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The Concise RDWorks Learning Lab with Russ Sadler, Session 2: Basic Science Concepts.
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Now, this first session is all about the physics that underpins the principles of your machine.
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Laser cutting would not exist without an understanding of physics,
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but we do not need the same level of understanding of physics as the guys that discovered all this stuff.
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We just need a very basic understanding of the principles.
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Now, you will not need a physics degree. I’m not going to go into any great detail.
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What I’m going to do is try and paint some little pictures for you, some analogous, pictures that you will hopefully be able to carry in your mind.
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This thing here is called an electromagnetic spectrum. It’s all around you.
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We’ve got radio waves, microwaves. You’ve got your mobile phone sitting in here somewhere.
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You’ve got infrared heaters, you’ve got ultraviolet suntan lamps,
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you’ve got x rays that you go to the doctor and you’ve got gamma rays that come from the sun that will kill you.
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But all of these are waves of energy as we move away from these dangerous rays, which are very,
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very short wavelength and the wavelength is the distance between two waves, the waves become less damaging to us as human beings.
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X rays dangerous. You don’t want too many of them.
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I always remember saying to my dentist, if you’re going out the room while you X-ray my teeth, why can’t I come with you?
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And as we get further up this, it becomes less and less dangerous to us as human beings and our cells.
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But even at the ultraviolet end of this so-called spectrum, if we go out in the sun, we get sunburnt.
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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But unfortunately, that sunburn can also damage our cells.
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This is the thing that you actually feel after sunburn.
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It’s not the heat. It’s the damage that you get caused by ultraviolet light.
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Then we’ve got this range of
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magnetic spectrum here, the our eyes are sensitive to and we can see these parts of the electromagnetic spectrum in the form of the rainbow of colours.
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OK, this is the sensitivity that our eyes have and then we move out of that sensitive zone to something that we can’t see,
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which is infrared energy, which basically is heat, and then we move up the spectrum even further to microwaves and radio waves.
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Well, you know, you can put a transistor radio next to your ear. You can put a mobile phone next to your ear, and it has no effect on you.
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These have only a moderate, very, very small amount of heating effect on your cellular structure.
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They are not sufficiently powerful enough to destroy your cell structures so
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we can go all the way down this part here and not damage our cell structures.
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And then we go into this part here and it gets more and more damaging to us.
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We are going to be using ten point six micron wavelength light with our CO2 laser and that’s sitting just about here somewhere.
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OK, so we’re not too far above the visible spectrum, this wavelength here does not give you any appreciation of what the frequency actually is.
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Ten point six microns here, the frequency is incredibly high. It might be called long wavelength,
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but when you actually sit down and work out what that wavelength means in terms of repetitions, every second the answer is about 28
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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Thousand, Billion. 28 Terahertz.
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Now, that’s a large number of pulses per second of energy.
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If you remember standing in the swimming pool with the wave machine every time a wave passes by it
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has an effect on you. It pushes you, it moves you. Well, that’s exactly what we’re going to experience here.
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We’re going to experience physical movement because of the waves.
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But at 28 terahertz, that’s a lot of pushes, a lot of waves you’re going to experience every second.
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Now, the next thing that you’ve got to understand a little bit about is these things here which are all around us,
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everywhere we look, whatever you touch, whatever you feel, even what your breathing is made up of
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these things. They’re called atoms, and an atom is basically like a little mini universe.
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But at a level that is so small, you cannot even begin to imagine it.
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Basically, we have a lump in the middle called a nucleus, which is the main mass.
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But then round the outside, we’ve got these like planets.
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Every atom has got a different number of planets around it, and they certainly don’t revolve around in a nice uniform fashion like this.
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There’re sometimes several layers and orbits around the central nucleus.
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Some of them are very complex. Some of them are very simple, like this one.
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But they’re all basically this format. Now, if I was to ask you, how solid is that atom?
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Look at it, even if you regard the electrons as being something real, which they’re not.
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It would be, what, ninety nine? Ninety nine point nine percent of nothing?
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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And remember, the whole of our universe is made up of these things. When I look at my cup of coffee here, look, why doesn’t it leak?
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Because it’s got 99 percent of nothing here, it looks solid to us, but in reality, it’s a lot of these things stuck together.
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They’re bound together by almost a magnetic force that holds them together.
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So we’ve got lots of atoms that make up molecules.
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So when you build things with atoms, they become molecular structure and that’s what you see around you.
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There are atoms of pure materials like gold, silver, tin, all those sorts of things, are lots and lots of the same atoms that together.
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But when you look at this PC, this screen, my fingers, they’re not made up of the same atoms.
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We’re made up of lots of different sorts of atoms. And those different sorts of atomic structures that are bound together are called molecules.
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And there are absolutely millions of different types of molecular structures.
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All the materials, the paper, the plastics, water, virtually everything is made up of a combination of atoms.
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And that’s the material world that we live in. But hey, as I keep stressing to you, it’s still ninety nine point nine per cent nothing.
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You see things as being solid, but in reality, they are far from it.
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Different sizes and different types of atom have got different,
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They call bond strengths. So effectively one, one atom might have a very strong bonding ability and another atom might have a very weak bonding ability.
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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So that’s how materials are made up. That’s another important part of your foundation.
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The next concept, again, is all to do with atoms and molecules. So I’ll leave that picture up there and I’ll use my hand to let you know that every
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molecule is doing this. It’s vibrating, there is a concept called Absolute Zero,
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which was discovered in about the 1800’s, where you can lower the temperature to minus 273 degrees C,
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and that’s it. You can get no lower temperature than that. If you go out into the outer reaches of the universe, that’s it.
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That’s called absolute zero minus two hundred and seventy three degrees C.
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And at two hundred and seventy three degrees C all molecular motion stops.
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Nothing is vibrating or shaking at all. So by that definition, as we start raising the temperature above two hundred and seventy three degrees minus.
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Atoms start to vibrate, and when they get to room temperature, they’re doing this, when they’re 273 degrees C hotter.
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So the level of vibration of an atom is its temperature.
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That is a totally fundamental concept that you need to understand,
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for how the laser machine works. Now here we’re looking at the electromagnetic spectrum again, in a slightly different way.
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When you step out into the sunshine, what do you feel? Where’s that heat coming from?
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Well, you’re going to say, yes, it’s coming from the sun because look from the sun, we also get all our light that we can see with our eyes.
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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But in addition to the light that we can see with our eyes, look, the sun is also sending out lots and lots of higher frequency, longer wavelength, light.
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OK, so it’s not at ten point six microns, but it’s certainly here in what they call the infrared region.
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And infrared, you know, means heat. Are we feeling the heat of the sun?
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That’s a very, very big bonfire that you can feel through 90 million miles of space.
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No, we don’t feel the heat of the sun, what we feel is the light of the sun at these infrared frequencies.
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Now, how is it possible to feel light as heat?
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That’s one of the most important concepts that we need to understand now, about how our machine works. When a molecule is vibrating,
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it has a certain temperature. If it vibrate faster, it’s temperature increases.
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Or put it another way, if
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I’ve got a molecule that is vibrating like this, and I can make it vibrate faster by hitting it with waves, pulses of energy.
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Remember what I said to you? Ten point six microns is 28,000 billion cycles a second.
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That’s an unimaginably high frequency.
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But it just so happens that what we’re talking about is the same sort of frequency range that molecules vibrate in.
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So this wavelength is able to do the same sort of thing that you used to do to your mate when you went down the
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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playground with a swing and you pushed him and pushed him and pushed him and he got higher and higher and higher.
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It’s exactly the same principle, you’re using pulses of light energy to push the atoms and molecules and make them vibrate.
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So it’s these pulses of energy, which are actually making the molecules vibrate faster,
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Remember how the atoms are held together, they’re held together with bits of gravity, with bits of magnetism.
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They’re not tied together with any physical thing. And so consequently, ifwe shake them hard enough,
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they will fly apart. As they fly apart, so you’ve got individual atoms that are flying around.
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Now, these individual atoms are still exactly the same chemical.
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They an atom, they do not change their chemistry. The things that change chemistry are molecules.
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So these atoms will go off and they’ll bond with something else and that something else is a different material.
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So let me just try and put that into a little bit of an image for you.
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We’ve got paper. You set fire to paper. Well, are you really setting fire to it?
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What you’re doing? You’re making the molecules get hotter and hotter and hotter.
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You’re adding energy in a different form, but you’re still making those molecules vibrate faster.
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They get hotter, but they’re really vibrating faster and as they vibrate faster, they fly apart.
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And what do you finish up with? No paper, but ash.
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Ash is not paper. It’s a different chemical.
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The molecules have changed, but the atoms have just paired differently with different atoms to make a different material,
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and that’s exactly what happens when we use the laser cutter.
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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We’re adding energy to the molecules and we’re changing them from one chemical structure to another.
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We’ve used the light to change the chemistry of the material, and I hope that’s a concept that you can understand and how it’s actually happened.
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Light turns into vibration.
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And vibration is heat, that’s what you can see, but the molecule doesn’t see heat, it just gets hotter and vibrates faster and faster and flies apart.
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Different frequencies of light can stimulate different molecules in different ways.
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It just so happens that ten point six micron wavelength is a very broad spectrum light that has an effect on most things.
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And we talk about this most things, shortly. You will soon find out that using the laser you do not cut everything at the same speed.
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Different materials react differently to the laser beam.
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And the best way that I can give you a picture of that, is when you were younger, you went to birthday parties.
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They had jelly on the table and they had birthday cake on the table. Now,
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you’re a little bit of a rascal you, and you grab hold of the table and you gently shake the table and you make the jelly wobble quite violently,
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but you’ve only shaken the table a little bit. Have you done anything to the birthday cake? No, the birthday cake is still exactly the same,
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it doesn’t wobble. And that’s basically a good analogy for the difference between materials. The jelly is very loosely bonded together, the structure,
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and it’s able to be stimulated with quite low energy levels.
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Where as the cake is very stiffly bonded together and it requires lots of energy, lots of shaking to make it change.
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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If you shook it hard enough, it would crumble down into nothing on the table, just a pile of crumbs.
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The jelly in the cake analogy is a bit crude, but it shows you what happens to different materials.
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You can shake at the same frequency, but they don’t respond in the same way.
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Some will experience chemical change very quickly and some will experience chemical change very slowly.
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Different materials have got different bond strengths and require different amounts of heat or vibration.
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Those two terms are completely transferable to make it fall apart, explode, self-destruct.
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One final piece of science, chemistry, physics.
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Call it what you want. That we need to just quickly look at is the difference between what I’ve just described,
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which is change of chemistry because the molecules are flying apart and the atoms that fly off bond with other atoms and make new molecules.
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There is another sort of change that can take place as well.
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We all understand water, H2O, and you will understand also that it has three basic states, ice
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which is solid, water which is liquid and steam which is vapor, it isn’t a different chemical.
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They’re all H2O. Steam are micro particles of water suspended in air.
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It’s still water. And if you put a cold surface below steam, it will condense back into water.
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Now, that is something called a change of state, we can do that with a laser beam,
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we can heat water up and we can turn it into steam and then we can collect itagain when we put onto a cold surface.
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So there is another material which works exactly the same as water, but at different temperatures.
Transcript for How Does a Laser Cutter Work: Basic Science Concepts (Cont…)
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And that’s acrylic. Acrylic is solid at room temperature, just like ice. When you heat acrylic up to 160 degrees C,
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I say heat it up, you vibrate it, you stimulate it until its temperature gets to 160 degrees C.
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It’s this vibration level here, and all of a sudden it change to liquid.
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You heat up a bit more,
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and it’s vibration level goes up, i.e. it’s temperature goes up. You excite it with more light and at 200 degrees C, it will turn into acrylic steam vapor.
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You can put a cold surface underneath that vapor and you can collect solid and liquid acrylic again.
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That would become a real bloody pain to you when you start engraving or cutting acrylic, because you will get
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white powder and white substances bonding back onto your surface and you will want to know what that is.
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It’s recondensed acrylic. That’s not a chemical change,
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that is a change of state. You will have to understand how these things play together and it will become more and more obvious as we get through
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further into the subject. How I shall call back on these various concepts and remind you of what’s happening,
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how each one of these scientific concepts is happening at that point in time to cause the effect that we are seeing or want to see.
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Well we’re going to stop at that point,
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because we’ve now hopefully covered the half dozen or so major scientific principles that underpin laser technology.
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If you can understand this first session. You have got a great foundation for building that house.
Transcript for How Does a Laser Cutter Work: Basic Science Concepts
