Deadly Gorge Bungee Design (Energy Practical)

After seeing many videos and images of other high school physics classes doing some variation of a bungee jump, we, fellow teacher Jeremy Smith and I, decided to implement one of our own.  This turned out to be a great way to wrap up our energy unit as students would be exposed to all three types of mechanical energy in this problem.  Our Deadly Gorge Bungee Jump Design was simple, it asked students to design a bungee jump that could work for a range of customers, in this case masses ranging from 100 g to 750 g.  Materials were limited to springs(we’re fortunate enough to have several sets of these that work great), string, and an adjustable ring stand.

IMG_1632It was really interesting to watch as the students got started right away.  Almost all of the groups began by simply playing with the materials, I often encourage this with new materials in class, just so students can learn on their own how they work.  Quickly following this initial play period was the adjust and check period.  There were no calculations being done, simply students writing down the height of the jump point and whether it hit the ground or didn’t come close enough.  I try not to step in too much with these types of problems, hoping that students will eventually apply the equations to the problem.  At the start of the next class period I helped the students talk through a conceptual understanding of the setup, including the variables and energy types.  This helped tremendously as groups started to work through the problem on paper.  About half of them had it, the other half just couldn’t get past the number of variables.  Those groups that struggled ended up coming to see me for some extra help and we talked through it together.

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On test day students chose one of 5 random masses and setup their jumps according to their calculations and testing.  Not all groups were successful on test day, with some groups dipping into the water, one group hitting the bottom, and a few just missing.  It was great to see their reactions and the groups that didn’t get it went immediately to figuring out why it didn’t work.

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This setup allowed groups to adjust one of three variables in order to be successful.  They could use a different spring, a different length of string, or adjust the height of the ring stand.  All three of these methods were employed in my class, the easiest adjustment though is simply to change the height of the ring stand according to calculations, this ends up being a quadratic with two solutions, one being negative.

One aspect of the problem that I’d like to quantify is the acceleration of the mass as it is slowed, as an actual bungee jump needs to do this smoothly so the customer doesn’t experience whiplash.

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Cart Races Lab Practical

I borrowed this idea that I originally saw from @rutherfordcasey and @kellyoshea.  I am always thinking about ways for students to collect data and to be able to assess their methods using that data.  So I decided to time the finish using two force plates, allowing us to quantify the race.  This turned out to be a rewarding lab practical midway through our Newton’s 2nd Law unit.

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The students received a fairly simple set of questions to guide them through the process and to give me something substantial enough to assess their understanding.

Newton’s 2nd Law

  1. Using the setup at the front of the room calculate where the two carts must start from in order to hit the force plate at the bottom of the ramps at the same time. The carts must travel a minimum of 1.0 m. Show all of your work in a neat and well organized manner below. You must provide some narrative to describe what you are solving for in each step.
  2. Test your calculations. How far off are you, is it within an acceptable amount of error?
  3. If the two carts do not hit at the same time, within an acceptable amount of error, re-evaluate your solution and perform the test again.
  4. What sources of error exist in this experiment so that your theoretical values do not match what actually happens?

In small groups the students worked through the solution and began testing.  They also learned how to measure the angle of an incline using a protractor and plumb bob.

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The 1.0 m minimum forced them to put more thought into the kinematics of the carts’ motion which was a great review of prior material.  After calculating and running their tests all groups were able to get great data, with the carts hitting within 0.10 s of each other.

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