When it's really cold out, you might think that a brisk run would be best to keep you warm on the way to where you're going. You produce more body heat when you run than when you walk, after all. But when you run, you create a wind chill that cools you down more than if you were walking. So which is it? Is it better to run or walk in the cold? Luckily, physics has the answer. Watch the video below to learn about it.