# Help! There’s no equation to use

Today the University of Waikato is hosting a group of local secondary physics teachers. We've had an entertaining morning, with some sharing of ideas. As part of this, Rob Torrens, who teaches our large first-year engineering papers, talked a bit about life as a first-year engineering student. How does the school to university transition work? (or not.) On a non-technical front, he talked about the need for students to begin to take some responsibility for their own learning. If you fail to submit an assignment, it might be a little while before it's noticed and acted on. At university there's no 'bell' to tell you that you need to be at your next lecture – there may indeed be no-one even telling you to get out of bed in the morning. It's easy fall off the radar if you're not motivated.

On a technical front, Rob talked about some of the skills developed at university that are new to many students. Mathematical modelling is one. He used the example of 'mass balance' in an industrial process. If you are drying grain, you put damp grain into your drier and extract dry grain from the end; this is achieved by drawing in dry air from outside, heating it up, passing it over the grain, and expelling the damp air. Mass balance says that mass isn't created or destroyed in the process. But how is that represented for this particular process. There isn't a 'grain-drying mass-balance' formula in most engineering text books. Students need to work it out for themselves. The mass of what goes in must equal the mass of what goes out, so:

M_grain_in + M_air_in = M_grain_out + M_air_out

We have an equation that we've constructed, just by thinking about the physical principles involved. Throw in some more consideration about the amount of water air can hold (and therefore what M_air_out – M_air_in can be, and we can find out useful things, like how much air we need to draw into the machine for each tonne of grain that goes through it. We've started the process of mathematical modelling.

This is a skill aligned well with what the Physics Scholarship exam is about – where students need to think carefully through physics concepts before drawing from mathematical equations.