Wednesday, July 2, 2014

Barbie Zip Line

Inspiration from Matt, John, and Jedidiah helped me shape my Barbie Zip Line task today. Whenever I prepare new tasks for my students, I have been trying to keep mathematical modeling, student ownership/creativity, performance tasks, and openness in the back of my mind. That's a lot, right? Plus, there's a hundred other little things, but let's focus on the list above. As I reflect on today, I'll share how I would improve this for next time.

Supplies (in order of attachment):
  • Barbie doll, or an action figure like G.I. Joe, Superman, or Captain America
  • Velcro: One-wrap (don't get Sticky Back)
  • Carabiners
  • Swivel Spring Snap (optional)
  • Fixed Pulley
  • Rope (thin enough to fit through the pulley)
My first piece of advice after learning from today: don't skimp on the pulley system. I made two and I should have made (bought) more. I would spend the money and have enough pulley systems for the number of groups you plan on having. Second, you could connect the pulley straight to the carabiner and avoid using (buying) the swivel spring. Third, velcro (harness) is the best way to quickly attach your pulley system to the zip line rider.

Buy enough rope so that you can have lengths that are 10 feet apart. In other words, have different rope lengths: 30 ft., 40 ft., 50 ft., 60 ft., etc. This will play well into the mathematical modeling part of the task (see below). It will also help make it easier to get the pulley systems on and off of the zip line. Solving the task yourself will also help determine the rope lengths you'll need for your school site.

The task (handouts found here):
Depending where (and who) you teach, some students have been zip-lining before. Ask! It never hurts. Maybe they can share their experience. Plus, this gives you a chance, at some point (if you feel necessary), to talk about how they're sitting in front of you, ALIVE, because someone was able to do some solid math and build a sound enough structure for them to zip line on. Just sayin'.

I low-balled my students today on their budget. I should have raised it to $2500 or $3000. Figure out what will work for your site. However, this mistake allowed me to give some early finishers an extension: find a more reasonable starting budget.

Here are the opening costs of your zip line company:
Students had to receive approval from their Summer Academy principal by showing their designs. I highly encourage this move. Students see someone else taking a vested interest in their learning. The principal gets an informal glimpse of your classroom. And students have to be prepared to explain the math and their problem-solving approach. If your principal is unavailable, get someone else: teacher, custodian, campus security, etc. It could be you, but you're already doing the formative approval (assessment) in class.

All these prices can change depending on your tastes. I included a liability insurance just for fun. The materials for the harness and pulley system need to be of high quality, so don't make them cheap. $50 might have been too cheap. The most important material is the steel cable (rope). This will help create multiple solution strategies. It's beautiful. Overall, I was pleased with my price points.
I found that having students create three rides is essential to this task. At least three rides. Sometimes tasks generate such a strong focus on the ONE CORRECT WAY to construct an answer or problem-solve. This adds pressure and can rob students of discovering mistakes or playing around with numbers. By creating separate zip lines for both certain death and boredom (getting stuck), it does many beautiful things.

Students innately know what type of zip line would kill barbie: a steep zip line. They can sketch that on their whiteboard, no problem. On the flip side, students have a good understanding of a boring zip line: practically a horizontal line. They can also sketch that on their whiteboard. Both sketches can be done without using numbers, formulas, or mathematical notation. It creates an entry point for all students. So here's what they had to say:
Leyla: We have a chance to see what not to do.
Trevor: It reminds me of when we do Estimation [180] and you ask us to give a too low and too high. It helps us find a reasonable number in the middle.
Deena: It shows us what a wrong answer or zip line would be.
Students were able to draw steep zip lines, label the height 20 feet, guess the ground distance to be about 5 or 10 feet, and use the Pythagorean Theorem to calculate the length of the cable (hypotenuse).
Mathematical Modeling and Multiple Solutions:
Students were able to design their own zip line by playing around with the numbers between their certain-death zip line and boring zip line. I told them to dream big on the whiteboards as if money wasn't a factor right now. Most did. Most.

I had a couple groups first figure out the cost of all the materials ($700) and subtract it from the $1500 budget, giving their group $800 to spend on cable. With $20/foot, they could use 40 feet of cable for their zip line. They identified the height and the hypotenuse of the right triangle. Impressive.

One of these two groups felt this wasn't enough cable and it was still too steep. Michelle had been zip-lining in real life so she knew. This was my mistake, but it turned into an opportunity for me to extend this task. I asked them to create a new budget for me so the cable was longer, but within reason. If you need more of an extension, have them come up with a formula to determine the amount of cable and distance on the ground, given a specific amount of money.

Before they could go outside and test their zip line, students had to complete this list:
I had students transfer their work to their graph paper composition books before they took it to the principal. I'll insert some pictures:

Here's the permit:

It was a blast! Students loved it. Here's another extension:
Have students design a system that gets the pulleys and/or dolls back up to the top of the zip line.

[insert video here]

By the way, I did teach the Pythagorean Theorem in there somewhere. Where? You might ask. I don't remember: ALL throughout the task. Use discretion. Some students need it first. Some need it after you've let them mess around on the whiteboards.



  1. Love the use of whiteboard for the rough work. I need to do this more. Making this into a more engaging proposal with submitting your response along with a cost makes this a great task. Students are developing their argument, and doing the math to support their reasoning. Love it.

    Also, I agree on the materials. I found out from local hardware that if I give them enough prior notice they would actually donate some of the materials (next time). Also, I just goa standard roll of 200' of nylon rope from home improvement store. I look forward to the posting pics/videos when you get a chance. I had my students take pictures and video of the event and hashtag it so that I could go back and find the material later. This helped engage them a little bit more too.

    1. Thanks for your initial post, Jed. Thanks for stopping in too.

  2. Love it! I had a similar project where students had to submit proposals after playing around with some trial runs and creating a plan. I love the engagement that comes from this! I can imagine other questions that come out of this that involve other areas of mathematics that I will have to work a bit to tease out... A few things I will likely do with different classes (depending on course expectations):

    1. Students find prices for the cables. (In terms of making it more realistic, each foot would cost significantly less than your set amount... e.g.
    2. Need to consider how to involve quadratics in this for some courses... may leave out if it's too forced.
    3. Perhaps leave other items that riders need to buy for the students and give a bigger budget... helmet? other gear?? need to research zipline a bit more.

    This also inherently build other aspects to barbie bungee as well! I love how we're living vicariously through barbie.

    Thanks for sharing!

    1. Hi Jim,

      I definitely didn't make the time to research typical costs for materials and should have done so. Thanks for the link and suggestions of items like helmet. I'm curious how you could connect quadratics here, so please let me know if you find anything. If anything, I will have this task resurface when we discuss slope.
      Thanks for stopping in!

    2. Because the movement down the zipline is due to gravity then the distance vs time relationship will be quadratic. That is, Barbie will be accelerating down the zip line (at a rate smaller than free fall depending on the steepness). So if you change the activity to relate to having zip lines of different lengths and how the time changes then you hit quadratics. Note that this depends a lot on the steepness.

    3. Thanks for the tip, David. I'll be trying out Zip Line 2.0 this summer and will try to find a way to incorporate this. Thanks!

  3. Instead of Barbie, here's an alternative set of action figures to better represent the modern female. Just a thought, but it may also open up the task to storytelling and curriculum integration.

  4. Holy smokes! I love this! Totally using this next year. Thanks so much!

  5. Any video of you guys testing the lesson? Looks fun. I think they do this lesson at a local high school with them. Would be a nice culminating end of 8th grade year activity!

    1. I wish there were video. The video I recorded didn't pan out. I plan on doing it again this summer and will record and post here.

  6. I adapted and made this activity in French. My students liked to plan and construct this zip line. I created a video about that.
    Here is the video link :
    Here is a French adatation:
    Thank you for this excellent idea !

    1. Awesome! Thanks for sharing their experience!

  7. Mr. Stadel, first of all, my class LOVES your estimation 180... THANK YOU. Secondly, can you tell me how much time you allowed for this project? We're entering the land of linear equations next week and I'm so excited!!!
    -Carly Shellhammer (The New School, Fayetteville AR)

    1. Hi Carly,

      Thanks for your kind words. I ran this activity during the summer where we had longer class periods. I would plan for about 2 days worth of investigate and maybe a 3rd day of trial runs.