High Speed Videography The Time Microscope
when i was an undergraduate
i was fascinated by how within a single
drop of pond water
i could see numerous alien looking
organisms with diverse ways of swimming
around
and capturing prey in the same way that
the microscope allowed us to rediscover
biology
at a different size scale i believe that
the high speed video camera
allows us to rediscover biology at a
different time scale
in a way the high-speed video camera is
a sort of microscope
into time the best part about this is
that while the microscope has been
around since the 16th century
the high-speed video camera has only
been used to study biology for the past
20 years
this is due to innovations that allow
for the filming in low light conditions
this means that we can film organisms
without frying them
but what this all means is that there
are a bunch of discoveries yet to be
made
by looking at the world to the lens of a
high-speed camera today i’m going to
share with you some of these discoveries
as a member of the paddock lab i was
able to be a part of a project that
looked at the jumps
from the larva of a fly specifically the
gall midge fly
you can view these larva as squishy
grains of rice that curl up then rapidly
uncurl
to fling themselves into the air here’s
a video from my colleague’s paper
showing their jumps
in the second video i’m going to show
you a more close-up video of this
take-off sequence
now this entire take-off sequence only
lasts one millisecond
just for comparison the average blink of
an eye lasts anywhere between 100 to 150
milliseconds
literally blink and you’ll miss this
incredible motion
but this time microscope is not only for
animal motions
we can also aim this time microscope at
the plant world
here are some common weeds found in
north carolina and other parts of the
united states
in red we have the wood sorrel and in
yellow we have the hairy bitter crest
while seemingly boring at our time
scales we can we can look
at these fruits under the thai
microscope to capture a remarkable event
seed dispersal first i’m going to show
you
uh the seed the seed dispersal of the
hairy bitter crust
fruits with this plant explode showering
the surrounding area
in confetti like seeds the cool thing
about this motion
is that the explosion of one fruit leads
to the explosion of other fruits in the
plant
next i’m going to show you the sea
dispersal mechanism of the wood sorrel
you can view this mechanism this
mechanism reminds me of those small
rubber rubber toys we had when we were
young that you can flip inside out
put in your palm and watch as they pop
into the air in the same way the
membrane surrounding each seed inverts
setting the seeds out here’s what i mean
and in case you didn’t catch those two
there’s one more seed so if you pay
attention to the center of the fruit
you can see one more right there
so again both of these really awesome
motions are
way too fast to be seen by the naked eye
and without the high speed camera we
would have missed them
all the motions i shared with you so far
are examples of ultra fast motions
just so you can appreciate how fast
ultra fast is i’m going to compare them
to some more common examples of fast
organisms
when we think of fast organisms we
usually think of sprinting cheetah
the diving falcon or the swimming
sailfish
let’s compare these fast organisms to
the ultra fast
and i’m going to use a metric called
acceleration acceleration is a
measurement of how long it takes to
speed up
so above these fast organisms we have
the acceleration of a formula one race
car
above this we have the acceleration of a
missile and here is where we begin to
see
the accelerations of ultra-fast
organisms remember that squishy grain of
rice that jumps
that gauntlege larva has takeoff
acceleration similar to that of a
missile
above that we have the accelerations of
seeds shot from the wood sorrel
and above that we have acceleration of a
bullet shot from a gun
now what organism could possibly have
accelerations similar to a bullet shot
from a gun
this is the range of accelerations of
the mandible strikes of a trap triangle
and this is the organism that i wanted
to study
traptor ants are large ants with animals
that they can snap shut at incredible
velocities
here’s a video i took while collecting
these ants in florida
this is taken in real time ant crawls up
the leaf senses my finger
and snaps sending it backwards i’ll play
it one more time
the ant crawls up the leaf senses my
finger snaps and almost seems to
teleport backwards
without the high speed camera we can’t
really see what’s going on here luckily
we can put this motion under the
under the time microscope i’m about to
show you a video that’s
that’s filmed at 210 000 frames per
second
just for reference my iphone’s slow-mo
camera films at only 240 frames per
second
the video i’m about to show you is 800
times slower than the iphone slo-mo
video
and here it is
what i want you to notice is that even
when filming at these incredibly high
frame rates this motion is still pretty
fast
and what i was interested in was what
happens during the impact of one of
these strikes what happens when one of
these mandibles
strikes target such as my finger in the
previous video
the reason why i was interested in these
impacts is that while dr adrian smith
and i were collecting these ants in
florida
we saw these ants use their mandible
strikes against so many different
targets
we saw him use demandable strikes to
pick up small prey items like termites
we use them use their mandible strikes
to pierce the cuticle to subdue large
pre-items like grubs
in this third video my favorite video
you can see an ant go up to a beetle
strike the beetle and fling itself away
another ant goes to the beetle strikes
but anchors itself
another ant goes up the beetle strikes
the beetle and this time pushes it away
from the nest
from these videos you can see ants do
these mandible strikes for predation
for defend for defense to even use these
mandible strikes to jump
here’s a video i took the ant aims
mandibles towards the ground
strikes the ground and flings itself
multiple body lengths into the air
they use these mandible strikes to
escape from the dangerous ant line pits
dug in the sand
here’s a video from that paper
so across all these diverse uses you can
see why i was interested in finding a
way of measuring the impacts across
these different scenarios
for inspiration on how to measure these
impacts let’s look at other
fast biological motions and how
scientists have studied them
i’m going to be comparing these motions
to the blink of an eye
in red we have the contact duration
between a cheetah paw and the ground
during a sprint
this is anywhere between 50 and 80
milliseconds
and this has been measured with a load
plate
next we have the impacts between a
woodpecker beak and a tree
scientists have used a load cell to
measure these impacts
what about a more human example
dangerous uh
impacts between football player helmets
is anywhere between 5.5 to 13
milliseconds
scientists have used accelerometers
placed inside the helmets to measure
these impacts
so where’s the trap joanne strike in all
this
this tiny purple sliver is the duration
of a trap giant strike
at 0.13 milliseconds this has been
measured with a high speed camera as i
showed you a couple slides back
and just for comparison 800 of these
strikes in real time can be played back
to back
in the time it takes to blink but this
wasn’t what i was interested in
what i was interested in was the impact
from one of these strikes which is a
much shorter duration
so in order to put the impact from these
mandible strikes on this graph
we have to call it our magnifying glass
this this this the same purple rectangle
from before
indicating the duration of a trap to ant
strike this yellow sliver
is a duration of a traptor ant strike
impact at 0.005
milliseconds or one frame when filming
at 210
000 frames per second just for
comparison 20 000
of these impacts can be played back to
back in live in real time in the time it
takes to blink
for strikes at this size and this time
scale we really have no device to
measure these
impacts so it seems like our time
microscope has temporarily failed us
so how can we measure something that can
be measured with a high speed camera
the answer is with perseverance and a
little bit of creativity
while i was thinking about this question
all’s filming and striking targets
different targets
here you can see an ant striking a
plastic target the ant strikes the
target
and both the target and the ant are set
in different directions
this motion reminded me of newton’s
cradle a popular dash toy where you lift
one ball up
let it go and the ball hits other balls
in the sequence
in the same way i figured that we could
capture all the energy
released by this ant in that tiny tiny
amount of time
by measuring the target and the ant
after the strike
so all i had to do was mount the ant and
the target from pendulum
this is much easier said than done my
tears on my prototypes in my first
prototype i suspended both the ant
and the target from here it sounds silly
i know but when you consider the mass of
an ant
you need a similarly lightweight and
sturdy string
i just see from this video when the
answer has a target it seems to bob
around and
then turn around too much this wasn’t
too good
next i mounted the ant and the target
from a carbon fiber rod
and while it’s not depicted in this
video uh the carbon fiber rods are
attached to a roller bearing
an air roller or a ball bearing i’ll get
more i’ll get more
uh i’ll talk more about that later you
can see from this strike the ant strikes
the target
and seems to wobble the target seems to
wobble a little bit too much
i think this wobbling is due to too much
friction at the point of rotation so let
me talk more about that
at the point of rotation as i said
earlier i use the ball bearing
ball bearings use small metal balls to
facilitate the motion of the inner part
and the outer part these are found in
skateboards and roller blades
and while they work for rollerblades and
skateboards at the size
size scale of an ant they seem to stick
a little bit too much
so i was a bit stumped here until i
found about these really cool devices
called air bearings this is a video from
the website
instead of using metal balls to
facilitate the motion of the inner part
and the outer part
air bearings use a pocket of air you can
see from this video
that air is fed into this bearing and
allows for almost near frictionless
point of rotation
i incorporate these bearings into my
setup to produce this final setup shown
here
from this setup i was able to get videos
like this that are really smooth and
easy to interpret
in the first video you can see an ant
striker target that is mounted on a
pendulum
and in a second video you can see an ant
strike a target that is stationary
so an added benefit of this setup is
that allows me to test different targets
that i can swap out
so why build a pendulum for ants again
remember earlier i said that chapter
ants use their mandible strikes in so
many different ways
in a way i kind of view these animals
mandible strikes as a sort of multi-tool
they use these strikes to strike small
squishy targets to strike large squishy
targets
to strike large immovable targets like
the ground
and even weird substrates like sand
before this device we had no real way of
measuring these impacts across these
different scenarios at this size and
time scale
however with my pendrive setup we are
now equipped to find the pros and cons
of using lightweight high acceleration
impacts
so today i only share with you one
discovery to be made by looking at the
world through the lens of a high speed
camera
but remember earlier i said that there
are so many discoveries to be made still
for example here are some videos from
from the lab that i didn’t even get to
show you today
behind each of these videos is a story
similar to mine of curiosity
and discovery these videos span fungi
plants and animals so i hope from this
talk
you can understand why i’m so excited
for discoveries yet to be made by
looking at the world through the lens of
a high-speed camera
thank you
you