Hi. It's Mr. Andersen and in this podcast I'm going to talk about candles.
If you're like me you love playing with candles. You love lighting candles. You love relighting
candles. You love playing with the wax. And so most of us know how to play with a candle
but we don't really know what's burning. I mean is it the wick that's burring? Is it
the wax? I can try and light the wax and I can't get that to burn. And so who do candles
burn? Well, first we should start by talking about the different parts of a candle. And
so basically you have the candle part, the wax part. Let me put that smoke out. You've
got the candle part and then you've got the wick part on the inside. The candle is actually
made, usually from something called paraffin. And paraffin is made up of two different atoms.
We've got carbon in the middle of that molecule and then we have hydrogen around the outside.
So in here we might have molecules that are C20H42. That means there'd be 20 carbons,
carbon, carbon, carbon and then hydrogen around the outside. So it's be C20H42. Or it might
be C30H62 or it might be C40H82. And so basically what you have is a hydrocarbon, a bunch of
carbons in the middle and then hydrogen around the outside. But it's not the wax part on
the outside that's burning, what's basically going on is that we are melting this solid
on the outside and it's becoming a liquid. And you can see that liquid pool up on the
inside. But basically what's burning is not the liquid paraffin or the solid paraffin
but it's the gas paraffin. So basically we're heating it up to the point where it actually
becomes a gas. And I think you can see it in this little video that I made. Basically
what I'm doing is I'm first of all lighting a match, and then I'm going to blow out the
candle and I'm able to relight the smoke. And so that's weird. Well, how does that work?
Well let me show you that again in slow motion. I blow out the candle and you can do this
on your own, and if you relight the smoke you can see that flame jump down there. And
so basically what's burning in a candle is going to be this paraffin gas. And it's going
to be right up here on the top. And so you can blow out a candle and then you can relight
that smoke and that's going to relight the candle itself. This will answer that age old
question of how do those party candles work? The ones that are on a cake and you can blow
it out and then it will relight itself. Well the way that works is that you blow it out
like that and then basically what you're relighting is that paraffin that is now a gas or it's
kind of floating up in that area. And the way those trick candles work is they take
a piece of metal and then they wind it around the wick and you can kind of see that crackling.
Basically you blow it out, the metal remains hot and that's actually going to relight that
candle. Another quick thing I wanted to show you is this. If you take a candle and I wanted
to figure out what happens with a candle, if you take a candle and you actually put
it on a balance and light it, well what's going to happen? And so let me show you a
quick video of that. I sped up the video. And so this is the video at about 400% or
4 times the regular speed. And so basically what you can see is the candle's burning up
here at the top but the mass is falling. And so this is reading it in grams so this right
now is at 4.102 grams. And so basically if we were to speed it up 4 times to show you
this, every 4 seconds it's losing 1/100 of a gram. So it's losing quite a bit of mass.
And so a really good question might be, where does that mass go? And when I ask students
this question, like where does the mass go, they have a tendency to say that the mass
is being converted into energy or it's being converted into heat or it's being converted
into light. But if you know anything about science you know that mass can't be converted
to energy and energy can't be converted to mass. I mean it can, but it's rare like that
that's going to happen and then we use e-mc2 to kind of figure that out. But basically
what's happening to that mass, if it's losing the candle, where's it going? Basically it's
becoming two things. It's going to become carbon dioxide and it's going to become water.
And so if we could collect everything that comes from that candle we'd find that the
mass of the candle could be accounted for. There's a law of conservation of mass. In
other words, we're converting that carbon and hydrogen down here into carbon dioxide
and water. What's the other thing that we need in order for that to combust or to burn?
We need oxygen and it's getting that oxygen from the air. And so what's cool about that,
is we could put you on a scale and let you breathe and as you breathe, your mass is going
to decrease as well. So where does that mass go? If we were to put you on a scale, I promise
you, and we were to have you breathe in and out and in and out basically where is your
mass going? It's going into carbon dioxide and water. So it's taking the sugar and the
food inside you and converting that to carbon dioxide and water. It's not like we're burring
it up or we're somehow converting it to energy, or heat, we're actually converting it into
another form of matter. Where was the energy though? Where's the energy coming from? Well
the energy was in the bonds between the carbon and the hydrogen. And as those electron fall
to oxygen in the air, we call this a redox reaction there's a reduction and an oxidation
portion. Basically as those electrons fall to oxygen we release that potential energy
or that chemical potential energy that was in the wax and we release that. In this case
as heat and light but inside our body we release a lot of that as heat but we also release
a lot of that as energy, chemical energy in the form of ATP. That's the energy that I'm
using to move around and do things like that. Last question I would leave you with is why
does a candle look the way it does? In other words why is it pointy at the top? And why
is it not so pointy on the side? Well the reason can be told with the touch test. Essentially
if I were to take my had above the candle and move it down like this I can get my hand
about there before it gets incredibly painful, like that hurts right there. But if I were
to take my finger from the side I could get . . . Ouch! really close on the side until
it hurts. And so basically what's happening is that gas is combusting but it's heated
and so we're getting more of the gas moving up, because as we heat that air it's becoming
less dense and moving up. And so the cool thing I remember reading is if you were to
take a candle and then light it in the space shuttle basically what would happen is that
you would get a spherical kind of ball of flame. Because all of that gas kind of moves
from the center. It's not that there's no gravity in a space shuttle, it's that the
space shuttle continues to fall and so everything is falling with it. And so I think that's
pretty cool. And so why do candles burn? Basically it's the paraffin, it's the wax that's combining
with the oxygen in the air and it's in a gaseous state. And so go play with some candles and
I hope that's helpful.