WELCOME TO
PROTONS FOR BREAKFAST
SPRING 2011
WEEK 4: GLOBAL WARMING
1
PfB13 Week 4
These are the feedback questions & comments from Week 3 (16 MARCH 2011).
You said…
I said…
Really enjoyed the session – I feel like I’m learning something new Excellent!
each week – Great ice cream too!
• Mmmm. Air is a mixture of mainly nitrogen (79%), Oxygen
• If air is a mixture
(19%) Argon (1%) together with trace amounts of H20 and
of gases what
impact do they have
CO2. These molecules are constantly bombarding all the
on the things they
surfaces of everything all the time – each atom on the
touch e.g. the
surface of a solid is being hit around a million million
furniture
times every second!
surrounded by air or • If the average speed of gas molecules is faster than the
even us?
average speed of molecules in the solid, then on average
the gas molecules slow down, and transfer some of their
• Do the
energy of motion (called ‘heat’) to the cold object.
temperatures
change?
• You are welcome!
• Thanks for answering my question last week.
• Glad you liked the ice
• Interesting presentation and good ice cream!
cream
• At first I wasn’t very enthusiastic about coming, but
• I am glad you are
now I think it’s quite interesting and ‘boggling’.
beginning to enjoy it.
Everything is better explained than at school!!!
• Yes. They emit gases such as CO2 and
• Do volcanoes contribute to climate
change?
clouds of fine particles, both of which
affect the climate.
• Is there anything we can do about it if
• No.
they do?
• Delicious ice cream. Thank you ice
• You are welcome. And yes, are they not
cream makers!
a great team!
• I know! I am amazed each time
• Infra-red handprint on the wall was
too!
amazing!
• You are welcome
• And thank you for the delicious ice-cream!
• You are welcome. Well you can
• Thanks for a fun and enlightening session!
write any questions you think
Hmm…. no questions I can think of right now
down when you think of them
but I’m sure I’ll think of something as soon as I
and bring them along next
get home.
week.
• The ice cream was delectable and tickled the
• Indeed.
atoms on my tastebuds!
• ? A paradox
• Heat is cool!
2
You said…
I said…
• I love the songs. • Me too
• It is wonderful stuff.
• The nitrogen,
when you poured • Well observed. It was because cooling the rubber of the
balloon changed its properties. Rubber is made from many
it in the bucket,
long molecules of latex which are all mixed up higgledywas really cool,
piggledy (and ‘Yes’, that is a technical term☺).
steam/mist went
everywhere,
o At room temperature the molecules jiggle a lot and as the
when I put my
rubber is stretched the molecules can work their way past
hand in the mist
each other. So an object made of rubber can change its
it felt really
shape dramatically.
cold.
o When cooled, the molecules jiggle much less and the
complex network of molecules becomes locked together.
• Why does the
So when an object made of rubber is cooled it becomes
balloon make a
much more rigid.
cracking sound
when you take it • The sound you heard was the sound of various bits of the
out of the
rubber (which were still cold and rigid) ‘creaking’ as they
nitrogen?
became stretched as the balloon expanded
• Good point. It has taken people several hundred years
• How do you work all
to figure this out and it may look like I am clever, but I
this stuff out?
am not. I am just familiar with this way of looking at
• How does dry ice
things.
work?
• I am not sure what you are asking here. In the same way
that liquid water is just condensed water vapour, and ice
is just solid water, so dry ice is just cooled carbon
dioxide. It has been cooled so much that the molecules
are moving so slowly that when they come near each
other they stick together.
• Thank you.
• This week was more
awesome than the
• Yes, halogen bulbs are typically ~300 °C hotter than
other awesome weeks.
conventional incandescent bulbs. And yes, the current
does affect the temperature of the bulb. Running a bulb
• Are halogen bulbs
this hot causes the tungsten to evaporate (yes!
hotter than other
evaporate!) so fast that a normal bulb would darken as
ones and does the
the tungsten was deposited on the inner surface of the
current affect it?
(relatively cold) glass. In a halogen bulb, a small amount
of iodine (usually) is put inside the bulb and this reacts
with the deposited tungsten to make tungsten iodide. If
the glass is made extra hot – around 250 °C – then the
tungsten iodide evaporates from the glass and redeposits the tungsten back on the filament! What a
great trick!
• Thanks again! It was really interesting and I’ve learnt so much • You are
yet again!
welcome
• Oh yeah, and thank you for the ice cream – it was delicious!
Very informative and fun as always!
Everyone is being too nice this week! But
Thank you and cannot wait for next week!
thank you any way ☺
3
You said…
•
• Where can I get
liquid nitrogen and
dry ice?
•
• I knew this is
irrelevant…. but
where do you get
•
your cookies from?
Their lush!
• Loved the ice cream.
• How much did the
Hovercrafts cost?
• Do they use liq.
nitrogen in commercial
ice cream making?
•
•
•
Why can’t we see
the infra red light
and the camera can?
How did you find out
that atoms send out
waves?
Today was amazing!
I loved all the
experiments and the
hovercrafts! It was
great.
I said…
If you are teacher and would like to be trained to use liquid
nitrogen, please contact us and we can help. Our liquid
nitrogen is supplied by BOC
Dry Ice comes from Yara and is available from their
Heathrow plant via mail order.
Mmm. They are supplied by a our catering team. I will
investigate to find out whether ‘lush’ is a compliment, and if
it is, I will pass it on. Thanks. I think.
• ☺
• £450 each, but see my blog for a cheaper version
(blog.protonsforbreakfast.org)
• Liquid nitrogen is used in many ‘cook chill’ processes
where cooked food must be chilled rapidly to make
packaged meals – fresh or frozen. However ice cream
needs to be stirred as it cools so I am not sure if liquid
nitrogen is used in that application. There is also a
business in Camden which sells ice cream made with
liquid nitrogen: http://www.chinchinlabs.com/
• The infra red light that the camera detects is being
emitted all around us all the time. Including from inside
our eyes. So there is just too much of it for us to ‘see’
with it. It would be like to trying to take a photograph
using a camera that had a light inside the camera
constantly overloading the detector.
In order to work, the thermal camera uses a miniature
refrigerator which cools its detector and its local
environment to -200 °C (Yes: inside the camera!). At this
temperature very little infra red light is emitted by the
components of the detector so when the infra red light
falls on the camera, from outside focussed by the lens,
the detector can ‘see’ the image.
• People have known for sometime. Firstly people noticed
that hot objects - even when they were not visibly glowing
– still seemed to emit radiation of some kind that warmed
detectors (usually small thermometers). You are familiar
with this because you feel the warmth from a radiator
from a distance even when it is not glowing with visible
light. Then people looked at the spectrum of visible light
from glowing hot objects. They noticed that when they
used detectors other than their eyes to look at the
spectrum, (e.g. cameras or other light sensitive
instruments) that they could detect radiation beyond
where the visible red part of the spectrum ended.
• Glad you enjoyed it.
4
You said…
• Why can’t you go any
lower than –
273.15 °C.
• Why is there an
absolute zero?
• Why isn’t there a
similar thing for how
hot heat can get?
•
•
•
•
•
•
•
I said…
• Because temperature is a measure of the speed of
molecular motion, and molecular motion ceases completely
at absolute zero. This defines absolute zero (0 degrees
kelvin) exactly.
• On the absolute temperature scale, water freezes at
+273.15 degrees kelvin. On the celsius scale, water
freezes at +0 degrees Celsius. Since the size of a degree
celsius is defined as being equal to a degree kelvin, water
freezes at −273.15 degrees celsius exactly.
• Absolute zero is the lowest possible temperature because
molecules can’t go slower than not moving at all. There
isn’t a highest possible temperature because there is no
limit to the amount of energy microscopic particles may
possess,
• Well I feel obliged to mention that stars
When a star dies does it
aren’t alive in the first place. But when the
collapse in on itself?
nuclear fuel within a star is used up, then
Have you listened to the
gravity will cause the star to collapse.
Electromagnetic Spectrum song
on You Tube?
• I have now, and I have to say I prefer the song
I played you.
The bit on the back is not blank
• Ahhh. We used to have text which read
it has words on it.
‘Except for this writing, this page is
intentionally blank’, but it seemed a bit
pedantic.
• Absolutely so. These concepts are not
Although I was useless at physics at
at all obvious and are very hard to
school I have found the basic concepts
grasp. It takes a long time for them to
fascinating and it’s taken a long time to
feel ‘familiar’ and so allow one to think
understand them!
about them.
Michael’s lectures are full of infectious
• Thank you
enthusiasm!
• They are great opening up our eyes to
I took the glasses back to school and
another dimension of light.
the children had fun looking through
them and discussing colours in
• Not quite. Temperature is a measure of
connection with a ‘colours’ poem and
the average speed with which atoms
bizarrely Red nose day!
and molecules move, but on average
they don’t travel in any particular
If temp is a measurement of the speed
direction – the directions of the
with which atoms and molecules move is
molecules are random. Also the atoms
it actually measuring the electricity
and molecules are electrically neutral
generated by the movement of said
so they don’t carry and electric
atoms?
current. I am not sure this exactly
answers what you asked.
5
You said…
• If all atoms ‘jiggle’ –
does everything
send out waves
measured in ‘hertz’ –
e.g. does a solid send
out a wave
measurable in
hertz?
• Do we see colours in
solid objects
because of the
amount the atoms in
that solid are
jiggling. …..or am I
confused??
•
•
•
•
•
•
I said…
• Mmmm, Yes. All substances – solids, liquids and gases emit infra red light. At room temperature, solids emit
electromagnetic waves with a range of frequencies
including microwaves and infra red light. The exact
spread depends on temperature. At around room
temperature the peak frequency is approximately 60 THz
i.e. 60,000 Ghz or 60,000,000,000,000 Hz. The waves at
this frequency have a wavelength of approximately 0.005
mm.
• You are a bit confused. Assuming the solid object is not
hot enough to be a source of visible light (as opposed to
infra red light – see your first question) then we see
colours in objects because of the way they absorb and
emit the light which falls upon them. Light is an
electromagnetic wave and certain frequencies are
absorbed especially strongly by particular molecules – we
call them dyes and pigments.
• We buy from BOC, who can deliver to you if you are set up to
Where do
receive. If you are school contact Andrew Hanson and find out
you buy liquid
how to get some for free, along with training.
nitrogen?
• I don’t think a black hole leads anywhere. There are – to the best
Where does
of my knowledge – no unambiguously identified black holes – only
a black hole
very heavy dark objects which cannot be seen directly. So ‘black
lead?
holes’ is what we think will happen to matter at extremely high
What is a
density, but we really don’t know how they behave. What we have
gamma ray?
instead are thousands of theorists who can speculate how they
Love it! Still
a bit boggling
might behave.
but love it!
• A gamma ray is very very high frequency electromagnetic wave.
o Visible light is emitted when an electron in the outer orbits
around an atom (a valence electron) is disturbed.
o Ultra violet light and X-rays are emitted when an electron in the
inner part of an atom is disturbed. Because they are nearer the
nucleus, the electric field is much more intense than it is for
valence electrons, and the forces on electrons are consequently
much greater.
o The electric force is not usually strong enough to accelerate
electrons faster than this. Gamma rays are created when
protons within the nucleus are disturbed. The vibration of the
proton is caused by the strong force, but because the protons
are charged, a high frequency electromagnetic wave is emitted.
• Indeed.
The hovercraft gave a whole new
• I am glad – maybe it was worth it after
dimension to the learning of science.
all.
Ice cream was very good – Thank you.
• You are welcome
6
You said…
I said…
• Do you mean in a light bulb? Yes, that would be a
• Because the light is so hot
risk, and that probably controls just how small
shouldn’t it shatter the
light bulbs of a particular power can be made.
glass?
• A protein called keratin – like finger nails but
• Nothing to do with tonight’s
discussion but what is hair
long and thin.
made of.
http://en.wikipedia.org/wiki/Keratin
• The most interesting and
• Thank you. I can’t really talk about volcanoes,
exciting discussion yet, today
but I can tell you that the reason the interior of
I learnt about volcanoes and
the Earth is so hot is because of the radioactive
how they are formed (in
decay of Uranium, Thorium and Potassium which
school) can you give me a
are present as traces throughout nearly all the
more detailed explanation.
rocks on Earth.
• Is bread dough a solid • Great Question. The categorisation of substances into
solid, liquid and gas is really useful, but does not cover
or a liquid? This
all the structures in which we find matter. Bread is
always confuses me, as
really a foam – a class of materials all on their own with
it looks like a solid,
but it can move easily
properties that vary critically with the size and density
and stretch.
of the bubbles. Most importantly, many biological
substances are really intermediate between liquids and
• Thank you again, I had
solids. They occupy a category known as liquid crystals,
a brilliant time and I
can’t wait until next
which also have many technological uses in displays.
week.
• You are welcome.
• Thank you for doing your homework. Wow −71 °C! Very
• Yakutia coldest
chilly.
populated place
(Siberia).
• Ha Ha!
• Not sure I understood • Mmmm. This is a very much abbreviated story. But here
goes…The electrons which orbit atoms behave like tiny
the ice cream
electromagnets. But if two electrons orbit the same
demonstration – could
atom they tend to orbit the atom in opposite senses –
you do it again next
one clockwise and the other anti-clockwise - so their
week please!
magnetic fields cancel each other out. However in some
• How are the atoms
atoms, such as terbium atoms, a whole group of
generating magnetism
electrons (6 in the case of terbium) all orbit in the
– is it electricity
nucleus in the same sense. At high temperatures, the
again?
electrons orbiting one atom are not aligned with those
orbiting a neighbouring atom – and so the magnetic
properties of a large group of atoms are not too strong.
When we cool the atoms they stop jiggling so much and
line up and create an awesome magnet!
Mmm. Good point. I hadn’t thought of that.
So presumably any induction hob can only
heat to a certain temperature (if it has no But that only limits the temperature to
~780 °C at which point the pan would red
restrictions) because after that the pans
hot!
would no longer be magnetic?
7
You said…
I said…
Typically 1000 °C. When you can just see the dull red glow
What would the temp be
of something the temperature is around 700 °C. Steel
of a roaring fire in the
begins to melt at around 1300 °C and I doubt you would be
house made of wood,
able to achieve that in a fire without additionally blowing in
wallpaper?
air with a bellows.
Loved the ice cream and
sorbet – Thanks!
You are welcome
I am glad that you are now
Thank you very much for, yet again, another brilliant
presentation. I have really learnt a lot today and atoms friends with atoms. I hope you
will stay friends for life.
are now my best friends!
Yes, the liquid nitrogen makes a shocking sound when it
Enjoyed the sound of the
falls on carpets. When it falls onto a smooth surface it
liquid nitrogen as it was
lasts for many seconds before evaporating. When it hits
sound. A bit similar to the
the carpet, it instantly turns to gas – hence the sound as
water “boiling off” in the
the ‘shock’ wave travels away from the carpet.
frying pan.
Another cool
I am not quite sure how to take that but I think it’s a compliment,
evening with our
Thank you.
hot presenter!
A. Its not just NPL: no scientists use °F anywhere in the world.
Only the inertia of the public in the USA keeps the unit alive. The
Q: When did NPL
stop using °F? And main internationally agreed unit of temperature is the kelvin (K).
This is zero at absolute zero and 273.15 K at the ice point and is
why?
linked directly to the speed of molecules. The celsius scale is just
offset from the kelvin scale so that it starts at −273.15 °C
(absolute zero) and has the value 0 °C at the ice point. Thus the
degree Celsius is linked directly to fundamental definition of
temperature. The degree Fahrenheit has no fundamental link to
temperature and is defined with two arbitrary fixed point
temperatures. So although it is familiar to older attendees here
(including myself) it is not linked to basic physics.
• Thank you
• Good session.
(Tasty ice
• Well no one has measured it – the centre of the Earth is 6400
cream).
km deep and the deepest hole we have drilled is just a little
over 10 km deep! But by modelling, and examining the passage
• What is the
of seismic (sound) waves that travel through the Earth, we
temperature at
deduce it is approximately 5500 °C, just below the
the centre of
temperature of the surface of the Sun: ~6400 °C
the Earth?
8
You said…
• Very interesting – I
learnt and revised lots
of things as you showed
us this lesson when you
visited our school
(Waldegrave).
• I learnt about iron and
how it loses it magnetic
field when heated.
• Why is the Earth’s core
not magnetic? – if iron
loses its magnetic field
when heated?
Years ago, the fridge we
had was a Kelvinator!
I said…
• Thank you: I feel happy whenever anyone remembers
anything I say!
• Excellent, well remembered
• The Earth’s core is not magnetic for two reasons.
Firstly it is too hot – way too hot! And secondly, the
pressure forces iron to adopt a different crystal
structure which is not magnetic. The Earth’s magnetic
fields arise from electrical currents which flow in the
liquid molten metal part of the Earth’s outer core. It
is an unsolved problem – no one knows exactly how the
Earth’s Geo-Dynamo (what we call the system that
generates the Earth’s magnetic field) works. Perhaps
you could solve the problem for us ☺?
Yes! – what a great name! Instead of having a fridge
called that I had to call my son Kelvin! Still I guess it is
better than having the fridge of my dreams and a son
called Bosch!
Does everything become
Not everything, but many things. When the chaotic
magnetic when it’s cold
jiggling of atoms dies down many solids adopt ‘ordered
enough?
states’ which are magnetic or superconducting.
• Yes It’s Motion Motion Everywhere!
• Wowza! So much going on around me
that I didn’t realise.
• I don’t know why the connections are
not made clearer. I suspect it is
• I’m so impressed with how you can
associated with the ‘unit structure’
explain and demonstrate these
concept inherent in many syllabuses,
concepts so clearly. Why aren’t all
and the fact that many GCSE’s and A
these connections made clear at second
levels can be passed without ever
level/school?
taking an exam on the whole syllabus.
• Well, thank you for the lecture. I’m
delighted with what I’ve learned
• Glad to have a happy customer ☺
tonight and I’m really looking forward
• Yes, many people are familiar with a
to next week.
great deal of science – but the
connections between the areas of
• The connections between things really
science are often not appreciated.
are so important (for my
understanding).
• I have really enjoyed this session and I • Thank you.
loved every minute.
• I hope so too. Do get back in touch if
you think we can help: we can give
• Thank you so much for making these
teachers training in the use of liquid
concepts and ideas much clearer in my
nitrogen and loan equipment and
own head through the use of
nitrogen. And maybe you can send your
demonstrations and interactive
students and their parents?
resources – I hope this will improve my
own teaching practices.
9
You said…
• Is there a lot of competition for places
to work here?! It’d be a while but I’m
interested in this stuff and it would be
good to know.
•
•
Why does an
energy saving
bulb take a
period of time
to reach
optimum
brightness? In
comparison to
Std bulbs?
At absolute
zero are all
atoms
perfectly still?
•
•
I said…
• Yes, but if you complete the course you
will receive a sought-after Protons for
Breakfast certificate. If I were
offering jobs, that would be the only
qualification that I would ask for.
It needs to heat up! Inside the tube a ‘spark’ is passed though
mercury vapour. As the electrons ‘bash’ into mercury atoms the
mercury atoms ‘ring’ like a bell and give out a characteristic
spectrum – you saw the strong lines in the spectrum using the
glasses. Also the atoms emit ultra violet light, which causes a
coating on the inside of the tube to fluoresce and give off
visible light. The brightness of the light given off depends on
the density of the mercury vapour – the more atoms of
mercury the brighter the light.
Mercury is a liquid at room temperature, but evaporates to
sustain a vapour above its surface. The vapour pressure varies
very strongly with temperature. When a bulb is cold, the
density of the vapour is low and the bulb is not very bright. As
its temperature rises in use, more mercury evaporates and the
vapour density increases, making more collisions and giving off
more light.
Prompted by your question I put a compact fluorescent bulb in
the freezer (~-18 °C) over night, and then I plugged it in and
measured its brightness with a light meter. As it warmed up it
became 25 times brighter! Try it! But be careful not to get
condensation on the bulb. Light meters are available from
Maplin’s in Kingston.
Yes.
10
You said…
• What would happen if
the atoms stop
jiggling altogether i.e.
reach 0 °K? Collapse?
Black hole?
• Is it possible?
• How does light travel
to us from the Sun? I
know that a light wave
is a disturbance in a
field but what is the
field made of? Is a
field “made” of
anything? I find it
difficult to
understand that you
can have a field in a
vacuum (it is a vacuum
between use and the
sun, isn’t it?)
• If cosmic rays are
‘particles’ how come
they are still part of
the electromagnetic
spectrum of
‘radiation’? Is it
because radiation and
particles are not
entirely separate?
I said…
• Nothing. Absolutely nothing would happen, because
nothing would move!
• Sadly, No, it is not possible to cool something to
absolute zero. In order to cool something, you need to
put it in contact with something cooler. Then the ‘fast
moving molecules’ slow down when they hit the ‘slow
moving molecules’. If absolute zero is the coldest
temperature possible, then it is not possible to have
anything colder than absolute zero, in order to cool an
object down to absolute zero. If you see what I mean.
• Great question which indicates to me that you have ‘got
it’. The field is not made out of atoms, and yes, it is
present in a vacuum. The reason you find this difficult
to understand is because it is difficult to understand.
The space between the Earth and the sun is mostly
empty of matter, but there is a constant stream of
particles, protons and electrons, streaming away from
the Sun. Even in intergalactic space, away from all stars
there is around one hydrogen atom in every cubic
centimetre of space.
• Sorry: poor communication on my part. When the song
was recorded, the nature of cosmic rays was not known.
What we observe on Earth is ‘shower’ of secondary
particles and a brief flash of light created when a high
energy proton hits the Earth’s atmosphere. We never
observe the original particle which caused the shower.
It took a long time before people realised that this
‘cosmic’ radiation which pours in at us from all directions
in space was not caused by super high energy gamma
rays, but by particles – high energy protons.
I’m sorry I can’t follow this question. In
When you “froze” the balloon you’d blown
one balloon was carbon dioxide that we had
into what was left in the balloon – liquid?
put in earlier as a solid. In the second
Just to say I thought this week was
balloon, I had blown in air. Air from my
brilliant – even better than the previous
lungs has more water and carbon dioxide
two! Thank you.
than normal atmospheric air.
Glad you enjoyed it .
11
You said…
• So glad you told me
about atoms, proton
and neutrons
because I am just
being taught about
it. It has made it so
much easier!
• Why is it that the
balloon deflated
when you put it in
the liquid nitrogen
but the cup that you
put in to pick up the
liquid nitrogen didn’t
do anything?
I said…
• It’s funny, often the first time you hear something it is
strange and difficult, but the second time it is much
easier. I think its important to become ‘familiar’ with
ideas first before one tries to formally ‘learn them.
Anyway, I am happy it helped.
• Mmmm. Interesting question. Well, the balloon deflated
because it was filled with gas – and when we cooled it, we
slowed down the gas molecules and they could no longer
push out the walls of the balloon, and the pressure of the
air caused it to collapse. The key point is that the
structure and size of the balloon depended on the gas
pressure.
• I guess that you noticed I was using a foam cup – full of
bubbles. The plastic is called poly-styrene but I don’t
know which gas is inside the bubbles. I think you are
asking ‘Why didn’t they collapse?’ Well the gas inside
them, would certainly have had its pressure lowered, but
the foam structure around the bubbles is strong enough
to form a rigid structure and doesn’t rely on the pressure
within the bubbles to determine the shape of the cup.
• From the air. First one compresses air to around 200 times
• How do you
its normal density – it becomes enormously hot and one
harvest liquid
extracts this heat and cools down the gas back to room
gases?
temperature. Then one expands the gas, and it cools as it
• When you freeze
expands and turns to a liquid – liquid air, a mixture of liquid
food is it
oxygen, nitrogen and argon. I think the gases are then
preserved
separated by distillation – they boil at different
because the
temperatures.
molecules have
slowed down?
• Basically yes. The bugs in and around food – algae and
bacteria – can only function well in a certain temperature
range. Cooling them down slows down the rate at which they
can reproduce though in general it does not actually kill them.
• You weren’t there in the first half? Aaargh! Well
As I wasn’t there in the first
its difficult to summarise, but basically,:
half, what was the experiment
with the white smoke, which is
o everything is made of atoms
actual cold? Anything I should
o atoms are constantly moving
really know for the next
o temperature is a measure of the speed of
session?
motion of the atoms
Can’t there be a moment where • Not quite. I have oversimplified the dynamics of
electrons with an atom. Actually it has taken a long
the electrons are all in the
time to figure out exactly how they orbit, but it
same distance to each other
turns out that they orbit in ‘shells’ at particular
and the proton?
distances from the nucleus,
12
You said…
I said…
I told you this week would make more
I understood a lot more today and was
sense – and also help make sense of the
very interesting. The chocolate ice cream
other weeks.
was especially yummy!
• When atoms reach absolute zero do they stop moving.
• Yes.
• Why do you wear pink shirts all the time.
• Do I?
• It was great. I loved it.
• Excellent.
I understood most of it! Good talk.
Great!
• Yes, they are fantastic substances
• Amazed by the carbon dioxide and
that really make one think about
liquid nitrogen.
extremes of temperature, and its
• Thank you for a great session.
effect upon matter.
• You are welcome
• Excellent
• I really enjoyed this week.
• They cost £450 and work really well on
• How much are the hover crafts
smooth marble or granite floors – but sadly
because I would like one, to get
do not work on rough surfaces or – in this
to school! Up the River Thames.
case – on water!
• I love the idea of freezing
balloons.
• It is my favourite demonstration of all time.
I’m getting there! Beginning to understand Excellent – takes a long time and the
how everything is linked together – thanks! connections keep coming!
We can’t because we live in a world full of light and go to sleep
Why can’t we
sense sound in the when it is ‘dark’ i.e. no light. Animals which live in the dark, such as
bats or dolphins, can most certainly ‘see’ with sound. And we can
way as light?
create devices (called SONAR) which ‘see’ in the dark using sound.
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