Nicolas Léonard Sadi Carnot was a smart man who liked to figure out how things worked. He was also a French scientist who lived a really long time ago, like before your great great grandparents were even born.
One of the things that Nicolas was really interested in was how machines worked. He was particularly interested in heat and how it moved from one place to another. You know how sometimes when you touch a hot stove, your hand feels really hot? Well, Nicolas wanted to understand why that happened and how the heat could move from the stove to your hand.
So Nicolas did lots of experiments and observations to figure this out. And he discovered something really important that is called the "Carnot Cycle". It's like a set of instructions or steps that explain how heat can be used to power a machine.
Nicolas wrote a book about this called "Reflections on the Motive Power of Fire" and it was a big deal because it helped engineers and scientists understand how machines like engines and turbines worked. It was like he gave them a special key to unlock the mysteries of these machines and make them work more efficiently.
So even though Nicolas lived a long time ago, we still remember him today because of his important work on how heat can be used to power machines.