do you want a sound check mary had a
little lamb the doctor was surprised
i can't get a joke out of him
i'm going to be talking about the symbol
w w is for work and i'm going to
consider changes in work in a rubber
band so i'm going to imagine that i can
make a machine out of a rubber band and
the question is
if i add heat to a rubber band does it
expand or does it contract let me show
you my contraption it's this wonderful
piece of apparatus here as described in
this glorious textbook with a diagram
showing a hairdryer a pivot a rubber
band and a meter ruler only i've done it
the other way and this is very good book
written by somebody not a million miles
away from me who is that is that your
textbook yeah and that's my wife
we wrote it together anyway hang on how
much do you get every time someone's
buys one about 50p
so you're here trying to flog this on
60s yeah it's not not worth it
what i'm gonna do is put this rubber
band under tension and i've got this
industrial heater which will heat up i
can show it well no i'm not gonna show
you that it works but i'll get it on
your arms does it is it hot but i can
confirm that it's hot now i'm going to
put it on the rubber band and as a
result of that this will move do you
expect it to expand or contract i would
expect a rubber band when it was heated
to
expand yes i did okay let's see what
happens as it
heats up the rubber band you can see
contracts and
there it goes way up to the top if i can
get it there
and you can see that the rubber band in
effect has contracted and this
pulling on the rubber band has done work
on my little
figure of robin hood and made him rise
up so i've actually done work on him to
raise him up if i take him off or if i
put it on there it'll come down again ah
maybe like brady you expected whenever
you heat anything it expands because
that's what happens to normal things
like metals if you take a metal rod heat
it up it will move expand and that's
normally what happens but under these
circumstances of having a rubber band a
rubber band is not like a metal a rubber
band is made of long polymer molecules
all stretched out matted together but
they are long molecules so if you pull
this
these long twisted molecules which are
tangled up tend to get straightened out
i can explain it better by getting a bit
of my wife's wool when i started the
experiment the rubber band was taught
other like this it was stretched out and
now if i heat it up
it gets more disordered it wants to
become more jumbled up like that and as
it becomes more jumbled up
it contracts this is when it's stretched
out this is when it's
jumbled up why did the hair dryer make
it want to become more jumbled up well
this is this crazy concept of disorder
related to entropy the hair dryer puts
heat in this raises a disorder of the
system and instead of having it all in a
nice straight line it wants to go into a
more crinkly
screwed up configuration and because of
the syntagment the ends get closer
together and therefore the whole thing
shrinks this is totally
counter-intuitive you would have thought
heat something up it's going to expand
no this is going to contract and it's
going to do work and it's going to pull
the thing up so you can convert heat
directly into work
in this particular experiment and it's
totally counterintuitive i had this
envision you see that you could have a
little man sitting on there and then it
would rise up and i could get him to
come off and then it would go down again
and then i could heat it up again and
another man would come up here and i'd
invent a perpetual means of lifting
people up from one level to another why
didn't you do that in the video because
the man is too heavy if i'd done it in
the video i had to put on a tiny little
cap like that and then it wouldn't
actually break and fall down and i can
now do it with the cap
and the cap will go up to the top
then i can take the cap off
and let it sink down
as i take off this thing and that cools
down
and then i can get another little man
and do the same thing
as impressive which is the cat though is
it i know but the concept is there that
this is a machine
working in a cycle i can heat up this it
contracts it goes up i let it cool down
it goes down again i can do some work on
an object and this is the most
inefficient fanciful fey machine that
you could ever imagine
so that's not how elevators work no no
this is just my strange imagination work