High in the sky, within one enormous grey cloud, it was as busy as an anthill. This was no ordinary cloud. It was a storm cloud named Rumble, and it was full of little water droplets and tiny bits of ice. One of the droplets, curious and as round as a little pearl, was called Droplet. Her best friends were sparkling, cheerful ice pals that everyone just called the Icelings.
“Catch me if you can!” laughed one of the Icelings, zipping past Droplet. The gusty wind inside Rumble the cloud spun them around like the best merry-go-round. They played tag, slid down the soft clouds, and cheerfully bumped into each other.
“Look out, here I come!” called Droplet and brushed against an Iceling who was tumbling head over heels. Suddenly, she felt a strange tickle. “Brrr, what was that? It tickled,” she giggled.
“Me too!” the Iceling joined in. “Every time I brush against you, I feel a strange tingling.”
They decided to investigate. They stood opposite each other. “Ready?” asked Droplet. “Now, let’s gently rub against each other.”
They moved closer with concentration, and the Iceling slid his icy body along Droplet’s watery side. And that’s when they saw it! A tiny, golden spark flew between them. It was so small that only the two of them could see it.
“Wow! Look at that!” Droplet exclaimed with delight. “Let’s do it again!”
They had no idea that their game was creating something called an electric charge. Every time they rubbed against each other, a little piece of this charge built up inside them. It was like collecting tiny little lights in an invisible pocket.
Soon, the other droplets and icelings noticed their fun game. “We want to make sparks too!” they called out, joining in. The entire cloud, Rumble, turned into one giant playground full of rubbing, bumping, and giggling. Sparks flew here and there, and the whole cloud began to quietly buzz and crackle.
“Children, children, be careful,” a deep, kind voice suddenly rumbled. It belonged to Rumble the cloud himself. He could feel more and more energy building up inside him. “You are playing beautifully, but soon you will have so much charge that it will no longer fit inside you.”
“And what will happen then?” asked Droplet, looking curiously at her friends. Everyone fell silent and listened.
“That charge will have to jump out somewhere,” Rumble explained calmly. “It’s like when you fill a glass with water. When it’s full, the water overflows. Your charge will find a way out in the form of one giant spark.”
Droplet and the Icelings looked at each other. A giant spark? That sounded exciting!
The rubbing continued, and Rumble the cloud grew darker and darker. He was so full of energy that his whole body felt tense. The droplets and icelings no longer felt just a tickle, but a strong buzzing sensation. “It’s coming soon,” Rumble whispered. “Get ready for the show!”
And then it happened. All the accumulated energy, all those billions of tiny sparks, merged into one. From the belly of Rumble the cloud, a dazzling, zigzagging streak of light shot toward the earth. It was the biggest and most beautiful spark they had ever seen. For a brief moment, it lit up the entire landscape below—the trees, the houses, and the fields.
“That was amazing!” Droplet cried out after the light faded. “That was the longest light-slide in the world!”
But right after the light show, something else happened.
BOOM! THUUUNDER!
The whole cloud trembled. A mighty roar rolled across the sky, and all the droplets and icelings huddled together in surprise.
“What… what was that noise?” one of the Icelings asked, a little scared.
Rumble the cloud laughed so hard that his whole body shook. “Don’t be afraid. That was just an echo of our big spark.”
“An echo?” they all wondered at once.
“That's right,” Rumble nodded. “That magnificent spark of yours, which we call lightning, is unbelievably hot. As it flew through the air, it heated it up so suddenly that the air shouted out loud in surprise. And that sound is what we call thunder.”
Droplet thought for a moment. “So thunder is really just the sound that lightning makes? Like when I clap my hands and it makes a sound?”
“Exactly, Droplet, you’re very clever!” Rumble praised her. “It’s just a much, much louder clap. And did you notice something interesting?”
“That we see the lightning first and only then hear the thunder?” an Iceling chimed in.
“Yes! And do you know why?” Rumble asked. They all shook their heads. “Because light is the greatest racer in the world. It is much faster than sound. While the slower sound of thunder is travelling to you, you have long since seen the fast light of the lightning.”
Suddenly, no one was scared anymore. They understood that lightning and thunder were just inseparable friends putting on a big show in the sky. One provided the light, and the other made a lot of noise to go with it.
“And what do you think, children?” Rumble’s voice called down toward the earth. “The next time there is a storm, try counting with your parents’ help how many seconds pass between the lightning and the thunder. You see the light right away, but the sound takes a while to travel. The higher you count, the farther away the storm is from you.”
Droplet and the Icelings smiled. The storm was no longer scary. It was just a big celestial game full of energy, light, and sound. And they were its main heroes. They cheerfully scurried across the cloud again, ready to gather charge for the next beautiful flash of lightning and its booming friend, thunder.