Interview transcript

science student understanding

Research interview carried out by KST with c.17 year old student studying chemistry and physics

This is copyright material - not to be copied or reproduced in any form:

I’m going to ask you some questions about a variety of phenomena, and I would like you to try and explain them for me:

0213 [see transcription conventions]

Could you tell me why you think apples fall to the ground?

Gravity.

0223

Why do you think that apples do not always fall from trees? (What do you think stops them falling?)

Because the tension in the stalk is not surpassed by the acceleration due to gravity, and therefore there is an equilibrium which holds it in balance.

So what’s an equilbrium?

When the point of balance is not exceeded

0249

Why does a suspended spring stretch when a mass is attached to it?

Erm. – Because of the force that’s being applied, a spring is flexible, well it’s not flexible material, it’s a flexible object. And it has, erm, an ability to expand. So because of that ability, that’s why it moves apart.

So as an object a spring is flexible, but the material it’s made from is not flexible?

Well it is flexible to an extent, but not to the extent that if you got just a piece of steel, and attached a weight it would not stretch as much as a spring does. Because it’s coiled, a spring can actually be stretched out further, because the coils can be moved further and further apart and still retain some of their rigidness (sic).

I see, so if you just took a piece of wire made from the same steel, or whatever, (yeah) and you loaded that with a weight,

It wouldn’t, the yield stress of it wouldn’t be as high.

But it would stretch a bit?

Well yes, of course everything would stretch slightly.

So why, why does it stretch?

Because the erm atoms in it are, because of the force being applied, the atoms are being dislocated and moved further apart.

Okay, and by dislocated we mean?

Removed from their original position.

Right okay.

Not dislocated as in dislocation of a joint, but dislocated as in dis- and relocated.

0430

Why does the spring recoil when the mass is removed?

Because the atoms return to their original state and place.

Why do they do that?

To do with how formed to begin with

• • • [see transcription conventions]

I’m not entirely sure, I think it has something, from what I’m aware, it’s mainly to do with erm, how they’re, the form their in to begin with.

Mm?

It’s possible the most comfortable form, it’s the form they are used to being in, it’s the form they are shaped into, and so it’s – it’s a case of returning to it.

So they’ve been formed in that shape, they’re more comfortable. So is that like the ‘natural’ shape for the coil or something?

Well it’s not the natural shape of the materials to begin with, but it’s erm, sculptured, I suppose that’s the wrong phrase to use, it’s made into that shape which then provides it with, erm, a stable environment and then it returns to that stable equilibrium.

0536

Why does the lamp in a torch glow when the torch is switched on?

Because there’s erm a high resistance in the filament wire, and that causes it to heat up and glow.

Why does it do that?

Because of the high resistance electrons can’t pass through, so they get stuck, and that’s when it starts to heat up.

So if it had a low resistance, could the electrons then pass through?

Yes. Well lower resistance. Elec¬ - they do pass through but it’s very, they have to give off s lot of energy to pass through, and that’s what produces the light, whereas if it was at a lower resistance it would not give off as much energy.

0625

Why do you think current passes through a conductor when it is connected to a source of e.m.f. such as a battery?

• • • • • • • • •

I honestly don’t know. My thinking behind it, it’s because they prefer to move from an area of high concentration to low concentration. But in effect, that doesn’t really happen. It’s more a passage of charge.

That’s quite interesting, so what you are saying you’ve got a mental image of what you think should be going on, but you know it doesn’t quite work?

Yes.

That’s interesting, yeah. • • • • • Does that help you think about it, that way of imagining it?

Yeah, I try to see things visually. (Mm) I prefer to see things demonstrated in front of me instead of just copying notes off the board, because if I see how something works, I understand it better.

What about if it’s something you can’t actually see directly, will a model do the job?

Yeah.

0730

Why do you think the planets orbit the sun?

Once again it’s due to gravity, because the sun is a large, well, the sun is a large ball of gas, which has a high density and great mass, and that draws other objects towards it. Although we are not getting sucked towards the sun, we’re in a stable place where we orbit the Sun.

What do you mean by saying stable – stable place?

Well it’s like if you put a ball, a weight on the end of a piece of string, and swing it, it rotates, and the ball doesn’t come any closer, it doesn’t fly off, and the gravity is kind of like the string, it’s holding it in place as it orbits round the sun.

Right so earlier on you were talking about equilibrium, points of balance, is it that sort of idea?

Yes. (emphatically!) There is a balance between, erm, the gravit¬, it doesn’t pull us in, but it doesn’t let us fly off it holds us in place.

So we’re in equilibrium?

Yeah.

0834

Why do you think the moon doesn’t move off into space?

For the exact same reason why we orbit the sun. The gravity provided by the mass of the earth, and the density of the earth, hlds the moon in its orbit.

If somebody was living on the moon, and they thought the earth went round the moon, how would they explain the fact the earth does not fly off into space do you think?

• • • • •

Is that the same, or is that a different situation?

It’s a different situation because the moon orbits the earth, so – as far as they’re concerned if the earth is orbiting the moon, then – earth wouldn’t fly off into space because it was attracted to the moon, and because, perhaps they would consider it to be the centre of the universe, I don’t know. It depends on who it was, their scientific reasoning behind it. Personally, I would think it would be because of erm gravitational attraction.

So if somebody living on the moon were to say that the reason the earth does not fly off into space is because it is going round the moon, and the reason it is doing that is because of the gravitational attraction of the moon towards the earth.

Yes.

Would that be a wrong explanation, or?

In some ways yes, but in other ways no. It would be wrong in the fact that they said it went round, the earth went round the moon, and, but they would not be wrong in saying that there was a gravitational attraction that held it in place, because that is the reason why the moon is in place, it doesn’t just fly off.

Alright, does that mean that the moon’s in place because it’s attracted by the gravitational attraction of the earth, (yes) and the earth’s in place because it’s attracted by the gravitational attraction of the moon?

Yeah. They are attracted towards each other. And if one of them, if the moon wasn’t inside the earth’s orbit then it would alter the orbit of the earth around the sun, and vice versa, if the earth wasn’t there the moon would not orbit the sun.

1036

Have you seen the party trick where a balloon is rubbed on a jumper or sweater, and then stuck to a wall?

Static electricity.

Is that why the balloon stays to the wall?

Yeah.

Could you explain that to me? How that holds it to the wall?

You positively charge the balloon with ions, or negatively charge it, depending on what material you rub it with. And then, because of the high positive or negative charge it will stick to something which is neutral charged, such as the wall, that is earthed, and it will stick against it, ‘cause of the attraction.

So what’s the attraction between?

Positive and negative.

So, if the balloon was say positively charged, for argument’s sake,

It would be attracted to something that was negatively charged, or less positive. Anything that is less positively charged than itself – it would be attracted to.

Okay, so if you had a slightly positively charged wall, and a very positively charged balloon?

They would attract slightly, but then when they got to a certain closeness, they would start to repel. So if you have a neutral wall it will attract the whole time.

Right, so the wall does not have to be negative, it just has to be more positive?

Yeah. But it won’t stick to the wall permanently, because of the, because of the both being positive, it will then move away, then be attracted to it because it’s less positive.

Ah.

It’s electronegativity.

So it’s some sort of moving backwards and forwards is it?

Yeah. Because of, it’s mainly because of electronegativity, which is when something has more or less, erm electronegativty than another item or object, and it’s attracted to it because it’s either more positive or more negative. And it - you can have something that’s very positively charged, but something that’s less positively charged will be attracted towards it. But there is a point where it will, sort of, repel each other.

Okay. If you were trying to measure this amount of positiveness and negativeness, do you know what kind of units you might use for that.

No, actually.

No okay, just wondered. I just wondered if you had a name for this kind of – (well) not that you’re aware of.

Not that I can think of.

1252

What happens to a parachutist when she jumps from a plane?

Erm, starts to accelerate, dueto gravity, so at 9point8 metres a second, and then, after a while free-falling she’ll probably reach terminal velocity, < and then open < [see transcription conventions]

< Ah, < why does she reach terminal velocity?

‘cause she can’t be accelerated anymore because the forces would eventually start to balance out, the acceleration downwards is matched by the upthrust. And the, she would open her parachute, and there would be a greater upthrust so she would de-acclerate, although still falling she would not fall at quite as high speed and the speed would reduce, and then eventually she would land, probably hitting the ground at maybe, ten metres a second?

Is that similar to the situation with the apple hanging on the tree? Where there’s kind of balance, equilibrium? > Or is this different? >

< Yeah. <

Yeah?

The terminal velocity is – there’s an- to begin with it’s accelerating, and then the resistance stops it from accelerating so it just continues at the same speed. It will continually keep on going until, erm a force to slow it down, erm, takes place, to that point they are to an extent, yes it’s in equilibrium, because the velocity is not being changed.

1413

And what do you mean by ‘upthrust’? What’s upthrust exactly?

It’s, upthrust is when, there’s an object falling to the ground, and the air, against is, reduce, produces a frictional force of a kind, and stops it, erm, it’s almost like a barrier to stop it from accelerating any more.

So it would be the same as air resistance, is it another name for air resistance?

Yes, it is air resistance.

Oh, I see yeah.

1437

Have you seen the demonstration where someone holds the dome of a Van der Graaf generator, and their hair stands on end?

Yes

Why do you think their that happens?

The van deer Graff produces static electricity, which is then transferred to the person. And it charges their hair. Because of the hair being charged, erm, the hairs move apart because they are all charged the same. They will have an equal charge, and all be charged positively or negatively. And that’s why they’ll move apart because, erm, two things of equal negative charge will obviously repel each other, or equal positive charge.

Yeah okay.

1516

Have you ever seen magnesium burning in air?

Yes.

Why do you think magnesium burns in air?

‘cause of the oxygen content of the air. Oxygen’s used for, erm, general, erm, combustion.

Okay.

1535

Why do you think chemical reactions occur?

• • •

Numerous reasons, erm, to er, mainly to get a full outer shell of electrons, so, erm they don’t have erm, a single electron in its outer shell or erm one short in its outer shell. So they have a full outer shell because it becomes a more stable element at that point.

So it makes it more stable?

Yes. To an extent. Of course, it will, some you will be able to ?? and some you won’t, some will change their properties. But because they have a full outer sh¬, - atoms prefer to have a full outer shell because there’s less room for erm – it’s – if they’ve got maybe one atom (sic) in their outer shell, they prefer to lose it, because that way they’re – erm they have they get they have a full outer shell, because the outer shell then disappears, and the shell inside it is full, or if they have maybe six or seven erm electrons in their outer shell, then they prefer to gain a couple of electrons in order to have a full outer shell.

Right, okay.

1649

Do you know what the product of the reaction between hydrogen and fluorine is?

Hydrofluoric acid, well hydrogen fluoride, and when dissolved in water it becomes hydrofluoric acid.

Why do you think hydrogen reacts with fluorine to give hydrogen fluoride?

‘Cause hydrogen has one electron in its outer shell, and fluorine has seven. So the fluorine, sort of grabs the electron from the hydrogen, in order to have a full outer shell, and then the hydrogen wants to lose the electron and so it has a full outer shell, because it has no electrons at all then. And so it’s positive chwrged, and fluorine becomes negatively charged.

Okay.…

1735

Do you know what the product of the reaction between sodium and chlorine is?

Sodium chloride, or salt.

Why do you think sodium reacts with chlorine to give sodium chloride?

For the same reason as hydrogen and fluorine, sodium has one electron in its outer shell and fluorine has seven, they both end up with a full outer shell.

1754

Why do you think crystals of sodium chloride don’t fall apart?

Because of the way how erm – the atoms react, you can form a giant lattice, well not a giant lattice, a lattice, because they can, erm because there’s a charge of energy, there’s positives and negatives and so they can balance around each other, and become more stable.

So that makes thm more stable?

Yeah.

‘cause you said when they get a full outer shell, that makes them more stable?

When they - yeah.

Is this different?

Well, yeah because you’ve got the, chlorine will be slightly negatively charged, the sodium will slightly positively charged. So the sodium’s will attract chlorines, and the chlorine’s will attract sodiums and they form a lattice, which has an overall neutral charge.

Okay

1851

Why do you think chlorine molecules don’t fall apart?

Because they share electrons by covalent bonding. So they end up tricking each other into thinking they have a full outer shell.

Ah, that’s interesting, tricking each other?

Not tricking, they sort of agree that they can both share them. And so they, - sounds very much like you’re describing too people. Erm (M:m.) You have – they share the electrons so that each has the satisfaction of having a full outer shell, but they don’t happen to get, they don’t become, erm, negatively charged overall.

Okay.

1930

Why do you think iron crystals don’t fall apart?

Iron or ion?

Iron, like, you know iron as in steel.

The metal.

Yeah.

Erm, I don’t know. Possibly because they are transition metals they can very the number of electrons in each shell and so they can get to a point where they are more stable.

Okay.

1952

Why do you think sulfur (sulphur) crystals don’t fall apart?

Because they can covalently bond, but they also have, erm, it’s the number of electrons in the shells, they can vary the num,ber of electrons in their shells because they have, erm, - they can transfer electrons maybe from their third shell to their fourth shell, and so on, mix around until they get a stable balance. And also they can covalently bond with each other.

Right okay.

2030

Why do you think that ice crystals don’t fall apart?

Ice crystals?

Mm, if you have a lump of ice, why does the lump of ice stay together, what holds it together?

Oh intermolecular forces, van der Waals.

Do you know what they are?

Erm, van der Waals is when you’ve got a sea of electrons which sort of flows around each other. Though, with the case of hydrogen and water it’s more to do with it erm because the water’s hydrogen and oxygen so it’s hydrogen bonding, where the hydrogens polarise towards each other.

What does that mean exactly?

Well you get a dipolar molecule, where erm, the hydrogen is a positively charged, is positively charged, the oxygen is negatively charged, and so you end up with two poles, positive and negative, and they attract other positive and negative poles.

Right, okay.

2127

Why do you think ice melts when it is heated?

Because the molecules gain more energy through the heat, so they have more kinetic energy, and they vibrate more, and then they start to break their bonds between each molecule, and move apart.

2144

Why do you think sodium chloride dissolves in water?

Because water can have, electricity, is a conductor of electricity, erm, and sodium chloride is an ion, you get the sodium ions and the chlorine ions and they move apart, and flow freely through the water, also because water’s polar, a polar molecule, it helps.

Oh, okay.

2215

What do you think holds an atom together? If you had an atom, what holds the atom together?

Well, you’ve, in the nucleus you’ve got, erm, protons and neutrons, and the protons and the neutrons are clumped together, and then you have the electrons round the outside, similar to how a solar system works, with the nucleus attracting the electrons, and holding them in.

Okay

2242

Do you know what the composition of an atom of sodium would be?

I think it’s three electrons, three protons, and I don’t, know whether it’s three or four neutrons.

I think that’s lithium actually.

Is it? Oh sodium, sodium’s the one below, oh it’s, in that case it will be eleven electrons, eleven protons and either eleven or twelve neutrons.

Yeah, I think it’s normally twelve. Erm, do you know how the electrons are arranged?

Erm, two in the inner shell, eight in the second shell, one in the outer.

2316

Do you think that the atom could fall apart? Do you think that the outer electron could fall out?

The outer electron can escape, due to shielding by the inner two, erm, electron shells, which - as the name says - it provides a shield from the attraction of the nucleus, so if there’s something that’s erm, perhaps got a more positive charge, or is able to erm extract it then it works/wants a greater pull provided by the nucleus of another atom then it will be transferred.

It won’t just fall out then?

Erm, well you can knock electrons out, but the process of doing it requires a very high amount of energy.

So a scientist could remove an electron from a sodium atom?

Yeah.

2409

And what would you have left if you took an electron out of a sodium atom?

A sodium ion.

Do you think it is possible to remove a second electron, i.e one from the ion?

Yep, second ionisation energy.

What would you have left if you took a second electron out?

Technically, with the number of electrons it would be fluorine, but it would actually be a sodium two-plus ion. It would have the same number of electrons as fluorine, but because of the number of protons and neutrons it would still behave similar to the properties of sodium.

2438

Do you think it is easier or equally difficult or harder to remove the second electron?

It’s harder because there’s a greater pull from the positively charged nucleus. The nucleus will have the same charge but it will transfer more energy to each atom, er each electron, with every electron that’s removed. (Ah.) Because the, if you’ve got, erm eleven, if you’ve got elven cakes and eleven people, each person gets one cake, if you’ve got eleven cakes and ten people, each one gets one, and one tenth. When you get nine every one gets one and two ninths and so on.

So it’s a kind of sharing out process?

Yes.

What is it that’s shared out?

The charge.

Right so the nucleus has got a certain amount of charge, > that’s shared out amongst the electrons available? >

< Positive charge, yes. <

2528

Is it possible to remove a third electron?

Yep, third ionisation energy, although it requires more energy than to remove the first or the second.

Was that for the same reason?

Yep. Because the pull from the nucleus becomes greater so you require more energy to remove it.

And the reason the pull becomes greater – is because? • • Same reason as before?

More energy is being shared between fewer, the same amount of energy is being shared between fewer electrons. Yeah, so each one receives more.

2527

Do you think that the nucleus of the sodium atom could fall could apart?

Yes.

So what do you think holds it together?

I’m nor entirely sure.

But it does hold together, does it normally?

It holds together, but it is possible to split it because it’s made from protons and neutrons.

2617

Why do you think some atomic nuclei are unstable?

Erm – I’ve been told why they are, but I don’t understand why they are. We’ve been told they are because erm the way, their composition, doesn’t make for it to be a stable element under normal earth, under normal atmospheric conditions on earth.

(Can’t argue with that.) So you’re not happy with that explanation?

Well, no ‘cause I, that’s what I’ve been told but I don’t understand how it works, erm I know it means they’ll fall apart but it doesn’t really explain why very clearly.

Yeah. So it seems to be question ‘why are they unstable’, answer ‘because they are not stable’.

Yeah.

Yeah, okay.

2706

So the fact that some hold together and some of them don’t's a little bit of a mystery?

Well I know some of them I know a lot of them hold together because they’re, they’re in a more stable state and form, but then erm radioactive atomic ones – when there’s more than a certain amount of it in one area, like plutonium I think it’s when there’s more than eight and a half kilogrammes, that’s the point where it then produces severe radiation and radio, erm er EMP and everything’s given off

Right so a critical mass we are talking about are we?

Yeah.

Yeah, I see, I see. …

DEBRIEFING:

Thank you very much for your time today, and your patience in answering my questions.

how did you feel during the interview?

It’s okay, some questions were quite awkward.

Did they make you feel uncomfortable, or was that okay?

No they just made me realise that I perhaps don’t quite know as much as I thought I knew about the subjects I’m doing.

…

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