Hey guys!
Hey there, Squid!
How's it going?
TGS: Mmmph.
I’m kinda cranky right now.
Jessi: Oh no.
No one wants that.
What’s bothering you?
TGS: Cruise ships.
Jessi: Cruise ships?
TGS: Yeah, cruise ships.
You know, those giant boats that you people sail around in.
There’s been one floating above me all day, and I can’t get any sleep!
I mean, it’s huge!
And noisy!
It’s like a floating city!
So, instead of sleeping, I’ve just been bobbing awake, staring at it, and wondering.
How does a giant ship like that float on the water?
I mean, heavy things sink in water, right?
Like when someone up there tosses a rock into the ocean -- which happens, you know -- it
sinks.
So why does that heavy ship get to float?
Jessi: The reason a big, heavy ship like that can float has to do with its shape.
Whether an object sinks or floats to begin with has a lot to do with something called
displacement.
Displacement is when an object displaces, or pushes aside, water.
So, like, when you drop an ice cube into an already-full glass of water, some water spills
out.
TGS: That’s displacement?
Jessi: That’s right -- the amount of water that spills out is actually equal to the amount
of space the ice cube takes up!
Or think about when you take a bath.
TGS: Hold up.
Wait.
What’s a bath?
Jessi: Well, up here, we like to clean ourselves up by soaking in a tub full of nice warm,
soapy water.
TGS: That sounds gross!
Do that mean that humans just walk around all day getting dirty?
If you spent all of your time in the water like me, you’d never get dirty in the first
place.
Jessi: Well, not everyone’s the same, right?
I know some of the people watching here know what a bath is.
TGS: Mmmrph, okay.
Jessi: So, say you fill the bathtub up -- all the way to the top.
And then you climb in.
Now there’s water on the floor.
Lots of water.
The amount of water equal to the amount of space that you took up!
Now, one of the secrets to an object being able to float, is that it has to displace
enough water so that the water it pushes aside weighs as much as it does.
Alright, so, say you’re in the tub and you want to do an experiment.
You can bring in a small bowl, and some rocks from your rock collection.
If you put the bowl in the water, it’ll float.
Because the bottom of the bowl is displacing some water.
And the amount of water that it’s pushing aside weighs the same as the bowl.
Now, drop a little rock in there.
Add another, and another.
The bowl is getting heavier, so it’s sinking a little bit each time.
But even though the bowl is heavier, it’s also displacing more water -- so the amount
of water that it’s pushing aside still weighs the same as the bowl.
TGS: So what does that mean for the cruise ship?
Why doesn't it sink?
Jessi: Well, ships are designed to displace as much water as possible.
They’re realllly wide, and their bottoms tend stretch down really far, so they push
aside a lot of water.
Plus, a ship has lots of empty space inside it -- a lot of it is hollow -- which helps
to keep it light, compared to the huge amount of water that it’s displacing.
And voila... it floats.
TGS: OK, OK.
So that giant, noisy party over my head right now is displacing enough water that it can
float.
Well, you people may be noisy, but the fact that you figured out how to build giant metal
things that float… that’s pretty clever, I’ll give you that.
Jessi: Yeah, and I don't know about you, but some of my favorite things tend to clever
and noisy.
Thanks for joining Squid and me, learning about displacement.
See you next time!
TGS: Bon voyage!