# Skipping Science: An Experiment in Jump-Rope Lengths

An energetic activity from Science Buddies

ON THE ROPES: Think you're fleet afoot? Try this science challenge and you might learn a few tricks. Now, hop to it! Image: Image: George Retseck

Key concepts
Coordination
Endurance
Speed

Introduction
Have you ever wondered how you could do jump rope faster? The U.S. jump-rope record for the greatest number of jumps in one minute is 367! That's more than six jumps a second! How close do you think you can get to that number? What are some of the factors that will help you jump faster? One is the length of the jump rope!

Background
Jumping rope is great exercise. Professional boxers do it to improve their coordination and endurance. Plus, it can be a lot of fun! That's easy to see when watching students doing jump rope together, often competing for speed or tricks. And, there are official competitions for speed jumping. What would you do to improve your speed? The length of the jump rope can change how many jumps a person can make in a minute, but what length jump rope is ideal? The longer the jump rope the more time it takes to turn it in a full circle. The shorter the jump rope the faster it turns, but because the circle is smaller the jumper might have to jump higher to get over the jump rope, and that might slow the person down or cause him or her to make a mistake.

Materials
•     A three-meter (10-foot) jump rope
•     Two volunteers who know how to jump rope (including yourself)
•     Stopwatch or watch with a second hand
•     An open, flat space large enough for doing jump rope

Preparation
•     Choose an open, flat space that has enough room for doing jump rope. (Make sure nothing is nearby that you might bump into while you jump.)

Procedure
•     Fold the jump rope in half to find the midway point. Stand on this point with both feet. Put a handle in each hand and pull the handles straight up along your sides.
•     Shorten the rope by moving the handles halfway between your belly button and armpits, then tie knots in the rope just below the handles. This is the shortest jump-rope length you'll test.
•     Have the volunteer time you while you jump rope for one minute. As you jump, you or the person timing you should count how many jumps you do. When one minute is up, the person timing you should tell you to stop. If you "mess up" within the minute do not stop, but continue timing, jumping rope and counting the jumps. For example, if after 10 successful jumps, the rope hits your foot and you have to restart, the counter should count the next successful jump as number 11. How many successful jumps did you do in one minute using the shortest jump-rope length?
•     Readjust the rope length so that the tips of the handles are now just barely brushing your armpits. This is the medium length you'll test.
•     Again have the volunteer time you while you jump rope for one minute and count how many jumps you do in that minute. How many successful jumps did you do a minute using the medium length? Was it greater or less than the number of jumps you made using the shortest rope length?
•     Readjust the rope so that the tips of the handles just barely brush your chin. This is the longest length you'll test.
•     Again have the volunteer time you while you jump rope for one minute and count how many jumps you do during that period. How many successful jumps did you do per minute using the longest rope length? Was it greater than or less than the number of jumps you made using the shortest and medium lengths?
•     Switch places with the volunteer and have him or her repeat the activity so that now you will time and the volunteer will jump rope using the three different jump rope lengths. Was the same jump rope length the "best" one for both of you or did each person do better with different lengths? Was the same rope length the "worst" one for both of you?
•     Extra: Do this activity again, but this time count both the successful jumps and the number of times the jumper messes up. Did the rope length affect the number of mess-ups?
•     Extra: Listening to music may affect a person's jumping ability. Try doing jump 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?
•     Extra: Can jumping rope help you on a spelling test? Randomly assign volunteers to two groups: One group will not jump rope, but rather copy down 10 words from a spelling list with pen and paper. Members of the other group will jump rope and work with a partner who will call out from the list each word and its spelling first; the jumper will then repeat it, "jumping out" each letter of the word—one jump per letter. How well do the volunteers from each group spell the words the next day (using pen and paper)?

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