[intro]
I know right? That was so weird! I wonder if… Oh, hi! Squeaks and I just got
back from a nature walk! And we saw the strangest thing:
a tree branch that looked like it was growing white hair!
We took some pictures—see? It looks just like hair!
We decided we wanted to investigate it further, so we carefully took a branch back to The Fort.
We were going to look at it under the microscope and maybe run some tests on it.
But by the time we got back, the hair had turned into this liquid!
Anyhow, we just asked The Fort’s supercomputer to figure out what we found.
And we were just waiting for the results... [Ding!]
Perfect timing! Aha! What we found was actually ice!
And That’s why it melted! [Squeaks agrees]
Apparently, this kind of ice is super rare. It only appears when conditions are just right.
And it forms because of a special property of water: it’s stickiness!
[Squeaks squeaks] You’re right, Squeaks—water doesn’t
feel as sticky to us as stuff like honey. But it really likes to stick to itself.
If we could look at water really closely, we would see that it’s made of tiny, identical pieces.
And these pieces like to stick to each other — kind of like magnets!
And we can actually see this.
Watch what happens when I add drops of water to each other on top of this penny.
See how the water makes a sort of bubble shape?
The water is sticking to itself so strongly that it doesn’t spill over the sides!
Scientists don’t call this stickiness, though.
When a liquid sticks to itself like this, they call it cohesion!
If we try the same thing with another liquid, like rubbing alcohol…
you can see it doesn’t make that dome.
That’s because the alcohol doesn’t have the same cohesion as water does.
[Squeaks squeaks]
Ah, yes Squeaks!
What does cohesion have to do with that icy hair we saw?
Well, it turns out cohesion is a big part of why the ice forms that way.
You see, the tree branches the hair ice was growing on have water inside them.
That’s because, if you were to look inside a tree,
you would find a bunch of little tubes that carry water and nutrients all around.
And some of these tubes connect to the outside of the tree,
making little holes that you can see with a microscope.
Now, when the branch breaks off the tree, these tubes can fill up with rainwater.
when the air around the branches begins to get cold,
the water at the very edges of these tiny holes starts to freeze.
And when water starts to freeze, it gets bigger—
because all those tiny pieces of water
arrange themselves into a special pattern called a crystal,
and this pattern takes up way more space than regular, liquid water.
And since the ice needs room, it moves to the outside of the branch.
Knowing that, what do you think happens to the liquid water that’s still
in the tube as that frozen part grows?
[Squeaks squeaks]
Let’s think about it this way:
We said that the pieces that make up water stick to each other.
What would happen if a group of friends were in a line holding hands next to a doorway...and
the first friend went through the door?
[Squeaks answers]
Right! The first friend would pull on the next person in line
so that they ended up next to the door!
[Squeaks squeaks Yes, good job, Squeaks!
As the frozen water goes out into the air,
the next bit of water gets pulled right up to the edge of the hole!
And it gets pulled there because of cohesion. Then that water freezes and goes out of the hole.
This keeps happening over and over again….
until there’s a long, thin hair of ice!
And since they were just super thin ice strands,
the when we brought it inside was more than enough to melt them.
[Squeaks squeaks]
Ooo that’s a good question! What do you think would happen if we took this water
and put it outside? Would it become hairs again?
[Squeaks squeaks] You’re right. If
we froze this water again, it would just make regular ice, not hair ice
since it’s not in that branch anymore, so it doesn’t have those holes to grow out of.
[ ding-noise] Oooo look at this, Squeaks!
Thanks to cohesion, ice can grow into some other pretty spectacular shapes.
If water freezes in holes in dirt much in the same way it does in branches that grow hair ice,
you can get ice needles.
And if it happens through long thin cracks in plant stems, you get frost flowers!
We were really lucky to see this today, Squeaks!
[Squeaks makes a suggestion]
That’s a great idea—I bet Mister Brown would love to see our pictures.
Let’s go show them to him!
Thanks for joining us on SciShow Kids!
If you want to keep learning with us here at The Fort, don’t forget to hit the Subscribe button!
[ outro ]