Hey, it's me, Destin. Welcome back to
Smarter Every Day. It's time for the
Weed Eater episode. And the way-- I wanted
to shut the door. The way you can tell
that I've staged all this is that this Weed Eater's
going to crank up immediately. But here's the deal. When it comes to
operating a Weed Eater, I have a mental model in my head
of how the Weed Eater works. Like, as it goes faster,
it slings out these lines in a disk, right? But is the disk
like a solid line pointing straight out
from the Weed Eater head? Or I guess you could
call it the trimmer head. Or is it more like
a lagging wave? I don't know. Check this out. [REVVING MOTOR] Let's look. So if I'm going to weed eat
this whole spot right here, I rev up the Weed Eater. But when I don't rev
up the Weed Eater, you can see that
the line is lagging. It's all curled up. So at some point in
there, it straightens out. Then I can go in. I can trim. And for some reason,
I feel like I should trim
from right to left. I don't know why, but it
just feels like that's something I should do. Let's go over here to this. Watch this. If I come down,
should I plunge? You see that lays the grass
down in a certain way, but if I go like
this, it doesn't? I don't know. My point is there's
a lot of physics in how Weed Eaters work. And there's these
quantitative things that we should be
able to measure with a high-speed camera. But there's these
qualitative things that you just know if you spend
time running a Weed Eater. So today on Smarter
Every Day, I want to take that internal mental
model of how Weed Eaters work that I've developed
over years and years of running Weed Eaters. And I want to test it
with a high-speed camera to see if we can understand
the physics of how
a Weed Eater works. Let's go get
"Smarter Every Day." [THEME MUSIC] What up? TRENT: What's up, man? DESTIN: Trent is
going to be the trigger man on the slow-mo camera for us. So I'm going to be
running the Weed Eater. And I'm going to get that
Weed Eater head positioned over this X right here. And we're going to use
this Phantom v2511. We'll record it at about I'd
say 12,000 frames per second. And then we're going to see if
the Weed Eater line slings out or, more accurately,
see how it slings out. Because if you think about
it, as the line is whipping through the air, you
have aerodynamic drag acting on the Weed Eater line. But you also have the
angular acceleration slinging the line out. So you've got this
balance of forces. That being said,
the question is, does the line ever
truly get straight? Because in my head, I'm
operating with a disk with straight lines out of it. 12,000 frames per second. OK, ready on trigger? TRENT: Yup. DESTIN: Here we go. Ha! [REVVING MOTOR] Ready? TRENT: Yup. DESTIN:
It's a simple test, but it should show us exactly
how that straightens out. All right, so as we
speed faster and faster, you can see that the
line is lagging behind, probably due to that drag
that we talked about. But there's also still a little
curl at the end of the line, probably because it remembers
being wrapped around a spool. My question is, if we
make the line even longer, will this drag be
even more pronounced? Meaning, would it lag
behind even further? There's only one
way to find out. We got to test it. If we were to remove this
guard-- don't do this at home, all that stuff-- I think what would
happen is we would see that the
aerodynamics would start to win, like the drag
on the line, right? Here we go. Let's do this. [LAUGHING] It's hot in this helmet. [REVVING MOTOR] It's going to hit my knee. So I'm learning
all kinds of stuff. Like, the torque
demand on the motor is a function of the length
of the line and the
aerodynamic drag. So for example, while he's
saving that high-speed file, listen to this. [REVVING MOTOR] It doesn't rev all the way up. Right? But if I cut that
line off... [REVVING MOTOR] I never thought about that. Huh. TRENT: This looks so Alabama. DESTIN:
That's a good thing. It's like The Stig. This is the Alabama
version of The Stig. Roll tide, baby. So once the Weed Eater line
gets to a certain length, the aerodynamic drag
is just too much, and the whole system
lags significantly. But Weed Eater
designers were clever, and they integrated a
really interesting tool to make sure the line
both stays balanced and at the optimum length. There's a feature
in a Weed Eater where you can tap the
head down on the ground. You hit the button at the end,
and it will release more line from both sides of the spool. There's also an integrated
blade in the guard itself. So when the line
gets long enough, it will trim the weed eater
line to the right size. But I've always wondered
how that cut takes place. This is an older Weed
Eater I've had for a while. And I don't expect it
to make a clean-cut. But I want to use the
slow-mo camera here. And Trent was pretty smart
and came up with a mirror to bounce light up in
there so we can see it. So let's see what exactly
happens when we bump the line and get more. We'll see what that
cut looks like. [REVVING MOTOR] TRENT: Good? DESTIN: Yeah, got it. There's so much to see. So it's not a single cut
like I've always thought. It's like a continuous
whipping until it pulverizes it into the right length. The torque on the
engine is a function of the length of the line. The line is determined by the
position of the knife blade. The balance is determined
by both sides of the line being equal. It is time to cut grass. Let's go cut grass. TRENT: Ready? DESTIN: Yup. [REVVING MOTOR] OK, I've got a theory that there
are different types of grasses that behave differently. Like, that was a blade of grass,
and it kind of de-laminated. When it started getting
hit by the thing, it started ripping apart. But if we go over here
to something like this that's more of a
stalk-y type of grass-- I don't know if
you can see this. I wonder what's going to
happen there, because it's going
to rip differently. So let's see if we can
get a slow-mo of that. TRENT: Ready? DESTIN: Look at this. You've got a stob. That's a grounding rod. So let's replicate that. We've got a metal stob
right here in the ground, and it's hammered in. I've noticed that
when I'm weed eating and I hit something like that,
it'll pull my Weed Eater in. OK, here we go. I always thought that
hitting an object like this would pull the Weed Eater
directly towards the steel rod. But if you look closely,
you can see that it's a little
different than that. The line is hitting
the top-right side of the steel rod. And you can tell this by the
way the line wraps around it. It almost makes it
look like a pulley. If you were to draw a line in
the direction of that force, you can see that that's the
direction the trimmer head gets pulled. Just play it forward,
and you can see that it kind of
follows that line. So it's not being pulled
directly in like I thought. It seems to be reacting
to the force that's being applied to that rod. All this happens
so incredibly fast that I never thought about
what was actually happening. OK, the next thing we're
going to talk about is what happens when a Weed
Eater goes up next to a fence. Over here, a long time
ago I had an idea. I wanted to create a
little gourd garden. And so I put this wire
fencing, if you can see that. I put this wire fencing up
next to this wooden fence. Now, over time for some
reason I came out here, and I'd weed eat this thing. And it would break
my Weed Eater line. And I got tired of that. So I just quit Weed Eating it. So now we have big 20-foot
trees and stuff like that. So to try to understand
why I got frustrated and quit weed eating
that stuff, we have set up a Weed
Eater obstacle course. We've got chain-link fence here. We've got what I call
"hog wire" here, which is maybe
not quite hog wire. But it's a pretty stout
wire, but it's still not quite as strong as
the chain-link fence. And then we've got
this other one. It's a smaller
diameter fencing here. So the idea is with the
stob, the Weed Eater line would rotate around
that stob, right? And it would act like a pulley. If we have a smaller diameter
here, does it do that? Or is the minimum bend
radius a lot smaller, and will it just cut it? OK, it feels more like science
if we take some measurements. So looks like about 0.110,
0.112 an inch on the chain link. And let's look at the
Weed Eater line itself. Looks like we're around
0.095 of an inch. [REVVING MOTOR] Yeah, it definitely
pulls it to the side. The question is
what is the interaction of that Weed Eater line
to the fencing look like? Aw, that's awesome! [CHUCKLING] That's awesome. So it wrapped around it. And at times, it
doesn't break it. And at other times, it does. Oh, what happened there? Oh. TRENT: [CHUCKLING] DESTIN: OK, if the Weed
Eater line wraps 360 degrees around the fencing, then it-- is it a tension break? It rips it. TRENT: Wow. DESTIN: Oh! OK, cool. So it's like a spaghettification
of the Weed Eater line. It wraps around the fence. And then if it goes 360, it
has to unwind the whole thing. And sometimes it's
easier just to break. I can't tell if it's a tension
break or a sheer break. Because the chain-link
fence is on a diagonal, it looks like as the Weed
Eater line comes in and hits the fence,
it funnels it to the corner. And because there's another
wire going through the corner, it's like a pinch point. I bet if we go to the
smaller diameters-- yeah, if we go to the
smaller diameter wires, it's going to have a
smaller radius of curvature it has to bend around. Mm. Mm. Interesting. We need to move on
to the next one. What I'm calling hog
wire is about 0.085. [REVVING MOTOR] It definitely grabbed more. And you can see that there
are some tension issues there. It's trying to pull. The brake is very
different than I thought. It's a tension break, at
least on this, because it seems like it's wrapping. And it's pulling so fast. It's unwrapping it
so fast, like a whip. And it's a tension break. So there you go. We've learned something. If it goes around
360 degrees, then it has a really tough
time recovering. Also, this has got to be
different with a square line or a triangular or
a polygon-type line. We're going to do another
video following up on this with different
types of Weed Eater line. OK, here we go, time
for the small stuff. This is 0.060 of an inch. This is smaller than
the Weed Eater line. Let's do it. [REVVING MOTOR] TRENT: Whoa! DESTIN: Yeah, that's-- TRENT: That was scary. DESTIN: That's scary,
but that's-- that's what it's like to weed eat-- that's
why you always sneak up next to the fence, because you're
worried that it's going to grab your Weed Eater and go. OK, it broke at the
welds, which makes sense because when you
weld wire like that, there's a heat-affected
zone on that wire. So right there, I would
expect right near the weld to be the weakest
part of the wire. This didn't break. Wow. This episode of
Smarter Every Day is sponsored by Raycon earbuds. I'm going to show you
my everyday carry stuff. Every morning, I wake up, I get my multi tool,
my phone, my wallet, and I get the Raycons. I throw them all in my pocket,
and then I go start my day. But the Raycons are the
most interesting thing to me because they have
this little case-- sorry, I just got
some grass in there. They've got this
little bitty case that charges these earbuds. And they pair seamlessly
with the phone. It's really impressive. These are called the
E25s, the Everyday E25s. And what's so cool
about them is you get six hours of
play time on these, and they don't
cost a lot at all. These things start
out at half the price of the other top
premium audio brands. And they sound just as awesome. I like them so much-- these are mine-- I've
had these for months-- that I reached out
and I purchased these. This is the E55 Performer. I paid for this with my
money because I wanted them, and I wanted them in blue. This is what I was
super excited about. I just open these things. I have not tried them yet, but
these fit really, really good in the ears;
check this out. It's pretty cool. So they just go right there-- boom. You can run in them. I used them to weed eat, mow
the yard, things of that nature. They're fantastic. I haven't tried these E55s yet,
but I certainly love the E25s. Now, these they sent me because
I'm doing this ad, right? Like, I didn't pay for these. I did pay for these because
I like these so much. So if you want to
check this out, go to buyraycon.com/smarter,
and you can get 15% off. You will like them.
You will enjoy them. Most importantly, if
you lose these things, that's not the end of the world. They're priced right in
that right sweet spot. You get four charges
out of the little pill. You get six hours on this thing. You're going to dig them. That's it. Buyraycon.com/smarter, 15% off. [THEME MUSIC] I hope you enjoyed this video. I've heard people
my entire life say, oh, triangular Weed
Eater line is best. Square Weed Eater line is best. Twisted square is best. Round is best. We're going to solve that. We're going to test them
with empirical tests. So we're going to have data. We're going to
answer the question, "What is the best
Weed Eater line?" If you would like
to see that video, please feel free to subscribe
to Smarter Every Day by clicking the little
Subscribe button, maybe even the bell. If not, that's no big deal. I hope you enjoy your summer
out weed eating the yard. I know I am looking
forward to it myself. Go get some vitamin D. Anyway, that's it. I'm Destin. You get "Smarter Every Day." Thanks for subscribing,
maybe, if you feel like this video earned it. If not, that's cool. Have a good one. Bye.
I love these fun summer videos we've been getting. Last week we got Mark Rober about Squirrels, then CGP Grey talked about being a pirate on the open seas with friends, and now Destin with weed eaters
When I worked at a cemetery, we didn't use the guard and string cutter so we could run with longer strings, for a bigger cutting radius. All else being equal, the bigger radius means faster speed at the tip of the string.
When the machine is properly controlled, only the very tip of the string does any cutting or touches any surface; we got skilled to the point that the string barely touched the stones, otherwise you burned through a spool of string very quickly.
The machines that had old blown out mufflers were very loud, but they had more power and you could run with longer string. If you let out too much string and the motor bogged down, you could just hold the cutting head near a corner of a gravestone and it would cut the string to whatever length you wanted. Thinking back now, I believe we may have removed the mufflers on purpose even... Good thing we wore good ear muffs.
Loved the video apart from 1 thing, The measurements were all in imperial. Is there any chance that you could have a pop up on screen or an overlay or something to state the metric equivalents. This would make the video more accessible to a larger audience.
Destin, if you see this, this video was fantastic. What stood out to me the most, interestingly, was the audio. The audio from this footage was nothing short of a foley artists dream come true. At the speed you presented the footage, the sound from each collision seems so well isolated and suitable for so many creative applications.
You may even have enough material for the next mortal combat game! https://youtu.be/IYS0rPYjW28
It was surprisingly brutal when the line absolutely shredded that blade of grass, there was just so much more force behind the line than was necessary to cut the grass.
(I also paused at 14:35 to read the message. I can't wait to see the different shapes ^_^)
I realize the next vid is probably already filmed but a cool youtube channel called Project Farm examined the durability of weed wacker lines. Could be cool to see a collab at some point. Is there anything more fun than garage/backyard science?
This video really drove home to me how long we've been putting microplastics in the environment. I'd been thinking about this more than usual after the recent study showing microplastics in the GI tracts of birds of prey, and thinking about the sources of these plastics. I've been using weed eaters for decades and never noticed the plastic debris when I'd hit a sprinkler head or similar.
I'd thought of the microplastics issue as being much more modern than this showed it to be.
So apparently weed eater is the term most people use. I feel like my whole life has been a lie.
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