A push from a hand is a convenient way to think about force, but does it make you think all forces are manual? (Photo by Valerie Everett )

I found a companion piece to last week’s musing on science from a child’s perspective. Entitled What College Physics Students Can Learn From Little Kids, it’s a revealing look at how fifth graders and college freshmen think about basic physics questions in the same incorrect way. The principles in questions are Newton’s laws of motion. Based on some simple, unguided observations, most students of both ages suppose that constant force is required for constant motion and objects left to their own devices will eventually come to a stop. Newton tells a very different story; constant force is associated with constant acceleration and objects not experiencing external force will keep doing what they are doing indefinitely–either moving with constant velocity or sitting at rest.

The article explores the implications for American junior high and high school education, since most students will have already encountered Newtonian dynamics multiple times between 5th grade and college yet they demonstrate little awareness or comprehension. I’m interested in a slightly different implication. The consistent wrong answers given by students of various ages and experience suggests a strong, common intuition about how things move. And it’s easy to see how that intuition might form. In every day life, things do slow down unless you keep pushing them: bicycles slow unless steadily pedaled, bumping into a table nudges it an inch but doesn’t send it into the wall, our own bodies only move if we constantly push off the ground with our feet. If science is supposed to be based on observations, why is Newton right when any child (or adult) can observe so many apparent counter-examples?

We see the forces that active agents like humans and animals create. What we fail to appreciate fully are the forces generated by “inanimate” objects. Those bikes and tables and people slow down not from lack of force, but from the presence of force exerted by the ground and the air–forces we call friction. Fully appreciating Newton’s physics starts by imagining a frictionless world far removed from daily experience. Visiting that imaginary place allows you to see that Newton’s laws actually do apply to our world and reveals those inanimate forces our minds find difficult to see.

Science may ultimately be about the real world, but we often have to imagine a world far from reality whose points of departure provide clarifying contrast. If using imagination to do science seems counter-intuitive, that’s OK; plenty of science is counter-intuitive. While a quick Google image search for intuition quotes returns nothing but inspirational messages about trusting your inner voice, your gut feelings, your truest self, the experiences of physics students clearly show that intuition can go wrong. In fact, science is useful precisely because it can show us where our intuition fails to align with reality. A counter-intuitive scientific theory like Newtonian dynamics isn’t wrong (or right) because it is counter-intuitive; it is useful if it corresponds in some way to reality. And if that theory tells us something out intuition never would, that’s great, because we have made a tool for understanding the world a little better than before.