Hey Squeaks, you sure seem like you're pondering that rubber duck.
Yeah, you're right.
No matter how long you leave it in the water, it always floats and never sinks.
Why do things float?
That's a really good question.
And we can make hypotheses or guesses about what things will float and what will sink.
That's what Jesse did with our friends Bill and Webb, remember?
Have you ever tossed some sticks into a pond?
Or maybe you like to bring a bunch of toys into the tub?
Either way, you've probably found that not all objects act the same when they're in the water.
Some things sink right to the bottom, while other things float on the top.
Why does that happen?
Well, I brought some friends to see if we can figure that out.
Hi, everyone.
My name's Webb, and... And hi, I'm his sister, Bill.
Since we live in a pond, we see a lot of things sink.
And a lot of things float.
I bet.
You know, you can actually learn a lot about something by seeing what it does in the water.
So I'd say this calls for an experiment.
First, we'll need a pretty big container of water.
We'll fill it about three-quarters full and set it up where it's okay if some splashes out.
Now we need some stuff to put in the water.
All kinds of different stuff.
We're gonna look for a couple things around the fort that are okay to get wet.
If you want to try this experiment at home, make sure you ask before you put anything from your house into the water.
Let's see what we found!
Alright, Squeaks found a penny, I found a stick and Bill and Webb.
They found two different spoons, a metal one and a plastic one.
Good job, guys!
Now, before we get started, let's take a closer look at what we'll be testing.
All of these things are made out of different materials, like metal, plastic, and wood.
Some of them are pretty small, and some are a little bit bigger.
I think we have a pretty good group of objects, because they're all pretty different.
Now, before we start putting things in the water, let's guess whether each one will sink or float.
And let's keep track of our guesses.
But how will we...
Great idea, Squeaks.
We'll use a chart.
All right, let's start with the stick.
Bill, Webb, what do you think?
Will it sink or float?
I can tell you guys are pretty excited.
Tell us what you're thinking.
Well, in the pond where we live, I've never seen sticks that have sunk.
Only ones that float.
Well, that's because you haven't seen the ones that have sunk.
Well, that's because they all float, Webb.
Okay, fine.
Put me and Bill down for the stick floats.
Okay, here we go.
And it floats!
Good job, you two!
Yay!
Next, let's try the metal spoon.
What do you think?
Will it sink or float?
I've never seen a spoon float.
Me neither.
Quack?
Quack, quack, quack.
We think it'll sink.
Okay.
Let's see.
It sinks.
Woo!
Yeah, we're the smartest ducks in the world.
Yeah.
Now, what about the plastic spoon?
Do you think it will sink or float?
Quack, quack.
Quack, quack.
Quack, quack.
Quack, quack.
Well, it's the same shape as the other spoon.
Yeah, and we think it might sink, just like the metal spoon did.
OK, let's see.
It floats!
Bummer.
That's okay, guys.
That's how we learn, right?
Yeah, I guess.
It's just weird.
The other spoon sank.
Well, let's record our results and see if we can find out why it sank after we test our next object.
Our next object will be the penny.
Do you think it will sink or float?
Hmm.
Well, a penny feels a lot like a metal spoon, so I think it'll sink.
All right.
And, Webb, what do you think?
Well, it's so light, but kind of small, and I don't usually see things that small floating.
I'll have to agree with my sister this time.
It's gonna sink.
It sinks!
Now that we've tested all of our objects, let's look at our chart.
Some of the objects floated, and some of them sank.
Let's see.
The metal spoon and the penny sank.
The plastic spoon and the stick floated.
Is there anything that's the same about the things that floated and the things that sank?
Well, we know that the metal thing sank, and the metal spoon feels kind of heavy.
But so does the stick.
And the stick floated while the spoon sank.
So maybe it's not all about how much something weighs or its shape?
You're right.
And that might help us explain why some things float and some things sink.
The answer has to do with something called density.
Everything, and I mean everything, is made of tiny particles that we can't see.
And how dense an object is depends on how much space is between those particles.
Particles?
Jessie, what the quack is a particle?
Now that's an awesome question!
Let's use our imaginations and pretend that particles are marbles.
We'll start with a bunch of marbles on a table.
If you had the marbles all right next to each other.
That's kind of how the particles would look inside an object that's dense, like the metal spoon.
But if those marbles were spaced really far apart, that'd be more like what the particles are like in something that's less dense, like the plastic spoon.
The metal spoon is more dense than the plastic spoon.
It's about the same size and shape, but the particles that make it up are closer together than the particles that make up the plastic one.
But remember, everything has density, including water.
What?!
It's true!
Since water has its own density, if something is more dense than the water it's in, it'll sink.
The metal spoon and the penny were more dense than the water, so they sank.
And the stick and the plastic spoon were less dense than the water, so they floated.
So will it sink or will it float?
It depends, in part, on density.
Hmm, you made some wrong guesses too?
Well, that's actually great.
It shows that you're thinking things through.
Eventually, Bill and Webb learned enough about sinking and floating to make a boat of their own.
Would you like to see how that went?
Hi, everyone.
If you haven't met us before, I'm Bill.
And I'm Webb.
We visited before on SciShow Kids, where we talked about things that sink and float.
That's right.
And today, we're going to experiment and make a boat that floats.
And we're going to test our boat to see how much it can hold before it sinks.
A friend of ours, the giant squid Stravaganza, once asked Jesse how boats can float.
And we learned that they float because of displacement.
Displacement is when an object displaces water, meaning that it moves water aside so it can take up that space.
A good example of this is when you get in the bathtub.
What happens?
Well, you get wet, yes, but also when you get in the tub, the water rises.
So you are displacing, or moving aside the water, which makes it rise up around you.
Hope you didn't get the floor wet, by the way.
But now that we've got our thinking caps on, let's make a boat.
What kind of boat should we make, Bill?
Well Webb, I always see people paddling around our pond in canoes, so I think we should make our own canoes.
Bill, for once, I've got to say, your idea is great.
They'll be the best canoes the world has ever seen.
Yeah, that sounds fun.
Let's get some help from our friends Sophie and Zane and get started.
I've got an idea of what we should use.
Aluminum foil, tape, and some scissors.
Is that it?
That's it.
Great.
And if you're going to use scissors like us, make sure you tell a grown-up.
Yep, safety first.
Let's start by cutting off a few pieces of foil that we'll use to make our canoes.
Now, take a piece of foil and bend it in the middle.
Then, let's shape the two ends and pinch them so that they point up.
You might need to use more foil and tape to get the shape you want.
You also want the two ends to be taller than the middle.
Yahoo, we finished our canoes.
Yeah, now it's time to test them out.
I mean, watching a boat is pretty awesome, but let's see how much they can hold before they sink.
To the tub.
OK, we're going to fill our boats with marbles until they each sink.
But you could use rocks, toys, or anything else that's OK to get wet.
I'll keep track of the number of marbles it takes to make each canoe sink.
All right.
Are you ready, Bill?
I'm ready, Webb.
Here we go.
Wow.
Look at it go.
Yee-haw.
Oh, man.
Is that one going to sink?
I think so.
I don't think that one's ever gonna sink.
Whoa.
Wow, can you believe it?
No way.
Oh no, boat down.
Oh no.
Oh man.
Let's check out our results.
One boat was able to hold 59 marbles and the other one held 101.
Okay, but Webb, I have a question.
What?
Why did our canoes sink?
I mean, we just told everybody that boats float because they displace water.
That's right.
They float as long as the amount of water the boat displaces weighs the same as the boat does.
Oh, I see.
When we started to make our canoe heavier, it began to sink a little lower into the water with each marble.
And each time it sank lower, it displaced or pushed aside just a little bit more water.
But when we put in that final marble, our canoe weighed more than the water that it could push aside.
And it sank!
You got it!
Yeah, Bill and Webb did do a great job with their boat.
Oh, an underwater boat?
You mean, like, a submarine?
It's kind of like a boat that can swim through the water, instead of floating on top of it.
You want to know more about how it works?
Really?
And then what happened?
That's great!
Squeaks was just telling me about a story he was reading.
It was about a submarine exploring the ocean.
You want to go on a submarine, too?
That sounds like it could be a lot of fun.
Maybe someday we could visit a submarine.
Actually, a viewer named Sam sent us a question about submarines not too long ago.
Submarines are kind of like boats, except they go under the water.
And Sam wanted to know more about how they do that.
And Squeaks does, too.
Well, submarines work because of the way things sink and float, and some really smart thinking.
You probably know that when you put things in water, some of them float to the top and some of them sink to the bottom.
We did an experiment to learn why things float or sink with our friends Bill and Webb.
Do you remember that, Squeaks?
We learned that whether something floats depends on its density, or how heavy it is for its size.
If it's heavier for its size than water, it sinks.
If it's lighter, it floats.
For example, a plastic spoon isn't very heavy for its size, so it floats.
But a metal spoon is pretty heavy for its size, so it sinks.
That's how boats float, too!
They're really heavy.
You wouldn't be able to just pick one up.
But they're not actually very heavy compared to how big they are.
They're not very dense, so they float.
And submarines can float on top of the water for the same reason.
But for a submarine to be able to go under the water it needs some of that really smart thinking I mentioned earlier.
To dive into the water, a submarine needs to become heavier for its size.
It needs to be more dense.
But it's not so easy to make something heavier when you're in the middle of the ocean.
That's why submarines have big tanks, called ballast tanks.
When it's time for the submarine to dive down, the ballast tanks open up so they fill with water.
Adding the weight of the water to the submarine makes it dense enough to sink.
You can see how this works if you have an empty bottle or jar and a bowl of water.
At first.
If you put the bottle or jar in the water, it will float, because the only thing inside it is air.
It's very light for its size, so it's not very dense.
But if you take the cap off and let the water in from the bowl, it will sink.
The water makes it heavier for its size, just like putting water into the ballast tanks on a submarine does.
The rest of the submarine is very strong and sealed up tight so water can't get in and so that if there are people on the submarine they can breathe.
To make sure they don't run out of air, they bring along extra air that's all squeezed together inside a bottle, like how you squeeze air into a bicycle tire when you pump it up.
And then they can go exploring under the water, just like the people in the story Squeaks was reading.
In real life, we use submarines for all kinds of things, including learning more about the oceans.
When scientists send submarines under the water, they find so many cool animals.
There are jellyfish, octopuses, crabs, fish, and tons of animals we've never even seen before.
But after the submarine is done exploring under the water, there's one more thing it needs to be able to do.
Maybe you've already guessed what it is.
We know how submarines dive under the water, but how do they get back up?
Well, remember how submarines bring along extra air?
If there are people on the submarine, they can use it to breathe.
But it's not only for breathing.
When it's time for the submarine to go back up to the surface, it pushes air into the ballast tanks and water out.
That makes the submarine lighter for its size, so it can float up to the top of the water.
It really is a very smart way of using science to explore the world!
Mm-hmm.
Squeaks observed, or noticed, that there are lots of ways to float.
For example, things can float in the air instead of water.
You just need a little science.
Like when you and Jesse made the magnets float.
Remember that?
Oh hi everyone!
You're just in time!
I've been working on some new experiments, and I'm so excited to show you my latest one.
I can make this ordinary magnet float in the air.
Thanks, Squeaks!
I'm excited, too!
Let's get started!
Alright, first, we take this marker and we stick it to the table.
I'm using some modeling clay to make it stick.
Next, I take one magnet ring and slide it down to the bottom of the marker.
Now, very carefully, I take the next magnet ring and lower it down the marker until…
Presto!
A floating magnet!
Squeaks, it's not exactly a magic trick.
It's more like a magnet trick, because magnets can do all sorts of amazing things.
Magnets are special objects made with metals.
I bet you have some in your classroom or your home, like maybe stuck to a refrigerator or whiteboard or in a toy.
And the important thing about magnets is they can make forces.
A force is a push or a pull, and magnets can push or pull on things made with many kinds of metal, like paperclips or nails.
That's why you sometimes see magnets stuck to refrigerators.
They can pull so hard on the metal inside the refrigerator that they'll stick to it.
We call things magnets pull on, like refrigerators, magnetic.
And get this!
Magnets don't even need to be touching something to push or pull on it.
That's one of the things that makes magnets so cool!
I agree.
Magnets are really fun to play with.
Now, testing to see if different things are magnetic can be fun by itself.
But really interesting things happen when you put two magnets together.
Check this out.
Sometimes the magnets pull on each other, so they stick together really hard.
But now look what happens when I flip this magnet over.
I can't push them together!
It's just like my floating magnet experiment.
The two magnets won't touch.
It almost feels like… they're pushing against each other.
Oh, good question, Squeaks!
Why does this happen?
Well, magnets have two sides.
We call them the North Pole and the South Pole.
Exactly, Squeaks!
It's a lot like the North and South Pole that you see on a map of the Earth.
In fact, Earth is a giant magnet!
But that's a different story, one we'll talk about soon.
When I hold the North Pole of one magnet and the South Pole of another magnet near each other, each magnet makes a really strong force and the two pull together.
We say that they attract each other.
They actually pull on each other pretty hard, so I'm being careful that they don't pinch my fingers.
Now, when I hold two north poles together, the opposite happens.
The magnets push against each other and won't stick.
In other words, we say that the magnets repel each other.
So different poles attract each other, and same poles repel each other.
Hey, maybe that's why they say opposites attract!
Oh, you've got it, Squeaks!
In my experiment, the two magnets on the marker are repelling each other.
This one has the North Pole facing up and this one has the North Pole facing down, so the two push against each other.
Right now, the side on the top is a South Pole.
So if I wanted to add another floating magnet ring, which side should I put facing the other magnets?
North or South?
South Pole?
Let's try it!
You were right!
Nice work, buddy!
The matching sides are facing each other, so the magnets repel each other and float.
You can use magnets to do all kinds of fun experiments.
You could try this floating magnet ring experiment at home, or try something new.
Maybe you could try attracting magnets to hold together sheets in a blanket fort.
Or you could try to balance things on repelling magnets.
Ah, Squeaks, that's a fun idea.
We could use magnets to put some art up on the fridge.
We could start our own magnet art gallery.
It is pretty amazing what you can do with magnets.
But do you know what I think the coolest way to float is?
It's floating in space, just like astronauts on the International Space Station.
Hey Sam, I've been looking for you.
I wanted to ask if I could use your telescope for a bit.
Sure, that sounds great.
I love using my telescope to look out into space, but today I'm looking at these pictures of people in space.
Living in space sure seems different than living on Earth.
There are people living on the International Space Station right now.
That's a big spaceship where people do experiments and learn about space.
I wonder what it's like there.
Wow, you're right.
It does seem different.
I mean, there's people hanging around in the air upside down.
That certainly doesn't happen here on Earth.
If you're a bat, it does.
But not if you're a human.
You definitely aren't upside down right now.
That sure would be fun to hang upside down so easily, though.
Whoa, what is that they're playing with?
That is water.
That's water?
It looks totally different than it does here on Earth.
I agree.
Water definitely doesn't float around in blobs here.
Wow!
Look at this!
They're hitting the water like a ball and it stays together.
It doesn't splash at all.
Things sure do behave weirdly in space.
You're right, things do behave differently in space than they do on Earth.
We can pretty much always count on things to behave a certain way here on Earth.
People don't ever float around, unless they're swimming, I guess.
But let's keep thinking about water.
Let's make a prediction, or guess.
What do you think would happen if we poured some of this water out on the table, Sam?
It would make a big mess.
That's what would happen.
The water would pour down and it would spread out everywhere, until it ran over the table and down onto the floor.
You're exactly right.
So I'm not going to make a mess right now.
But Sam, how did you know that would happen?
Hmm.
Well, I guess I knew that because that's what water always does.
It always spills.
That's right.
We can always count on water to do the same thing on Earth.
Hmm, this is starting to feel like a pattern, isn't it, Sam?
That's not all we can predict.
What if I poured water into a glass instead?
Uh, it would go into the glass.
Not just that, but it would become the same shape as the inside of the glass.
Watch.
Whoa, you're right.
I never thought about it, but the water doesn't really have a shape.
It's just shaped like whatever container it's in.
So what do you think the water would do in space?
Well...
I think if we poured water in space, it might float.
You're right.
I don't think that the water would even stay in the glass, would it?
It would probably just float right out of there.
And the water is more blob-shaped.
It can't really take the shape of its container when it's not in a container.
So, based on our observations so far, it seems like things also behave in a predictable pattern in space.
It's just a different pattern than you'd expect on Earth.
Yeah, in space, water doesn't seem to spread out.
It sticks together in a ball and it floats around.
Here, let me show you an even cooler example.
Wow, is that a candle burning?
That sure doesn't look like any fire I've ever seen.
Think back to the candles on a birthday cake.
What do those look like?
The flames on a birthday candle are pointy.
In space, they made a round ball.
But they've been pointy at every birthday party you've ever been to, right?
Your last birthday cake had a lot of candles, and all the flames were pretty pointy.
Um, you're right.
It was a lot.
In space, though, the flames are always round like that.
So we can still predict what fire will do, even though it's different.
Birthday parties on the space station must be pretty cool.
But what is it about space that makes these things act a different way from Earth?
Ooh, great question.
And this gives us a chance to answer a question that was sent in by one of our viewers.
It's because of gravity.
Eli, age 5, asks, what is gravity and how does it work?
What is gravity?
Great question!
Gravity is the force that pulls things down.
Actually, not down exactly.
The Earth pulls things toward its center.
That feels like down to us, because it's the direction we're being pulled.
Scientists are still trying to understand how gravity works exactly, but basically Everything has a little bit of gravity and it's pulling all the time.
Like when you drop something like a ball, instead of it just floating around in the air, it's pulled down to the ground.
We've already noticed that people don't just float around in the air on Earth.
And when you pour water out on the table, it spreads out over the table because it's being pulled down toward the floor.
This is all thanks to gravity.
The space station isn't that far from Earth.
Why doesn't the water on the space station act like it does on Earth?
Earth's gravity does pull on the space station, but the water on the space station acts differently because the space station and everything in it are moving very, very fast.
So fast that, even though it's being pulled down by Earth, it still keeps going around the Earth in a circle.
It's like it's always falling toward Earth, but never hits the ground.
Imagine if you poured a glass of water over a tall cliff.
Now imagine if there was no ground.
The water would keep falling forever.
If you could fall down with the water and watch it, it would seem like it was floating.
That was a great question, Eli.
It helped me understand living in space better.
Yep, we're used to things acting a certain way on Earth, and a lot of that is because of gravity.
People don't float around, water pours downward, even fire is pointy because of gravity.
In space, all those things are different.
But we can still observe what they do and predict or guess that a candle will burn in a ball or that water will float in a blob.
I'd love to play with water in space.
Those astronauts look like they're having so much fun.
I bet it would be a ton of fun.
But it's fun to look at space, too.
So can I borrow the telescope now?
Even though you have to go to space to float like an astronaut.
I love thinking about what it must be like.
Maybe some of you will be astronauts someday and you'll get to experience floating in space yourself.
But until then, if you want to keep learning with me Squeaks, Jesse and all of our friends, be sure to subscribe, and we'll see you next time here at the Fort.
