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going to talk
about fiction
something
i'm terrible cold
my voice is down
to get through this was my beliefs thank you
to talk about fiction which we have never dealt with
friction is a tricky thing
not as easy as you might think
i don't object
on horizontal surface
of that has a mass and
gravitational force and g
white-out action
was completely ecstatic shin
there must be a force pushing upwards
surface
to cancel out and jim because there's no acceleration
into whatever time
we normally call that the normal force because it's normal to do surface
and it must be misunderstand g
otherwise it would be an acceleration in the white addiction
hi i'm going to push
on this object
which of course
forcible tooling
and we know
but the object in the beginning of all not start accelerated
why is that
that's only possible
because there's a frictional force
which but just itself
exactly compromised force
i push harder
and harbor and harder
comes a time
that irene
and object begins
accelerate
it means that the frictional forces
which is growing all the time as i push harder
reaches a maximum value which it cannot exceed
and that maximum value
constriction
and achieve
this is an extreme mental fact
is what's called the friction coefficient new
which has no dimension
times
normal cells
we make a distinction between
static
friction coefficient
and connecticut
disease
to break it looms
to get it going
this is
to keep it going when it's already has a certain velocity
static is always larger
connecticut for reasons
there are quite obviously too bill hartley
kab richard lewis ones it's going
it's easier to keep it going
it is fairly easy to measure
friction coefficients
by putting an object
incline
and light
changing the angle of the incline
increasing it
india and all but
your increases to this point
that the object
startups like
purity object
gravitational force and g
which i will decompose
two forces
into why the election which aren't always choose
perpendicular total surface
and another one
in the next election
you're free to choose this plus
with this plus
i will not use
this plus correction
i'm going to decompose them
so i have one
component here
this component equals and g
aren't the coastline
qualifier
and i have a component in the eccentric shin
which is
and g
signed off
there's no acceleration into wider action
so i can be sure that the surface
pushes back
within normal force and
and that normal force and
must be exactly
energy co-sign also because those are the only two forces in the white every
action there's no acceleration in the white election
so this plum must be
and jean
cosine
now these object wants to slightly downhill
friction prevented from doing so
so it is going to be a frictional force
in this direction
and as i increase the killings
this fictional force
we'll get larger and larger larger and then the comes a time
if you object will start to slight
let us evaluate
that very moment that it's just about to break loose
i'm applying newton's second law
in this direction now the acceleration is still zero
but the frictional force has no just
reach the maximum value
because i think result file
so this component will get larger and this component will get larger
this component will get larger this component is still holding
its own but then all of a sudden it can't go any further and start to
accelerate
so new tunes second lol tells me
that angie
final thought
minus
at maximum
at this point zero
and this one
these new static
tiles ben
witches and jean
coastline or hot
this one's andy
klein off our
is equal to europe
i lose my energy
and to see that you will pass
equals
dependent off-track that easy
to measure
so you increase the killed we will do that later
until it starts to slip
that critical angle that it starts to slip
you have a value from your grasp of static friction coefficient
it is very low intuitive
that this friction coefficient
is completely independent of the mass damascus disappeared
think about that it's very known intuitive
if you double the mass
the angle would be the same given the fact that you have the same kind of
object to purchase coefficient
all the defense
although the materials that you have the materials that are robbing over each
other
it's also independent
over the surface and weird isn't contact with these
inclined to teach decoding on into which it
it's willing to with you
but we will see
that that's
quite anxious wasn't do certain things that we can measure it
if you have read a car you park your car
you throw it on the brakes and you put that in angola you increase the angle of
the slope
the friction coefficients forever on concrete is about one third of tensions
as well so the angle is about forty five degrees so if the wrote were forty five
degrees
the card would start of slight
independent of the mass of the court
no matter where it's a truck or whether it is a small court
independent of the with of the tires doesn't entering to its even though you
may think it does
it with both start to slide with the same angle
given the fact of course the same wrote and the same
i first want to
show you some of this
the richest at first very
quality
i don't want it to
become qualitative yet
the difficulty
with these experiments are
i'm going to use this plank here
that's at the moment that my fingers
touched this plank
or touch the bottom of any of the objects that i'm going to slides
all hell breaks loose a little bit of water on the plane
would locally make the friction coefficients locked larger
my fingers gift shop on them
a little bit of chalk on the local place would make the friction coefficient go
down
that's why at this point will keep it
qualitative
the first thing
i wanted to
show you
it's if i take a rubber park
and a quarter of a public park on this inclined
and i have
a plastic bin
she's quite small
acquitted on here
but it's a really intuitive that the friction coefficients
of these plastic bin will be lower
one of the rubble talk so when i think re-use the angle
you expect that first the plastic they will start a slight
the rubble pop and if i gave you the angles at which that happens
you could actually calculated to values
for the friction goldfish
which i will not do not what i will do it later
all i wanted to c i hope
this one will go
earlier than that
from going to increased tilts
woodbury surely i try not to
rock the boat too much
very slowly
it must be approaching
critical angle for the plastic
or it's holding onto itself there it goes
and the rubber gloves
a little later
the rubber
candidate ross
by rubbing it on one side in which case the angle
will be even larger
i told you that the
friction coefficient
is independent
of the mask of the object i have two identical bins here
optus or if they can be identical maybe one of the bombing is a little rougher
than the other
within one hundred to put two hundred grams which is about five times the rate
of the day
and then
within reason when i killed him
they will go at the same angle
because it's independent of the mass
so let's try that again
and see how close they are may be off by half a degree you want to bring of
course
because the plant is not uniform everywhere
promotes eighteen degrees
nineteen and a half
twenty twenty now
twenty-one and your wants twenty one point two
but almost go
at the same time so you've seen that
apparently the mass
very small if any
malcolm something
that i've always find very very moment which is
and that is
surface area
i've two pieces of wood
and there are going to call whatever that means identical you can never make
them exactly the same in terms of roughness
this surface we prepared as well as we prepare these bottom surface with his
bottom surface here is four times small in an area
then this surface here the fact that
i'm going to put the platform
and i'm going to put
the same
object the presents
small ari here
if indeed to friction coefficient is independence
surface area
then when i killed him they should start to slight roughly the same thing
there we go
fourteen degrees
sixteen
eighteen
one goes don't follow switching to tens of a degree
and resume writer lois from different of course the plank
exactly uniform have to be careful
i don't touch the
critical surfaces
so we have seen different temperature coefficients and you have seen
there's almost no effect on
surface area and there's no effect on
on the mass
and that this bos
very unwilling to witness
which of the piles of your car
bus not matter
and that i
asking the question to explain the new assignment number three
why race cars very white parks there must be a reason for that
want you to think about
there is another way
that want to measure the
friction coefficient
which is
way more complicated and really that's not the reason why
want you to see it
the reason why i wanted to
go with me through these argument is that you begin to see house oval
and how really difficult
friction is
i'm going to
puts object now
on inclined began
as we did before
and
instead of having it
stand on its own
i'm going to attach to it
a straight
to view is that object
and here's a strain
anatoly
and he restraint
and here's an all-black mass and tour
these objects
has mass and one
and the angle here
looking for my grandchild i want to do the same colour convention
now
let's look at all the forces that we can think off
here is everyone
that's decomposed that's in the white annex that action
and i will call
is directed why is a warning to perpendicular conspirators
who called his wife
and i was cold this direction
the positive experince
you're free to choose a anywhere you want
force here
and to a jury
and malcolm's a major problem
the biggest problem is
that you do not know in advance
where are the system will start to accelerate in this election
well it will start to accelerate in this election
or whether it will not accelerate at all
it's quite possible
all these three cases as you will see have to be dealt with
independently
you cannot do it
was one equation as you will see
decomposed this force as we did before
in the why direction
so this one
equals and while gene
co-signed all spot
and this bomb x component which is in the minus ecstatic chanel
equals and long
time now
this one n one g coast final thought we never have to worry about there is no
acceleration in the light of action
so is normal force and
will kill the swamp
and it is and long
coastline all to never have to worry about the wider action we notice no
acceleration we only do his forces in the expenditures
without interest
there is a attention
industry
now comes the problem
i do not know in what direction to frictional forces
if these object has the tendency to go appeal which i don't know yet
and a frictional forces in this direction equitable thought is always a
direction with the object wants to go
if however dissolved it wants to go in this direction which i do not know
then the frictional forces the people can disagree
know that
the only thing i do know
is that the maximum value
all the friction
muse static
and which is what we
have dared remember that's me
maximum bellingham but the friction can have
suntan wong g
for turned off
that i know
to know if i want to do is this
i have to
look at it
three complete different situations acceleration in this election
in which the friction this
we can hear acceleration in this direction
in which the friction is pointing their were no acceleration patil
there's also of course the tension here
distension is exactly the same as that tension we discussed that last time i
will not go over that because this is an ideal
and of course on physical situation
before he has no mass
support is completely friction was
and the string
has no match it's a mass was st
and argued last time that therefore
attention here
must be the same as the tension there
with even though the tension
i'm going to evaluate for now only situations that the system
is address
it's not yet
morphing
if the system has been addressed
denotes the end to cheat because these older kids not the story
so we wouldn't know
all situations where the system is address
must be
and two
that's not negotiable this story
as well as a decade
now
i have to
start
splitting
in the following situation
my first auction his that i make the assumption
that the system
chillax
just about to start exterminating reports
it isn't doing it yes
it is just about to do that
if that's the case
then i know
the frictional forces
will be in this direction
and it will have reached
the maximum value
ways the static friction coefficient
now i can write down indy xterra rection
newton's second law
now i have ji which is in the positive direction
minus
and wong
assigned of hot
minus
f max
back now
dot has to be zero
just at the moment that it is just the bulbs
to change his mind and start accelerate
now i hope to use it is and to g
so and to a g
equals
and wild
climb all fine
connection
frictional forces which is this one
through this
just at the moment
that its
wants to start sliding
therefore if i may mass and two
and hair larger
just a hair
and therefore the moment
i made this
largest sign
i'd know that it's going to accelerate upto
that's the criterion for growing uphill
i look at situation to me
now i make the assumption that the object still standing still
is just about to start accelerating downhill
hahaha
if that's the case
i know that the maximum force is now pointing upwards signatures
but it has no different than action
so now i can write down
newton's second law
sort of fictional force is now
helping ci
sonali get g
plus
at max
minus
and wound
krunal thakkar
practical zero
we know that it is
and to a g
so a m two g
equals
and while
sign off on
minus
after next
what is a different as opposed to idea doesn't mind answering here
this is
the object is still not moving
box if i make entombed g their heroics
justice do you remember last
it will definitely start to accelerate downwards
if i make peace
smaller ben stein
object will start accelerating
downhill
this is conditional on this is conditioned to
if the condition is neither want nor too
what you think will happen then
very possible that you don't need any one of these two conditions
we think will happen
thank you
it won't move eight zero
because this this move okays is going to expect government
so in all other cases
acceleration
andy frictional force in this case
really just itself
just the right way
so dat newton's second law
in the expiration
we'll give you for the force
a zero
let us
take a very simple example so that you see this as work
so we have an example here
and in my example
i have a lot of equals one kilogram
and to people's two kilograms
camp that can't make the numbers much simpler
i think all spot
people thirty degrees
archaic
aesthetic friction coefficient
which is all point five
and i take a kinetic friction coefficient
uh... which is a little less which is all point four
question
is it going
federated appeal
accelerated downhill when oil exploration at all
when it comes down to
is that we have to evaluate
three terms
but for state and georgie
and two g
equals twenty will just a clergy ten that is just easier
and while you sign off on
the sign of offer is a hot
so that is fine
and one g
applying all fun
backboard white
and wallet at
maximum
i have to use former friction coefficient point five
i have to use for and what mum you attend and have the coastline
for thirty degrees
and what i find you have to take my word for it
that this is
about four points
and i want to remind you i have used the static friction coefficient decision
opens
i never put a capital and pollutants
because that is very confusing with his normal force all my unit always
aside units of the force is always a new tunes
oc
we were always first-class weather condition while he's met
is twenty
larger
plus four point three three
dot
and the answer is
so we know
that is going to be accelerated
that is not negotiable
so no i could ask you
simple question
what is the acceleration
and what is the tension
and so you will think oh well that was within our reach
not quite
because things are now
going to change
it is going to be accelerated up a hill
then at least know one thing which i'm going to put in
drawing no
i know that this
is the maximum
creeks impossible
which now becomes
new connecticut
because it's going to move
pints and mom
prime g
and co sign off
so that is already won't change
it is moving she was going to be generated
for the frictional forces isn't is a reaction
has the story
so that's why i don't know
newton's second law
in the exploration
so we have to be alternative direction
minus
and one gene
sign off on a
minus is maximum force minus
and one
goldstein all hot
and that now according to a new tunes law must be m wong
eight if a_t_c_ acceleration appeal
one equation was to announce
you don't know any
and you don't know qty
or do you know ki
what history
what is the tension
what is the tension when that thing is being accelerated appeal
anyone
the courage to try
you feed and two g
you couldn't be more wrong
it's not moving into being accelerated
that means dissolved jack is going to be accelerated down
ended this force is the same is this it can never accelerate dob
thirsty must get smaller
remember
an object in an elevator being accelerated down loses weight it's
losing weight
dissolved act must be accelerated all we have to take that into account so
depends who want to start accelerating
real godown so i have a second equation
fallback number two
are called it
the plus direction
sophal tech number two
i have and too
g
minus
equals and too
harmed any
it is very important that you see
that the tension will change
now i have to recreate it was too unknown
now
very easy
this afternoon
and i leave you with that
i'll just give you the results
i find that the acceleration
you cost plus i think three point eight five
that is correct
plus three point eight-point
meters per second script
and i find that the pension equals
twelve point three
notice
i want to add on this a little bit
i find forty acceleration of plus sign
had i found a minus sign
i bought
i'm sure i would've made a mistake violated mandatory that i find the plus
side
absolutely mandatory
who wants to try that
done you save
you said well i would have said it slightly differently
we know that the acceleration is in the election
we'd arrive at there forty acceleration since i pulled up to plus x direction
that was mike plus sign must come out plus
so this comes up negative
you've made a mistake
i'd also want this number to be less den
if not i'd made a mistake while does that number have to be less than twenty
exactly
this object is going down
deported rate reported last night he'd lost weight it's accelerated downwards
his auntie jean which is twenty
bedouins it's frumpy otherwise it would never be accelerated down forties plus
sign is a must
and this is
must and if you find
not of course i go to minus sign you have to go back to your calculations
which have made a mistake
now
we take the same situation
i need everything unchanged but i make the second mass and two
i think it all point four kilograms
so now all the numbers remain the same that we have there
accepted and georgie
now becomes four
now i'm going to test again
is entombed ji which is quarter
is that larger
then five
plus
the frictional forces static
four point three three
the answer is no
going to test for my second case
is and to a g smaller
then five
minus four-point three three the answer
so what do we conclude
what must be our conclusion
condition one has not met condition to was not meant
conclusion this
eight
object
not to be
accelerated
and affection or force is going to adjust along the actual rection so dirty
acceleration indeed
is zero
how does the frictional forces do that
business that slope
you is that object
unruly putting the forces
the eccentric should don't bother about the wider action
i know that there is a patent wonky
side also
and that's wrong is fine
so we have here
component of gravity
which is the m_-one
padmaja
and we know that it is five
whether they're
are also no
that we have tension here
and the tension must be n tool g_e_ because the object is not being
accelerated we back where we work number two is not being accelerated the tension
is twenty
sorry not twenty two two one two and two
attention this
energy is four
five note since downhill *** turns up hill
what will the friction beat how large an important election
apparel
how large
exactly
friction
i would just itself
so if there's a korean
but nothing
all right then i would like to
do a few demonstrations where barry i want you to calculate sheet friction
coefficients fortin
so we're going to put
the particular object
on that's incline
alex was going to raise the angle until the breaks loose
so you should be able to calculate
what the friction coefficient is using deflation tangent awful
people's u_s_
any object that are used for that
is
this
this box
in these boxes a little rates that's not very important
makes the whole thing
three hundred and sixty
long grams
i want you to know that the weights
of this object
if three hundred at sixty-one graham write it down for you here
so the mass of the object
three hundred and sixty one seaward
vacuum certainty is at least one gram
you have to trust me when i give you the angles
i'm going to increase the incline
and the terms of moments
that it will start to slight i'll give you the angle and i want you
to calculate that richard koh
so we're good at first
not ten degrees
twelve nhac fifteen
fourteen fifteen
sixteen
seventeen
fifteen hockey team
nineteen nineteen and a half twenty
twenty degrees
starts to slow
at about twenty degrees write them down
now
i'm going to
do exactly this experiment
robo buoy to supporting
and poured into on this site
and i'm going to go down and two
two points
that it starts to slide a pill
that should allow u
to also calculate
the friction coefficient
you have all the tools for it because once you know
that it is just at the point
of breaking and going uphill
you know that that's equal sign of that equation
holes
and so you should be able to calculate
the friction coefficient
what you'll find exactly the same number as you find from this experiment
not very likely
you have to think about it for yourself
what has grain
the green in this direction could be very different from the grieving
distraction
but it'll be interesting to compare between what you see how much better off
so i'm going to put here this
rope over here
and i'm going to set to be angle now at the given value
so it is it not not negotiable
i said it
that twenty
i could be off by half a degree
again she wants to go just sold at a twenty degrees it wants to go
so uh... i presented from going
and so i'm going to put a little weight on here
novelists
on the grass
and it's not going
and it's a big
is zero
that condition isn't met
and this condition is from now
must ride on your notebook of arnelle independent experiment
equals
quintero
but maybe plus or minus one
i think it's about laundry accurate if i can do
okay i'm going to do a few more weight more mass i should say it and to
and i'll give you the numbers and when he breaks loose you will see it and if
you don't know
i've done that many times
the breaking point is not always at the same last master differ by twenty twenty
five grams easily
so whatever in the movie going to find four and two
i would say
you should at least allow
uncertainty of about something like twenty five grams
just because i don't have many times and i know compete in the worst of times you
may take a quick change in the room
that could change the friction coby
okay we have on the grounds on it
we have two hundred grams on it
two hundred fifty
through sixteen
through seventeen
and goes into second because you go
started to slightly to seven p
for two hundred and seventy grams
i met exactly that condition
which is equal sign
that should allow you to calculate
the static friction coefficient
and you'll get a chance to do that
you stated
assignments
when i have to say not here
and when i was loading these down
making it happen you have here
i hope you realize it at first that want to slide in this election
george first of friction was in this election
that are loaded down more and more
diffraction became less and less and less the closing at the time that the
friction because
zero
i loaded more and more and more
description flips over to the oversight
description friction grows and grows and grows
flight spiro legal battle to not make it go upto
loses the battle at one point
reaches the maximum value i'd put a little bit more all year
and it goes
so this frictional force
is really having a rough time starting off in this direction
slowly becoming less becoming zero changing direction reaching a maximum
and finally
losing the better
friction is often
the pain in the neck as we all know
friction causes where because it's there
it cost you will
car low friction is the road
you pay for that
and people try to reduce friction
barings andrius lubrication
water is an amazing lubricant
it starts raining was a little bit of
dust on the road
the friction coefficient between your party s and erode can become so low
that you begin to
hydroplaned and that you literally
pitcher friction coefficient ghost almost
to zero
to me once and it's no fun
you have to be instantaneously
particularly
when the ring begins in the very early part of the rain
when the wrote this dusty
so you get the water was a little bit of dust mixed very dangerous situation
at home
i have a pen
this is my pen at home actually i have more than one principal belief
this is a very special then
and it is special about it was something that i discovered
purely
accidents
and i want to share with you
this uh...
remarkable
you see when i will take this cover
lot of fiction you can hear it
stops
you can give his life
and so one evening i was born potatoes
and i was looking
xp sp and i walked up to it because i wanted to check potatoes and itouch
tiffin
has no friction
jason spinning and spinning and spinning i couldn't believe my eyes
until i realized
what is happening
what i have accumulated
in the resolve this
the cover was beginning to hydroplaned
on when water in it now
almost don't hear it anymore
is that amazing
almost frictions
so now the water acts like a lubricant
you try visual painted wood working it just the right shaping the divide edge
to win
able to recanted that way
there many experiments that i've done
and many times have been made by people to reduce friction
if you can to avoid contact between two surfaces
that you can do by putting a lubricant in between
but even better it would be
if u could separate the object completely and only have and inbetween
because as much less
well-equipped
it's being done
was great success
people use cover cracks
sorted blow air out from the most of the crash this itself up and now it's no
longer in contact
with the water it's about the war
so he did moves now all it has to overcome
houston air friction
and that's it and that helps tremendously
your will be seeing any
this lecture hall
many demonstrations and i will be doing in the future
reqs what is what i call on an abstract i will show it to you in a minute
it is a long
over the bar for now
cross-section to try to negotiate
and data holding to hear i'd
and we brought here out of that
and on top of that
devices which have been specially designed to protect me fit
this triangle
and then you start blowing the air
they lifted up so they float
and so now when you give them a little
they can move almost not quite that
almost
without friction
islam
lot of fiction
nocturnal
the air
look at the difference
that amazing
exploding all its own air cushion
and i turned it off
moment that the air stops
so this is the technique that is often used
to bill demonstrations if you have to do it in
there is a minimal friction
of course you could do
experiments into shuttle very well where you have
began on the air around
but that's of course a very expensive way
in twenty six one hundred we will use the extract
when we start colliding objects
and try to see what happens before and after the collision
there's a lot of the vice
which is very intriguing
and that's also acts on
the idea that lifts itself up
as a result off
gas
which is flowing out
in this case it's a container of carbon dioxide
carbon dioxide in here which is so late
and there's a small opening here
and this is a
extremely
well machine
flat surface
very flat
and the whole thing
rests on an extremely flat surface
because of the room temperature the carbon dioxide will start to evaporate
and will start to
and therefore under this thing comes a film very thin layer of carbon dioxide
and now you can move this around into our mentioned you not stuck like you
know they have to wonder mention when going back and forced to what we call
the extract now you can move it around
over this whole surface
and that loves you
interesting
thinks
as i want to show you
cosmic dark
refilled attended rutgers solid carbon dioxide
uh... you know solid conduct studied very cold this white stuff is just frost
that's gathered them outside of the camp
don't have to can absorb heat from the room
recovered outside evaporates
and turns into a guest
the guest takes up more room in the solid
so it has to go somewhere
can't come out the top
so it comes out a little hole here in the bottom of the desk
you can see it coming up old
but if i make the point
i think you can see that there's a guest coming out
and blowing plane
note we put to death
with its dream of guest coming up bottom
down on our table top
which is made of a very smooth
piece of plate glass
we can wait a moment our other guests coming out builds up pressure underneath
which it has to do in order to escape
right now to discuss floating on this
film of escaping
effect on the sofa and that i'm sure you can see it from out there a conspiracy
see that pic
see a space between the disconnect last myself
ritual cummock over my shoulder i think i can show you that there is a space
by slipping underneath the desk
this piece of ten for electrical chewing gum wrappers
now will split the temple of the clean the desk
and the plate glass top at the table
showing that there is indeed
a space extend film of gas
between the disk
glass upon which attracts
the purpose of this is simply to reduce the friction to appoint but we won't
have to worry about it or measure it
in our experiments today
it's fun to play with this thing let me show you
i'll give it a little push
just a little one
marigolds
ruling sedately
no sign of slowing up
one back
same thing the other direction
it takes only a very kind of course to started emotion
let me show you that
hide
in
reasonable with something
have a good weekend
you monday