Just the Right Size: Why Big Animals Are Big and Little Animals Are Little by Nicola Davies, illustrated by Neal Layton. Grades 3-6. Candlewick, July 2009. Copy from my local library.
How come blue whales are huge and mice are tiny? Why can't humans lift 850 times their own weight like the rhinoceros beetle? Why don't giant monsters like King Kong actually exist? And why will humans never be able to walk on water or fly?
Just the Right Size answers all these questions and more in a very accessible way.
It all comes down to geometry, really. If a big object is two times the size of a smaller object, its volume and weight will be eight times the smaller object's. That's why large flying insects (like dragonflies) need much bigger wings than small flying insects (like gnats). And it also explains why big animals like whales eventually stopped getting bigger. The bigger an animal gets, the more food and air it needs. So if blue whales were twice as big as they currently are, there wouldn't be room inside their bodies for the huge lungs and digestive systems they would need.
The book takes a complicated question and explains it in a simple (but not patronizing) way. Plus, it's funny! And it has funny, cartoony illustrations! What more could you ask for?
Here's just one example of the humorous tone of the book:
"Once upon a time there was a giant who was just like a normal human, only ten times bigger all over: ten times taller, wider, and deeper, making him one thousand times heavier. The giant took his first giant step, and with a giant crashing sound, both his legs snapped. The end." (pg 24)
I just want to run out and hand this to every kid at my library. I think it's one of those books that kids might not know they're interested in until they actually start reading it, so it might need a little booktalking. But that should be easy since it's so funny and interesting. I'd venture to say that adults could learn something from Just the Right Size, too. I know I did!
Pair it with If You Hopped Like a Frog by David Schwartz for more great examples of relative strength and size.
Read more reviews at 100 Scope Notes and Carol's Corner.
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