Rebroadcast: Happy Birthday, America! From the very beginning, science has shaped this country. Many of the Founding Fathers — Madison, Jefferson, Washington — were science geeks, and their methodical way of thinking is reflected in the Declaration of Independence.

To celebrate the holiday, we dig into the science that makes fireworks sparkle, flags durable, and hot dogs delicious. Plus, what brain researchers are learning about the pursuit of happiness and feelings of patriotism.