None of these pieces really present positives about desalination -- can you find some more resources that explain how desalination works and in what circumstances it makes sense to do it?

Is there a way to filter by domain? I'm trying to use hypothes.is in a high school class to get students to annotate pages on my own site. I can't count on them to use consistent tagging, but if I could filter all annotations from my entire domain I could get a useful stream of the students' work.

Why is there a non-convertible kinetic energy?

Because momentum is conserved. If there was a net momentum before an interaction, there must still be a net momentum after, and that implies that there will still be some kinetic energy after, no matter what happened during the collision.

$$\begin{eqnarray} v_f & = & v_i + at \\ t & = & \frac{v_f - v_i}{a}\\ \Delta x & = & v_i (\frac{v_f - v_i}{a}) + \frac{1}{2}a(\frac{v_f - v_i}{a})^2 \\ a\Delta x & = & v_i v_f - v_i^2 + \frac{1}{2}(v_f^2 - 2v_fv_i + v_i^2)\\ a\Delta x & = & \frac{1}{2}v_f^2 -\frac{1}{2}v_i^2 \\ v_f^2 - v_i^2 & = & 2a\Delta x \end{eqnarray} $$

The experiment in question involved dropping a block of wood onto a nail that was partially driven into a block of styrofoam. We manipulated the mass of the block and the height of the block, and measured the depth the nail was driven into the block as the responding variable.

We found, in general, that the response was linear for both manipulated variables, though the data was quite noisy. Here we are trying to understand what we should expect the result to be.