I have noticed that math texts often talk about the difficulty people have in understanding the concept of negative numbers. I always find this kind of statement odd. Negative numbers seem perfectly normal to me. And I know lots of little kids who are very comfortable with them. It occurs to me that this is a combination of climate and metric.
I live in Canada. In most of Canada, temperatures are below freezing for several months a year. In some parts of Canada, they are well below freezing. Even though something like 80% of the population lives within 200 miles of the US border, we still live pretty far north and pretty far from major bodies of water with warm currents that might moderate our climate. (The UK is further north but the Gulf Stream has a major impact on its climate.)
And we use the metric system. This means that the freezing point of water is 0. And all those months of “below freezing” means that we are using negative numbers in daily life to talk about the weather. We learn, as very small children, that a bigger number with a negative in front of it is colder. Many of us have thermometers just outside the window where we can check the temperature. It occurs to me that a thermometer is just a number line. Our kids are using number lines and dealing with negative numbers long before negative numbers ever appear in their math classes.
Now substantial swathes of the US have a similar climate to ours. The weather in Minneapolis is not significantly different from the weather in Winnipeg (at least to folks who don’t live out there). It’s cold. For several months. Even in the New England states, where it doesn’t get anywhere near as cold as Minneapolis, it is below freezing for several months. The thing is they use Fahrenheit. So despite the cold, it isn’t below zero (except in Minneapolis); or it isn’t below zero for as much of the winter. Negative numbers aren’t normal. They are probably associated with swearing about how &*(#& cold it is.
So, my top tip for all you Americans that have cold winters is to start using metric. Get a bilingual thermometer. Don’t bother to translate between F and C. You’ll quickly learn what various temperatures feel like. More importantly, your kids will get comfortable with negative numbers and the number line. Then when you teach pre-algebra and algebra, you can say “If it is -10 and it is going to get 15 degrees colder, will it be 5 or -25?” And they’ll get it. Believe me.
BTW, if anyone knows of any research on comprehension of negative numbers that might be used to test my hypothesis, do let me know.