Oh wow, look at that!
Look at those big red bubbles.
Looks beautiful doesn't it, mama?
This is a home-made lava lamp. It's a bit different
to the ones you buy in a shop
but it works in a similar way.
In the glass here I've got oil and water
with red food colouring in it. To get the lava lamp effect you just drop
pieces of alka-seltzer tablet into the glass.
The alka-seltzer reacts with the water at the bottom to create bubbles of gas.
Because the bubbles are less dense than both the oil and the water,
they float to the top.
When the bubbles burst at the top, the water sinks back down,
which is what gives us this circulating effect.
It's a great make just on its own,
but you can also use it as part of a slightly longer activity
investigating floating and sinking.
So what do you think we're going to do with all this stuff today?
Put it into the water, and see what happens?
So, let's try...
Tomato!
Floating or sinking?
It's sunk and it's turning around and making a different colour.
This one's smaller, what do you think this one's going to do?
I don't know let's see.
Oh, but they're both spoons...
It's because this one's a bit lighter and it's made of plastic.
Ah, okay.
And this one is made of metal and metal is really heavy.
Viola's right that the metal spoon is heavier in the plastic one,
but it's not always the case that light things float and heavy thing sink.
Otherwise ships and boats wouldn't float.
Whether or not an object floats depends on its density,
and that depends on its mass and its volume.
The mass of an object is a measure of how much stuff it contains.
The volume is a measure of how much space it takes up.
The density of an object is defined as the mass of the object
divided by its volume.
If something is more dense than water, it will sink. If it's less dense, it will float.
Using tinfoil is a really great way to explore the idea of density in more detail.
With the same size piece of foil, we can scrunch it up into a larger ball
and it floats on the water, but if we really squish it down
it will sink. You might have to have a bit of a bash at it first, though.
So this is the same bit of foil, and we've really squashed it. What do you think...
Sinks!
Did you think it was going to sink or did you think it was going to float?
Sink!
Did you? Why did you think you it was gonna sink? Because it was squashed all together,
And what were we squashing out?
Water.
Yes, there was water. What else?
Air.
Viola what would you like to drop in next? The big fruit!
I'm not going to drop it.
It floats! I thought it might sink!
Why did you think it might sink?
Because it's really heavy!
If we peel the skin of the fruit what do you think is going to happen?
It might sink.
Why do you think it might sink?
Because it'll be losing some of its air
like the tinfoil.
The first time I saw this I was really surprised! You can make an orange sink
just by peeling it.
The reason for that is because
the skin of this orange, and most citrus fruits,
has lots of trapped air inside it.
When you take off the skin you're left just with the denser part of the fruit,
which is why it sinks.
So Vi-vi, we've got some oil here, and oil is less dense...
Lighter? Yes you can also think of it as lighter
than the water in the glass.
It might go on top of the water.
You think it's going to float on the water?
Bubbles!
Is that empty glass?
No it's got water in.
So what's this up at the top? Oil.
Now I've got some red food colouring.
Do you think it's going to float on top of the oil, float on top of the water, or just sink into the water?
Um, maybe one of those three things.
I think it might be one of those three things, yes.
So you just pour it really slowly.
That's enough, thank you.
So what's it done? Mixing up with the water,
it's made a few red bubbles in here.
We've got here these tablets. These make bubbles.
Can you break that one into a little bit? We just need them into quarters.
Do you want to drop one in and see what happens?
Oh now they're rising up through the oil! The red bubbles are travelling through the oil aren't they?
It's pretty isn't it? What's falling back down, by the way?
Air.
No the air is floating to the top.
Oh yeah, the water. That's it.
It's not always obvious which things will float,
and which things will sink, and the science behind it isn't always that
straightforward.
But activities like this are a great way to look at floating and sinking
and introduce the idea density.
They're also a really fun way to encourage children to look closely at the world around them
and to expeRiment.