One of my favorite childhood reads bills itself as a geography museum in a book. In the introduction, it says that “education is basically a do-it-yourself activity. You can’t really learn something until you’ve held it, rattled it, smelled it, dropped it once or twice, and then, if it won’t kill you, taken a bite out of it.” To drive the point home, there’s a (fake) bite taken out of that very page. The book has spinners, activities, puzzles, a bag of real rice to illustrate global poverty, and not a single multiple choice question. (In case you’re wondering, it’s Earthsearch by John Cassidy, and I’m keeping my copy.)
One such exploit is walking the solar system. “Outer space is a Nothing whose dimensions completely boggle the mind,” it says. “It is a staggering lesson,” Earthsearch continues, “but you have to learn it through your feet. Your eyes cannot learn it. Don’t even try.” The ensuing activity involves representing the sun with a soccer ball. The book goes ahead and tells you the sizes and distances to the other planets; for example Pluto is a pinhead 1000 yards away. That’s great for conveying an initial understanding of just how big and empty the solar system is. (Actually, it’s even more empty, since you’re walking a line and the solar system is a sphere.) But for some reason I was never curious (as a kid) as to how they came up with the numbers. Or how such a small, distant object as that pinhead could be attracted by the sun. (Then again I never did the activity.) Point being the book explains neither proportions nor Kepler’s laws. Concepts are great, but at some point we need to buckle down, crunch numbers, and get The Right Answer.
We don’t need to derive calculus ourselves; we can stand on the shoulders of Newton who himself stood on giants. He’s more than happy to explain Pluto’s orbit (posthumously). Moreover, engineering – and we need engineers – is about building black boxes out of black boxes, and a there’s a certain amount of encapsulation involved. We have at most 20 years per person of education as a full-time job, a fact of both culture and neurology. It took at lot longer than 20 years to discover all human knowledge. We have to expedite the process.
So one one hand, if you’re a teacher who wants to do this activity with your students, do not force them to rederive proportions. Go ahead and give that lecture. But then have the kids figure out how far it should be. Break them into nine groups and assign each a planet (or Pluto – just because it’s not a planet doesn’t mean it doesn’t exist as part of the solar system). Give them – or measure, or have them look up – the diameter of the sun, the diameter of a soccer ball, and the sun-planet/Pluto distance. Then ask:
- What is the scale factor of our model? (How much smaller is a soccer ball than the sun?)
- How big should this planet be in the model?
- What household object can we use to represent this planet?
- How far away should this object be from the soccer ball?
Aggregate the class data, make a distinction between distance from the sun and distance from the last planet, and then walk the solar system. (You don’t have to walk to Proxima Centauri, some four thousand miles away.)
Just be careful that the don’t stumble upon the calculator designed for exactly this project, which is the first hit when googling “walk the solar system”. Well, such is the internet.