Alternate title: I think I’ll try/defining/Gravity (performed by Adele Dazeem)
Jason Chin‘s latest picture book, Gravity, caught my eye because it got dinged by a review in The Horn Book Magazine (May/June 2014) for simplifying the science “to the point of inaccuracy.” But let’s be honest, without an advanced understanding of calculus and physics, we’re all getting the simplified version of gravity.
“Everything has gravity,” writes Chin to his pre-K audience, prompting Roger Sutton to complain:
Despite the text’s assertion, objects, whether the sun or a banana, do not ‘have gravity’; they have mass (which affects gravity). And to say ‘without gravity, everything would float away’ misses the rather more essential point that without gravity there would be no anything to float anywhere.
According to Newton, gravity is a fundamental force that depends both on the mass of objects and distance between them. The more mass objects have, the greater the gravity; the farther apart they are, the weaker their attraction. Chin makes this connection for young readers by saying “massive things have more gravity” and drawing bold pictures of outer space that depict size* and scale in a really fun way. Now if gravity is a property of matter, and all objects have mass (which Sutton correctly points out they do), then surely they have gravity.
Einstein updated Newton’s definition by scrapping the idea of gravity as a force. Instead, his theory explains gravity as the distortion of space-time geometry in response to matter and energy. (For example, the topology of space-time around the sun dictates the earth’s orbit around it.) With this in mind, if Sutton wanted to criticize Gravity for the inaccuracy of the everything would float away line, he should have nitpicked that floating away implies force.
Instead, Sutton’s second assertion–that without gravity, nothing would exist–is more of a chicken-and-egg quibble. Matter and gravity are intrinsically related, but good luck proving causality.
It’s gutsy of Chin to tackle a tricky subject for a young age in such a vivid, memorable way. When I asked physicists with PhDs how they’d explain gravity to five-year-olds, they wouldn’t stop laughing.
*We all know size matters not, but for simplicity’s sake, let’s pretend mass and size have a positive relationship