Just the Right Size by Nicola Davies, illustrated by Neal Layton
c.2009, Candlewick Press
$14.99/$17 Canada
61 pages

What would it be like to be a superhero? What if you could fly through the air over your house, watching your neighborhood for criminals and saving everyone from danger? Imagine being able to crawl straight up the side of a building to look in a window, 80 floors up. Or think what would happen if you were 100 feet tall and could battle giant monsters.

What would it be like? It would be, like, impossible – as you’ll see in the new book Just the Right Size by Nicola Davies, illustrated by Neal Layton.

Have you ever wondered why most spiders are so small? Although some people would really hate it, why aren’t spiders gigantic, like in the movies? The reason is because of a “rule.”

Author Nicola Davies calls it the BTLT Rule, and it involves a little math: If you double the length of the spider, its surface area goes up four times, but its weight and volume go up eight times. That means that if a spider was the size of your house, his legs couldn’t support him and he’d collapse. What a mess!

The same rule applies for that little flying trip you wanted to take. Your muscles aren’t strong enough and you don’t have wings. Davies says the bigger you are, the harder it is to get airborne. Heavier also means bigger flappers are needed, which explains why dragonflies have such ginormous wings.

Okay, so let’s say you want to be like Spider-Man and crawl up the side of a building. In explanation, Davies looks at the feet of a gecko, which is a creature that can walk up a wall and across the ceiling with no problems.

Geckos have toes that are flat and spoon-shaped, and those toes are covered with thousands of tiny hairs that actually stick to microscopic portions of the ceiling. If you wanted the same kinds of toes, you’d better hope you have big shoes because your toes would have to be tens of thousands of times bigger than the gecko’s.

The BTLT Rule affects every creature underwater and in cold climates. Your ears and your lungs follow the BTLT Rule. The truth is, every living thing on Earth follows the rule, and it turns out that you are exactly as you’re supposed to be.

Just the Right Size took me aback at first. Davies initially tries to explain relatively complex mathematics in a kid-friendly way, but I thought it ended up being more confusing than not. It’s going to take a couple of readings and an adult to clarify, I think.

Once you get past that, though, everything makes perfect sense and the subject becomes more fun. The examples are easier for kids to relate to, and the illustrations by Layton make it even simpler.

If you’ve got a 9- to 12-year-old Spider-Man or Superman fan or mathematician, and you’re willing to help out a little, pick up this book. For beginners to this subject, Just the Right Size is just about the right size.

Terri Schlichenmeyer has been reading since she was three years old and never goes anywhere without a book. She lives on a hill in Wisconsin with two dogs and 11,000 books. Readers with questions or comments may write to her in care of this publication.