distance and gradually move the catapult closer.
- Ideally, you should set your goalpost up 5 m from the catapult. If you go much farther than that, you may go out of the catapult's range. If you do not have that much space available, you may need to start with the catapult closer.
- Set up your kicking tee.
- Use something like a medicine cup or a small bottle cap as a kicking tee (see Figure 6).
- Using a stack of cardboard boxes or books, as necessary, set up your kicking tee so the ball is at just the right height to be "kicked" by the end of your catapult arm when it swings (see Figure 7). The exact height of boxes/books that you need will depend on the height of the furniture you clamped your catapult to.
Figure 6. A medicine cup or small bottle cap will work as a kicking tee.
Figure 7. This picture shows a textbook and two cardboard boxes used to adjust the kicking tee to the appropriate height for the catapult.
Kick Some Field Goals!
- Make a data table like Table 1.
- Note: Depending on the amount of space you have to work with, you may have to adjust the distances in the first column. Try to make sure you test at least four different distances.
- For example, if you only have 4 m of total space, you could test distances of 1, 2, 3, and 4 m.
- If you have more space available, you could test 1, 2, 3, 4, 5, and 6 m.
- Note: Depending on the amount of space you have to work with, you may have to adjust the distances in the first column. Try to make sure you test at least four different distances.
|Distance (m)||Field Goals Made||Field Goal Attempts||Field Goal Percentage|
- Double check to make sure your goalpost is set up at the farthest distance from your data table. For example, if you are using an exact replica of Table 1, you should put your goalpost 5 m away from your catapult.
- Take some practice kicks to get used to using the catapult setup.
- Use one hand to pull the arm of the catapult back, while you carefully place the football in the kicking tee with your other hand.
- Move your free hand out of the way once you have placed the ball, so you do not hit your fingers!
- Let go of the catapult arm; it will immediately swing forward and hit the football. Did it go through the goalposts? If so, you scored a field goal!
- If the ball did not go through the goalposts, you may need to make some adjustments to your catapult setup. This part will take some trial and error, depending on how far off your first kick was. There are several different things you can try to help aim your kicks:
- If the ball did not go far enough (the kick was too weak), you can add more rubber bands to your catapult. Your catapult kit came with three rubber bands. Try adding one or two more rubber bands the same way you attached the first one. This will make each "kick" stronger.
- You can also adjust how far back you pull the catapult arm before releasing it. The farther back you pull the arm, the more it stretches the rubber band, so the harder it will kick the ball.
- If the ball is going too high or too low, try adjusting the height or the forward-backward position of your kicking tee slightly. This will change where, during the swing, the catapult comes into contact with the ball, which will affect how high or low it is kicked.
- If you are missing field goals wide left or wide right, try adjusting the left/right position of the tee slightly. This can affect whether the ball goes straight or hooks to the side.
- Once you have found a good setup to kick field goals, you need to record the settings you are using to make sure you can do repeated trials.
- Pay attention to how far back you pull the catapult arm. You can do this by reading the angle markings printed on the metal disc on the catapult. For all future trials, make sure you pull the catapult arm back to the same spot. This will ensure the ball always goes far enough.
- Pay very close attention to exactly where you place the kicking tee, as this can have a big impact on where the ball goes. It may help to tape down a piece of paper and draw a box around the kicking tee, to make sure you can put it back in the exact same place each time.
- If necessary, use duct tape to secure the pile that is holding up your kicking tee (for example, if you are using three cardboard boxes, tape them together so they do not shift around after each kick).
- When you have completed your practice kicks, take 25 official kicks to calculate your field goal percentage at this distance.
- Use your data table to record your total number of successful field goals and your total number of attempts.
- If you have time, you can collect more data and try more attempts (for example, 50 attempts at each distance).
- When you have completed all of your kick attempts at this distance, calculate your field goal percentage using Equation 1 and enter it in the third column of your data table:
- For example, if you attempted 25 field goals but only made 17 of them, your field goal percentage is:
- Move your goalposts to the next closest distance from your data table (for example, move them from 5 m to 4 m), then repeat steps 4–5 for this new distance.
- Do not change how hard you kick the ball. Keep the number of rubber bands and how far back you pull the catapult constant. Technically, this is different from real football (a kicker would not need to kick a 10-yard field goal as hard as they would need to kick a 60-yard field goal). But, since you are doing a controlled experiment, you want to make sure you do not introduce any extra variables.
- You can still take a couple practice kicks before you start taking data at the new distance.
- Remember to record the results in your data table.
- Make a graph of your data with field goal percentage on the vertical axis (y-axis) and kick distance on the horizontal axis (x-axis).
- If you need help creating a graph, you can use the Create a Graph website.
- Analyze your results. How does field goal percentage vary with kick distance? Did it get harder or easier to kick field goals as the goalposts got farther away? How do your results compare to your hypothesis?
For troubleshooting tips, please read our FAQ: Field Goal! The Science Behind a Perfect Football Kick.
Ask an Expert
- If you watch football games or play football yourself, you have probably noticed that real kickers follow through with their leg when they kick the ball. You can use the pin that locks the metal disc to the catapult's base to change the "follow-through" angle of the catapult arm. The pin determines where the catapult arm stops, which controls how far it will keep moving after it initially makes contact with the ball. Try a new experiment to measure how changing this angle affects your field goal percentage.
- Use a tape measure to measure how far the football goes when you:
- pull the catapult arm back to different angles
- change the follow-through angle (as described in the previous variation)
- use a different number of rubber bands.
- NFL kickers wear special shoes designed just for kicking. In this science project, you just used the cup at the end of the catapult arm as a "shoe." Explore how the size, shape, and material of the "shoe" affects the ball's trajectory. For example, what happens if you tape a flat piece of cardboard over the cup instead?
- What happens if you change the tee position? Create a science project to measure how the tee position affects the trajectory of the ball. Is there an optimal tee position to get the best field goal percentage?
Frequently Asked Questions (FAQ)
- You can rotate the entire catapult. This may be difficult to do if you have it clamped to a large piece of furniture like a table. You may have to ask an adult to help you rotate the entire table slightly.
- You can just move your goalposts to the left or to the right, as necessary. This may be easier than rotating the catapult itself, since the goalposts are smaller and lighter than a large piece of furniture.
- You can adjust the left-right position of the kicking tee slightly. Ideally, if you "kick" the ball dead-center, it will go straight. If you have already adjusted the aim of the catapult and the position of your goalposts, make sure that the catapult arm is impacting the center of the ball, and not hitting the sides.
If you like this project, you might enjoy exploring these related careers:
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