[intro]
Brrr, it’s really cold outside today! And wet!
I’ll have to put some salt out on the sidewalk so it doesn’t get all icy.
[Squeaks?]
That’s a good question!
You usually put salt on food —
so why would I be putting it on the sidewalk?
Well, why don’t we do an activity to find out, Squeaks?
You can help me figure out how to answer our question.
You, too! We can all learn more together.
So, Squeaks: If we want to figure out what salt does to cold, wet sidewalks,
what do you think we’ll need?
[Squeaks squeaks]
Got it! I’ll go grab some supplies and be right back.
Alright! Squeaks suggested I get two cups of water,
which sounds like a great plan to me.
I’m not going to do anything to this first cup of water,
but let’s pour some salt into this second one.
You might see big chunks of salt put out on sidewalks,
but the tiny pieces of salt from my shaker are the same thing,
just different sizes.
I’m going to set both of these cups in the freezer,
since the freezer is cold just like the weather outside today.
Then, Squeaks and I will go play for a little bit,
and we’ll come check on our water cups in a little while!
Whew, that was a good game of hide-and-seek!
It’s been about half an hour, and I just took the cups out of the freezer.
So, let’s see what’s going on!
Whoa, check it out.
The water with salt in it isn’t frozen,
but the water without salt has turned into ice!
[Squeaks?]
Oh, great question, Squeaks.
Squeaks wants to know where the water in our first cup went,
since it’s all turned to ice.
Well, they might not look the same, but ice and water are the same thing!
They’re both water, but in different states.
That means they look and act a little differently, even though they’re made of the same stuff.
What we normally call water is the liquid state,
which means it flows and sloshes around. Like in our second cup!
But when water gets really cold,
it freezes and turns into the solid state, called ice,
which is harder and frozen into one shape. Like in the first cup.
[Squeaks!]
Squeaks pointed out that it was really cold in the freezer!
So he wants to know why the water with salt in it didn’t freeze and turn into ice.
Well, normally, water freezes when it gets to be zero degrees Celsius,
or 32 degrees Fahrenheit.
That’s called its freezing point,
and it’s the special temperature where water can change state from a liquid to a solid,
and freeze into ice.
But the cool thing about salt is that it can make water’s freezing point even lower.
So that means, the water with salt in it needs to be
really, really, really, cold before it can turn into ice.
[Squeaks.]
Exactly!
When we took our cups of water out of the freezer,
both of them were probably around zero degrees Celsius.
So the cup with only water in it had frozen into solid ice,
but the cup with water and salt wasn’t cold enough yet! It would have needed to get even colder.
It’s just like the sidewalk!
When we put salt on a wet sidewalk, it lowers the freezing point of that water.
So when the temperature gets colder,
the water will have a harder time freezing into slippery ice.
[Squeaks.]
Ooh, that sounds like a good idea for an experiment, Squeaks.
Besides salt, what else can stop water from freezing,
or stop the sidewalk from getting so slippery?
Using salt on sidewalks can be great, but it does have its downsides.
Sometimes, the liquid water can carry the salt into streams and rivers,
which isn’t healthy for the things that live there.
So, maybe there’s something else that we can use instead of salt.
Like, I wonder what sugar would do, or even something like sand or rocks.
[Squeaks!] Good idea, Squeaks!
Squeaks is off to grab some supplies so we can test our ideas!
But you can try this experiment at home, too.
What do you think would work the best? We can’t wait to see what you find.
And if you’d like to keep learning and experimenting with Squeaks and me,
be sure to hit the subscribe button.
We’ll see you next time, here at The Fort!
[ outro ]