In today's modern world, it's easy to take transportation for granted. The titles in the How Does It Work? series explain how vehicles stay on the go d can also stop when needed. Easy-to-understand text introduces the science and engineering behind these vehicles, while colorful, high-quality photos (some with parts labeled) show the vehicles in action. Following a brief introduction to density, buoyancy, and gravity, Hot Air Balloons tells how hot-air molecules make a balloon buoyant and rise and how hot-air-balloon pilots depend on wind currents to move. Each book comprises a graphic of the vehicle with labeled parts, sidebars with additional facts, a related activity, and a glossary. Connecting STEM with these high-interest topics makes this a winning series for young readers.