<ring> “Moire here.”
“Uncle Sy! Uncle Sy! It’s snowing! It’s snowing!”
“Yes, Teena, it started last night after you went to bed. But it’s real early now and I haven’t had breakfast yet. I’ll be over there in a little while and we can do snow stuff.”
“Yaaay! I’ll have breakfast, too. Mommie, can we have oatmeal with raisins?” <click>
<knock, knock> “Uncle Sy! You’re here! I wanna go sledding! Get my sled out, please?”
“G’morning, Sis. G’morning, Teena. Get your snowsuit and boots on, Sweetie. Want to come along, Sis? It’s a cold, dry snow, not much wind.”
“No, I’ll just stay warm and get the hot chocolate ready.”
“Bless you for that, Sis. OK, young’un, ready to go?”
“Ready! Pull me on the sled to the sledding hill, Uncle Sy!”
“Ooo, it’s so quiet. Why’s it always quiet when snow’s falling, Uncle Sy? Is the world holding its breath? And why is snow white? When I hold snow in my hand it melts and then it’s no-color.”
“Always the good questions. Actually, these two are related and they both have to do with the shape of snowflakes. Here, hold out your arm and let’s see if you can catch a few. No, don’t try to chase them, the breeze from your arm will blow them away. Just let them fall onto your arm. That’s right. Now look at them real close.”
“They’re all spiky, not flat and pretty like the ones in my picture book!”
“That’s because they grew fast in a really cold cloud and didn’t have time to develop evenly. You have to work slow to make something that’s really pretty.”
“But if they’re spiky like this they can’t lay down flat together and be cozy!”
“Ah, that’s the key. Fresh spiky snowflakes make fluffy snow, which is why skiers love it. See how the flakes puff into the air when I scuff my boot? Those tiny spikes break off easily and make it easy for a ski to glide over the surface. Your sled, too — you’ve grown so big I’d be hard-put to pull you over wet snow. That fluffiness is why <hushed voice> it’s so quiet now.”
“Shhh … <whispered> yeah … <back to full voice> Wait, how does fluffy make quiet?”
“Because sound waves … Have we talked about sound waves? I guess we haven’t. OK, clap your hands once.”
<CLAP!>
“Good. When your hands came together they pushed away the air molecules that were between them. Those molecules pushed on the next molecules and those pushed on the next ones on and on until they got to your ear and you heard the sound. Make sense?”
“Ye-aa-uh. Is the push-push-push the wave?”
“Exactly. OK, now imagine that a wave hits a wall or some packed-down icy snow. What will happen?”
“It’ll bounce off like my paddle-ball toy!”
“Smart girl. Now imagine that a wave hits fluffy snow.”
“Um … it’ll get all lost bouncing between all the spikes, right?”
“Perfect. That’s exactly what happens. Some of the wave is scattered by falling snowflakes and much of what’s left spreads into the snow on the ground. That doesn’t leave much sound energy for us to hear.”
“You said that snow’s white because of what snow does to sound, but look, it’s so bright I have to squint my eyes!”
“That’s not exactly what I said, I said they’re related. Hmm… ah! You know that ornament your Mommie has hanging in the kitchen window?”
“The fairy holding the glass jewel? Yeah, when the sunlight hits it there’s rainbows all over the room! I love that!”
“I do, too. White light like sunlight has all colors in it and that jewel splits the colors apart so you can see them. Well, suppose that jewel is surrounded by other jewels that can put the colors together again. Here’s a picture on my cellphone for a clue.”
“White goes to rainbow and back to white again … I’ll bet the snowflakes act like little jewels and bounce all the colors around but the light doesn’t get trapped and it comes out and we see the WHITE again! Right?”
“So right that we’re going home for hot chocolate.”
“Yaaay!”
~~ Rich Olcott
Hard Science Ain't Hard 