Stress, Strain and Young's Modulus - A Level Physics | Physics Online | YouTubeToText
YouTube Transcript: Stress, Strain and Young's Modulus - A Level Physics
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so far looking at Springs what we can
see is that you apply a force and the
spring gets longer but this is very much
just specific to this particular spring
I could make a different spring maybe
wind it tight to make the metal thicker
and we'd have very different properties
what it's sometimes more useful to look
at is rather than the actual physical
thing that we've made is the actual
material that it's made from and this is
where we can extend the ideas of force
and extension to stress and strain as
you prepare for exams you might feel at
times that you're under a lot of stress
there's a lot of hard work and then you
feel the strain but in engineering and
physics terms these two words mean very
different things so first of all stress
what's that well basically if you apply
a force to an object then it will deform
so we saw the Springs how you apply a
force the whole thing will move and
basically if you have a force that
causes this causes some kind of
deformation then we said there's a
stress applied and we can talk about the
force per unit
area and the symbol for stress is a bit
of a weird one it's a sigma so stress is
equal to the force per unit area you
have something which is being stressed
then it will change shape and strain
tells us how much something changes
shape compared to its original length
and if we look at strain uh we can basic
uh give the symbol for strain this kind
of Epsilon and that's equal to the
extension over the original
length just be aware that sometimes this
extension is also given symbol Delta L
uh and sometimes the length might be l n
to it might be a capital l it doesn't
really matter about the symbols but this
is effectively how much something got
bigger compared to its original length
now in terms of units well if something
uh is a force divided by area then the
units of stress are going to be given in
Newtons per square
meter and if we look at strain well
strain because it's a meter divided by a
meter it has no units it's a
dimensionless quantity so is stress
related to strain good question it is
the more Force you apply to an object
the longer it's going to get so there is
a relationship between the stress that
you apply to an object and also the
strain that it experiences now this
really does depend on the metal if you
apply the same Force to a piece of
copper as to a piece of aluminium or
steel then they will all change by a
different amount and we can look at this
ratio of stress to strain and this gives
rise to something that we call Young's
modulus now Young's modulus has a symbol
e uh and it's equal to the ratio of the
stress applied to the
strain if we look at mild steel for
example the value of e is about
210 gigap
pascals the reason it's pascals is
because effectively One Pascal which is
the unit of pressure is the same as 1
Newton per square meter which we can
also measure stressing so we can measure
in Newtons per square meter or pascals
and because this is a unitless quantity
for strain that means the units for
stress are also the units for Young's
modulus and it takes a lot of force to
get metal to the to the form so that's
why we have a giga here so about 210
gigap pascals is a kind of uh kind of
value that we all typically get for
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