Thomas woke up one morning and rubbed his eyes. The sun was already tickling through the blinds and from the kitchen came the aroma of mama's breakfast scrambled eggs. He jumped out of bed, slipped on his slippers and headed straight toward the scent. His faithful little dog Fifi, a small white terrier with cheerful black eyes, was already sitting by the kitchen door, impatiently wagging his tail. "Good morning, Fifi!" Thomas greeted and petted the dog behind the ears. "Woof!" Fifi replied, as if he wanted to say: "Finally you're up! A new day full of adventures awaits us!"
When they entered the kitchen, something caught Thomas's attention. On the pale floor tiles by the large window that led to the garden, small wet tracks were glistening. They were tiny, as if left there by some small creature. "Mama, look!" Thomas pointed. "We have a mysterious visitor here." Mama smiled. "Really? And who might that be?" Fifi curiously sniffed the tracks. He wagged his tail, then looked at Thomas with a question in his eyes. "It's not you, Fifi," Thomas said and looked at Fifi's dry paws. "Your paws are completely dry. And these tracks are so... strange."
The next morning the situation repeated itself. Again those same wet spots in the same place by the window. And on the third day too. Thomas couldn't sleep because of it. Who or what was making those mysterious wet tracks? "We must solve this mystery, Fifi," Thomas said determinedly. Fifi barked in agreement. First they checked all the doors and windows. They were firmly closed. No stranger could have gotten into the house. "Maybe a mouse?" Thomas thought aloud. But mice don't leave wet tracks, unless they had just been bathing in a water bowl, and that seemed very unlikely. Then he suspected Fifi. "Maybe you secretly drink water at night and then it drips from your chin when you go to the window," Thomas said and looked at the dog. Fifi just looked at him uncomprehendingly and whimpered, as if he felt wronged. Thomas immediately petted him. "Sorry, buddy, I know you wouldn't do that."
They decided to get up early the next morning and wait for the mysterious creator of the tracks. They woke up while it was still dark. Thomas quietly got up so as not to wake his parents, and Fifi followed him with perked ears. They sat in the corner of the kitchen, from where they had a good view of the window. They waited and waited. Outside it was slowly getting light. The kitchen was quiet, only the refrigerator occasionally hummed contentedly. And then Thomas spotted it. On the large window glass, tiny water droplets began to appear. First just a few, then more and more, as if the window was quietly crying. The droplets merged into larger ones and some began to flow down the glass. When they fell onto the windowsill and from there onto the floor, they created exactly the kind of wet spots they had seen every morning! "Aha!" Thomas whispered. "So no animal! The window is doing it!" Fifi curiously tilted his head and touched one wet spot on the floor with his paw. Then he licked his paw. "Woof!"
Thomas ran his finger along the fogged window. His whole finger was wet. "But why is the window doing this?" he wondered. "Why is it crying?" Just then mama entered the kitchen. "Good morning, my detectives," she smiled. "I see you're already on the trail of the mystery." "Mama, we've almost solved it!" Thomas exclaimed. "The wet tracks are made by the window! Look, it's all wet and water is flowing from it!" Mama looked at the window and then at Thomas. "Excellent, Thomas! You have great observation skills. And do you know why the window is wet?" Thomas shook his head. "No. That's another mystery."
Mama sat down at the table and Thomas with Fifi joined her. "Let's try to think about it," mama began. "When is it coldest outside? In the morning, right? And at night we heat our home, breathe, sometimes cook dinner or take showers. Then lots of warm and water vapor gets into the air in our house. You can't see it, it's like an invisible little cloud." Thomas listened carefully. Vapor? Like from a kettle when water boils? "Exactly," mama nodded, as if reading his thoughts. "Warm air can hold lots of this invisible water vapor. But what happens when this warm and moist air touches something cold? For example, our window, which is cold at night and in the morning because it's cold outside?" Thomas thought about it. "It cools down?" "Correct! And cold air can no longer hold as much water vapor as warm air. So that excess vapor turns back into water. Into small, tiny droplets. And those you see on the window. We call this phenomenon condensation, or simply fogging." "Ahhh!" Thomas exclaimed. "So those droplets are actually that invisible vapor that turned into water because the window is cold!"
"That's amazing!" Thomas said. "So it's not a mouse or mystery, but science!" He laughed. "And I was already thinking we had a water sprite at home." Fifi barked and wagged his tail, as if he too understood everything. Maybe he understood that the mystery was solved and his master was happy.
"Exactly, little scientist," mama smiled. "And you know what? We can show such condensation in another way too. Would you like to?" "Yes, of course!" Thomas exclaimed enthusiastically. He loved experiments. Mama took a clean glass from the shelf. "Now we'll pour cold water from the refrigerator into it and add a few ice cubes too, so it's really very cold." Thomas watched as mama filled the glass. Then they carefully placed it on the table in the warm kitchen. "And now we'll wait a little while and observe what happens to the outside of the glass," mama said.
At first nothing happened. The glass was just cold to the touch. But after a little while, Thomas noticed that the surface of the glass began to fog up slightly. Gradually, tiny droplets appeared on it, just like on the window! "Look, mama! The glass is fogging up too!" Thomas exclaimed and carefully ran his finger along the glass. His finger was wet. "Is this the same water from that invisible cloud in the air?" "Exactly," mama nodded. "The warm air in the kitchen touches the cold glass, cools down and the vapor in it turns into water. Just like on the window." Thomas was thrilled. "So those wet tracks weren't scary at all. They were just proof of how nature works! I have to tell Jake at kindergarten about this, he always thinks everything is ghosts." Fifi stood up on his hind legs and curiously sniffed the cold glass. Then he looked at Thomas and barked cheerfully, as if he wanted to say: "Great, we solved it together!" Thomas petted him. "Yes, Fifi, you helped too. You were a patient guardian."
"And have you ever noticed where else you can see such fogging?" asked mama. Thomas thought about it. "Well... when I take a shower and there's lots of hot steam, the bathroom mirror gets all fogged up! And sometimes the car windows too, when it's cold outside and there are several of us inside." "Excellent!" mama praised him. "Or when we breathe outside into the cold air in winter, steam comes from our mouths, right? That's also a similar phenomenon, except there we see the steam because it's very cold and it immediately changes into tiny droplets of water or ice. Even when you take a bottle of raspberry juice out of the fridge on a hot summer day, it will be wet on the outside in a mamaent." "That's so interesting!" said Thomas. "The world is full of such physical magic! I'm already looking forward to what new things I'll discover tomorrow. Maybe I'll find out why soap foams, or how airplanes fly!" mama smiled. "There are explanations for all of this. And the best part is that many of them we can explain and understand at home, with simple experiments."
Just then, Dad came into the kitchen, still a bit sleepy. "Good morning, why are you so cheerful and scientific here?" Thomas immediately ran to him. "Dad, Dad! We solved the mystery of the wet footprints! And I know what condensation is!" And with enthusiasm he began explaining to Dad everything he had learned about invisible vapor, the cold window, and the fogged glass. Dad listened with a smile and then patted Thomas appreciatively on the shoulder. "Well then, you're quite the great discoverer, Tommy! I'm proud of you." Thomas smiled from ear to ear. The mystery of the wet footprints was not only solved, but he had learned something new and amazing. And Fifi? He was already waiting impatiently by his bowl for his portion of breakfast scrambled eggs, looking forward to more adventures alongside his little, curious master. The world was one big playground full of questions waiting for answers. And Thomas knew that with a little thinking and curiosity, he could get to the bottom of many of them.