Unit 8: Energy Storage and Transfer Model

Unit Intro:

The modeling materials introduce the idea of energy conceptually first, before jumping into the quantitative.  The teacher notes reference a Feynman lecture in which he uses an analogy to get at the idea of energy conservation (on Youtube here, starts at about 23 minutes).  Reading 1 in this unit uses a money analogy to get at the same idea–all energy is energy–it is just stored in different ways.

“What is energy?”  – We’ve essentially defined it as the ability to force something to move.  Working, then, is the actual transfer of energy.  We understanding, then, that the total amount of energy in a system is constant (unless energy has be added to or extracted from it), and working (or, more advanced, heating or radiating) is the mechanism by which energy is transferred (when a system changes how the energy is stored).

Quantitative Development

Hooke’s law lab, along with quantitative measurements of elastic energy being transferred to gravitational potential energy and kinetic energy, form the basis for the development of quantitative measures of energy as it is stored in various ways within a system.  The teacher notes provide good instructions on how to go about this whole process.  Our treatment was rushed, and developing these ideas as a whole class is not ideal.

2014-07-16 15.18.13

Reading:

Making Work Work – Gregg Swackhamer

Additional Resources:

Blog post on Energy Bar Graphs (LOL diagrams) from Kelly O’Shea.

Some examples of Energy Pie Charts, if you choose to use them.

PhET – Energy Skate Park

Lab Practica:

Lab practica for this unit are virtually limitless.  You might even ask them to revisit an earlier activity or practicum and use energy to analyze the system instead.

There is the classic “Barbie Bungee” activity in which students have to build a bungee cord (out of tied-together rubber bands) such that when Barbie bungee jumps, she gets as close to the ground as possible without hitting it.  It is a bit of a challenge, because when the length of the bungee cord changes, so does its spring constant.  A simpler option might be to extend the bungee cord with non-elastic cord rather than more rubber bands, in which case the spring constant wouldn’t change.

This past year, I allowed students to shoot me with water balloons using a sling shot (like the picture below).  They collected data about the sling shot and had to determine the launch velocity for a given stretch distance.  Then, using the projectile motion model and a predetermined launch angle, they determined the appropriate amount of stretch for the balloon to reach me.  Many of their calculations were pretty close, but several missed laterally that otherwise would have hit me.

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