Skipping Science: An Experiment in Jump Rope Lengths
AbstractDid you know that the United States jump rope record (as of 2017) for the greatest number of jumps in a minute is 372? That's more than six jumps a second! How close do you think you can get to that number? If you are going to try to break the record, it might be important to figure out how jump rope length affects your success. Try your hand at this skipping science fair project and jump-start your chances for a jump rope record. If you have a smartphone available, you can use its accelerometer and a sensor app to measure how fast you jump.
Sandra Slutz, PhD, Science Buddies
Edited by Ben Finio, PhD, Science Buddies
This science fair project was inspired by this DragonflyTV podcast:
- TPT. (2006). Double Dutch by Francesca, Precious, and Marnicka. DragonflyTV, Twin Cities Public Television. Retrieved October 29, 2008.
Determine the best length for a jump rope.
Did you know that jumping rope is great exercise? Professional boxers do it to improve their coordination, which is the ability to make smooth and accurate movements involving different body parts, and to improve their endurance, which is the length of time for which someone can do a physical activity without stopping.
Plus, jumping rope can be a lot of fun! That's easy to see in the DragonflyTV video on the right, where Francesca, Precious, Marnicka, and their friends show off their double-Dutch skills while investigating the science of jumping rope. In double Dutch, there are two jump ropes being turned, by two people, while one or more people jump the ropes while doing tricks. One of the hard parts is knowing when the ropes are coming, which made Francesca, Precious, and Marnicka decide to investigate whether it was hearing the ropes or seeing the ropes that made them able to be successful at double Dutch. What do you think their experiment revealed? Watch the video to find out, and to see all their great jumping tricks!
In addition to jump rope tricks, there are also competitions for speed jumping. In 2017, the United States record for the most jumps per minute was 372! How many jumps per minute can you make? Do you think that the length of the jump rope might change how many jumps you could make in a minute? The longer the rope, the more time it takes to turn it in a full circle. Shorter ropes turn faster, but because the circle is smaller, you might have to jump higher to get over the rope, and that might slow you down or cause you to make a mistake. So, to help you get started on your own personal best jumps-per-minute count, in this science fair project you will determine the best jump rope length and get a scientific jump on your competition!
Terms and Concepts
Optional terms for students using a sensor to collect data:
- Why is jumping rope a good exercise?
- Why does it take more time to complete a full circle when swinging a long jump rope than a short jump rope?
This science fair project was inspired by this DragonflyTV podcast:
- TPT. (2006). Double Dutch by Francesca, Precious, and Marnicka. DragonflyTV, Twin Cities Public Television. Retrieved August 18, 2017.
This document shows US jump rope records in various categories:
- USA Jump Rope (2017). USA Jump Rope National Records. Retrieved November 4, 2020.
This website has more information about jump rope as exercise and how to perform different jump rope tricks and skills:
- Skip-Hop. (n.d.). Learning to Skip. Retrieved August 18, 2017.
For help creating graphs, try this website:
- National Center for Education Statistics. (n.d.). Create a Graph. Retrieved October 29, 2008.
Materials and Equipment
- Jump ropes (1 8-foot rope and 1 10-foot rope); available at sporting goods stores and available on Amazon.com
- Volunteers who know how to jump rope (3, including yourself)
- Lab notebook
- Graph paper
- With option 1 in procedure: Stopwatch or watch with a second hand
- With option 2 in procedure: Smartphone with a sensor app such as phyphox, available for free on Google Play for Android devices (version 4.0 or newer) or from the App Store for iOS devices (iOS 9.0 or newer). See the Option 2: Using the Sensor App section at the end of the procedure for instructions to use the phone in this project.
Note: In this project, you will determine what length jump rope allows people to jump the fastest by measuring their jumps per minute. There are two different methods to do this. In one method, you can have someone count your jumps using a stopwatch. In the second method, you can use a smartphone equipped with a sensor app to make a graph of your jumping motion, and count the number of peaks in the graph. You can find the instructions to do so in the Option 2: Using the Sensor App section.
Option 1: Using the Stopwatch
To start this project, you will need to find three people who know how to jump rope. You will each be jumping rope by yourselves—not double Dutch for this experiment.
- You can include yourself as one of the three people.
- If you or one of your friends would like to take part in the experiment but do not know how to jump rope, check out the resources in the Bibliography in the Background section for some methods you could use.
Fold the 8-foot-long jump rope in half to find the midway point. Have the jumper stand on this point with both feet, put a handle in each hand, and pull the handles straight up along his or her sides. Have a helper shorten the jump rope, using the following directions, until the handles are between the jumper's belly button and armpits. This is the short jump rope length.
- To make the jump rope shorter, the helper should tie knots just beneath the handles. Try to tie the same number of knots beneath each handle. Tie as many knots as needed to make the rope the right length.
- If the 8-foot jump rope is too short to reach midway between the jumper's belly button and armpits, use the 10-foot-long jump rope instead.
When the jump rope is at the right length and the jumper is ready to begin jumping, three things need to happen:
- The jumper should yell "Go!" and begin jumping.
- As soon as the jumper says "Go!", a second person should start the stopwatch.
- A third person should count the number of successful jumps over the rope the jumper makes.
The jumper should continue to jump rope for 1 minute, at which point the person with the stopwatch should yell "Stop!" so that the jumper and the counter both know to stop their tasks.
- If the jumper "messes up," the stopwatch should not stop. The jumper should continue jumping rope, time continues, and the person counting should keep counting up instead of restarting the count. For example, if after 10 successful jumps, the rope hits the jumper's foot and he or she has to restart, the counter should count the next successful jump as number 11.
- Record the number of successful jumps in a data table like Table 1 in your lab notebook.
|Short Jump Rope Length||Medium Jump Rope Length||Long Jump Rope Length|
|Trial #1||Trial #2||Trial #3||Average||Trial #1||Trial #2||Trial #3||Average||Trial #1||Trial #2||Trial #3||Average|
- Once the jumper has rested long enough to catch his or her breath, he or she should repeat steps 3–5 twice more for a total of three trials with that jump rope length.
- Using the same method as in step 2, re-adjust the jump rope length so that the tips of the handles are now just barely brushing the same jumper's armpits. This is the medium jump rope length.
- The jumper should repeat steps 3-6 using the medium jump rope length. Record the number of successful jumps in the data table.
- Now, using the same method as in step 2, re-adjust the jump rope length so that the tips of the handles just barely brush the jumper's chin. This is the long jump rope length.
- The jumper should repeat steps 3-6 using the long jump rope length. Record the number of successful jumps in the data table.
- Repeat the whole procedure (steps 2-11) for the other two jumpers. Remember to record the number of successful jumps in the data table.
For each jumper, calculate the average number of successful jumps for each jump rope length.
- For example, to calculate the average number of successful jumps that jumper #1 made using the short jump rope, add up the data for trial #1, trial #2, and trial #3, then divide by the total number of trials (which is 3).
Using the graph paper, make three bar graphs, one for each jumper, showing the average number of successful jumps for each jump rope length.
- Label each bar so you know what it represents.
- If you prefer to make your bar chart on the computer, try using Create a Graph.
- Look at your graphs. For each jumper, which jump rope length resulted in the most successful jumps over the rope in 1 minute? Which jump rope length was least successful? Was it the same for each jumper?
Option 2: Using the Sensor App
What if you wanted to take a more scientific measurement of your jumping motion? What could you measure? One thing scientists measure about moving objects is their velocity, or their speed and direction. When you jump up and down, your velocity changes over and over again as you slow down and speed up. Scientists describe this type of repetitive motion as periodic. A change in velocity is called acceleration. Sometimes it is easier to measure acceleration than velocity. Scientists measure acceleration using a device called an accelerometer. Accelerometers are built in to many smartphones and video game controllers to give them motion controls. They allow games to respond to motion when you tilt or shake the controller.
You can use sensor apps such as phyphox to record data with your phone's accelerometer. Try this procedure to find out how it works:
- Figure out how to mount the phone to your waist, hip, or torso while jumping rope. You could put the phone in your back pocket or use a phone belt clip. The phone should be tightly held to your body so it does not slide or bounce around.
- Open your sensor app. If you are using phyphox, select the acceleration with g sensor. Depending on how the phone is attached to your body, choose either the X or Y accelerometer graph to make it bigger. You want to measure up-and-down acceleration while you are jumping. So, for example, if the phone is vertical in your back pocket, you should use the Y accelerometer. If the phone is sideways in a belt clip, use the X accelerometer.
- Practice recording acceleration while jumping. Attach the phone to your body, press the play button in the phyphox app to start a recording (the phyphox app will automatically record all three accelerations simultaneously), jump rope for slightly more than a minute, detach the phone, and press the pause button to stop recording. Make sure to save your data.
- Review your data. It should look something like in Figure 1. In the phyphox app, you can zoom into your graph to remove any parts at the beginning or end of the recording when you were handling the phone. These parts of the data may look irregular or spiky on the graph. For your data analysis, you are only interested in the part in the middle when you were jumping, which should show a regular pattern like in Figure 1.
An example graph of acceleration over time while jumping rope has a very uniform pattern of steep spikes of positive and negative acceleration.
Figure 1. An example graph that shows data recorded with the phyphox app while jumping rope. The x-axis of the graph shows time in seconds and the y-axis shows acceleration in meters per second squared. Each peak in the graph indicates one jump. This graph shows 20 peaks in a 10 second period, so a total of 120 jumps per minute (20×6=120).
- Look at the graph of your acceleration. The graph should be periodic (the same pattern repeats over and over). Each repetition of the same pattern, or period, represents one complete jump. If you count the number of peaks that occur in one minute on the graph, that will tell you how many times you jumped in one minute. You may see smaller bumps or flat parts in the graph if you messed up and had to start over. Only count complete jumps.
- If it is too difficult to count the number of peaks in a one-minute graph, try recording data for a shorter amount of time. For example, you can record for 10 seconds, count the peaks, and then multiply by 6 to calculate the equivalent number of jumps per minute.
- Once you have practiced recording data while jumping rope and counting the number of jumps using the graph, follow the same procedure described in the "Option 1" section of this experiment. However, use the graph recorded with your sensor app for each trial to count the number of jumps per minute, instead of having a helper use a stopwatch.
Ask an Expert
- Does jump rope length also affect the number of mess-ups? Keep track of both the successful jumps and the misses and plot them both. Are the two numbers related? Hint: a fourth person may be needed to keep track of the number of mess-ups.
- Also try this experiment using different jump rope tricks, instead of just plain jumps over the rope. Does length have more of an effect on tricks than on plain jumps?
- Design an experiment to find the best jump rope length for double Dutch.
- In the DragonflyTV video in the Introduction, Francesca, Precious, and Marnicka jumped rope to different music with different beats. Try jumping rope to slow music, fast music, and no music. Does the music change how many successful jumps you can make in a minute? How about the number of successful jumps you can make in a row without messing up?
- Can jumping rope help you on a spelling test? Randomly assign volunteers to two groups: One group will copy down 10 words from a spelling list with pen and paper. The other group will work with a partner who will call out the word and the spelling first, and then the jumper will repeat the word and each letter back and "jump out" each letter of the words—one jump for each letter. Test your volunteers the next day with the spelling list (have them spell out with pen and paper each word that they practiced the day before) and see which group has the best scores, on average.
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