[Music]...   [Sneeze]
[Record skip sound] Hey!
I'm so sorry...
Oh, oh my God, oh that's disgusting! Eww.
What if he had a cold? Am I next?
[Sneeze] During flu and cold season,
you might notice a lot of sneezing going on.
Viruses, like those that cause colds and influenza,
rely on sneezes as a sneaky way to spread.
They hide in mucus droplets
that can end up  on the surfaces that you touch.
Or even directly on you,
if you happen to get in the way of the spray.
So, how far away do you have to stand
to make sure you stay safe?
Time to Science!
[Snazzy background music]
Sometimes when you sneeze a fine spray comes out.
Other times big old thick boogers come flopping out.
These thicker boogers have a higher viscosity,
a measure of how thick and viscous a fluid is,
both thick and thin sneezes can spread germs.
But how does the viscosity of a sneeze
affect how far it spreads?
To find out we need to do an experiment.
First we need a hypothesis
or a prediction that we can test.
This prediction will compare a variable,
something that changes,
against a control, or something that stays the same.
In our case we want to compare thick vs thin nasal goo.
My hypothesis is that thick viscous slime
will spatter less and go less far than thin snot will.
But how are we going to test this?
No two sneezes are alike after all.
In this case, we can actually simplify this down.
We're going to create a model, a representation
of something that happens in the real world.
We're going to use this little dropper
as our artificial nose.
We'll fill it with our fake snot
and squeeze the bulb to make the snot fly.
To measure just how far it goes
we'll squeeze this bulb and position it over a long tarp --
which I've marked out in centimeters and meters --
to show just how far our snot rockets fly.
For our thick fluid I found a recipe
using corn syrup and gelatin.
It creates this nice, gross, goopy mess.
Snot is actually a mixture
of water with sugars and proteins.
So corn syrup and gelatin are a pretty good stand-in.
For thin snot I'm just using colored water.
For each type of snot, we load up our droppers,
smack the bulb, and watch the fluid fly.
Then we measure how far it went.
We can also divide up our tarp into sections
to find out where the fluid concentrates
for each kind of snot.
This will allow us to create a graph called a histogram.
But hold on a second, we just did that once,
that's not enough.
If we want to learn about sneezes in general,
we need to run this a lot more times.
How many times?
I need to do something called a power analysis.
The math behind this can get a little complicated,
but I use this handy table.
It tells me that in order to compare the differences
between my two types of snot --
I need to run each kind 26 times.
Better get to it!
[music]
Phew. Now we've got all our data
and it's time to group it together to find the mean,
or the average, for the thick snot and the thin snot,
to find out how far they flew.
Then, we'll run a test called a t-test.
This is a statistical test that we can use to determine
if the distance that the think snot and the thick snot flew
was different enough to mean anything.
[music]
My t-test shows that yes, these are different.
My viscous snot also concentrated much closer
to the sneezer than my thin snot did.
And my effect sizes show that these differences
are very large indeed.
When conducting scientific experiments
it's important to compare results.
Have other scientists studied snot? What did they get?
Well, a 2016 study showed that larger snot droplets
spray an average of two meters.
While smaller ones can spray up to 8 meters, or 26 feet!
A 2005 study also showed that
increasing the cohesion of mucus droplets,
making them stick together and glop more,
actually decreased the distance
that the mucus could travel
and made it less easy to hit a target.
How did ours compare? Well,
our mucus didn't fly quite as well as the 2016 study.
But, that could be because
our tiny dropper isn't a good substitute for a nose --
and squeezing the bulb isn't exactly a strong "Achoo!"
But we did show that changing the viscosity of our fluid
decreased the distance that it could go,
like the 2005 study.
Keep in mind that most sneezes are a mixture
of thin snot and thick snot.
So, stand well back regardless.
And the best way to stop a sneeze's spread
is to cut it off at the source.
So sneezers, cover your nose and mouth,
and wash your hands.
Anything else is snot cool. [laughter]
Do you have any experiments you want me to try?
Leave your ideas in the comments,
and don't forget to *subscribe*
for more awesome experimental videos.
And, if you want to perform this experiment yourself,
head over to "Eureka! Lab," where you can find
the full description of how to perform the experiment
and all the analyses.
The links are right down below.
And thank you so much to Matt Hartings
and American University
for lending us this awesome lab space!
[music]
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