Which Shape CUTS BEST? (Weed Eater Line at 100,000 Frames Per Second) - Smarter Every Day 238

My name is Destin. This is Smarter Every Day. I did a video previously on this channel about how a weed eater line breaks when you go up against something like, I don't know, a chain link fence or something like that.

Aw, that's awesome. That's awesome. But today, I want to address a couple of different things. What do you call this device? I call it a weed eater. A lot of people made fun of me last time. This particular box store calls it a string trimmer. But there's a ton of different things you can—oh what's this? What is this? Google Trend results. Just so convenient that this was here. It looks like most people actually use the same term I do: weed eater. Interesting. If you're up in like, what? Michigan, Pennsylvania, New Jersey, some of those little states, you might say weed whacker. But if you're in Australia or the UK, you might say strimmer or something like that.

Long story short, most people call it a weed eater, which is why I use that term. It's, you know, gener-a-sied. There was a brand called Weed Eater. But anyway, for the purposes of this video, we're going to call it a weed eater. That's how I grew up saying it. And I think that's how you should say it too.

This is one of the most overwhelming decisions for me when it comes to purchasing products for my yard. So, if you think about it, there's a really cool option here. You could get these things to go in the head of the weed eater. Basically, it replaces the auto feed head. These weed eater lines below. My question is, which one should I buy? And there's a lot of different factors like price, durability of the line, things of that. The diameter of the line. I want to look at what cuts best. Because my goal is to cut grass. So it only makes sense to want the shape that cuts grass the best.

And there's a bunch of different options. You got this triangular type stuff. You got this star shaped pattern. You know, there's round. There's square stuff. So today on Smarter Every Day, what I want to do is use a slow motion, high speed camera to look at the very minuscule macro view interaction between a weed eater line—specifically different shapes of weed eater line—and one blade of grass. And we'll see if we can see any difference at all in how they cut. Let’s go get smarter every day.

Goggle up. Except I don't know where my goggles are. I'll find them before we do science, I promise. We're in the garage. And we're going to answer a very simple question. What line cuts best? So if you look right here, it's really, really hard to see. But we've sectioned off little pieces of weed eater line, and we've got them under the microscope.

I'll show you the shapes in just a minute. That's really cool. But look at this. These are the old oscilloscopes that I purchased for the oscilloscope video. It's an oscilloscope music video. I think you'll dig it. When we made that, we got this beautiful cart. And it's wonderful. I can't imagine what a boss you would be like, in the 90s, if you had your oscilloscope on a cart like this. But this is an old Tectronics cart. It has now been converted into—I know. I know. It's great. Yeah. It's been converted into a weed eater approach-o-matic.

And what we've got here. Let me—well, I'll show you the view. We have a macro lens on that camera zoomed all the way in on a single blade of grass. That single blade of grass has a set weight on it. As you know, grass blows over with a weed eater. However, we wanted to have a uniform amount of tension on the grass, so it's a repeatable experiment. So what we're trying to do is isolate all of the variables with the exception of the edge interaction of the weed eater line with the grass.

Trent, chief button pusher for this experiment. Do not let me forget my goggles. That's important. So under the microscope, we have sectioned just a little bitty piece of weed eater line. And we've got it on the microscope slide so we can look at the cross-section. I'm going to back light it. Let’s see. Let’s turn this on. Oh yeah. Look at that.

OK, so this is the first one I've got. It's a round line. It is a—I think the manufacturer calls it a razor core. It's basically just a pure circle with a different density of plastic in the center, right? OK. Let's go to the next line we're going to test. This is a round line that's gray. I think they call this titanium or something like that. But clearly, there's no titanium in this. You'll notice there's a notch on this side. There's a really interesting reason that that exists. I'll explain that later.

All right, let's go to the next one. So this is a triangular line. And this one's called ugly twist, I think. So you can see that it's got a different kind of plastic, or at least a different color plastic on the edges. Let's go over here. Now, this one's interesting. This is a star pattern. I'm going to cut the light off, see if we can—yeah, look at that. Oh, that's cool. We got a weird artifact in our lens there. That's interesting.

What else we have? Oh yup. Here's the round square. I need to focus on that one. Or a dull square. Let's call that a dull square. It reminds me of a cardioid. But it's not a cardioid. And then the last one we have here, this is—we'll call this a sharp square. Let me adjust—yeah. Look at that. It's just like the circular one, but it's got the little edges on the outside. Now let's go do it.

We're going for speed. I found my glasses. Thank you for remembering. So let’s start off with this stuff. Oh, we’ve got to open the garage, right? So we don’t have carbon monoxide issues. OK.

First line is what we call the razor core. I already cut it. It was too far forward. I'm an idiot. Is it focused?

MAN: Yeah, it's focused.

OK, here we go!

OK, slow that down and watch one more time. If you look closely, this is less like a cut and more like a rip. Each blade of grass is different. So we did three tests for each shape. Reviewing these shots one at a time would take forever. So I think the most efficient way to present this data to you is to put all three on the screen and let you make your own qualitative observations.

Next, we went to the gray, round line. Compared to the razor core, the shape and the diameter's pretty much the same. So as you would expect, so were the results. The first time we really learned something interesting was with the triangular cross section. The line is quieter. It's way quieter. The reason the twisted triangular line is quieter is super interesting. If you've ever noticed, some car antennas have a spiral winding on them.

I've been told that this isn't about receiving radio signals. It's about inducing more turbulence, and thus reducing wind noise. The twisted triangle has the same effect. And I assume that's part of the reason the gray, round line has notches in it as well. Who knows, though? That might be just so it breaks more and you buy more line. Anyway, listen to the side by side of the round line and the twisted triangular line and see how much quieter it is.

Oh wow. I expected the triangular line to have a cleaner cut because of the sharper edge. And that’s what you see on the first blade of grass here. But interestingly, not on the other two in this shot.

Yeah, we learned something on the triangle that time. So I've always thought, man, triangle line must be great because it's got that pointy side, you know? But I never thought about one side being flat. And you would have like, a big old smack. It's like, hitting somebody with an open hand versus like, when it hits with the sharp edge, it's like, not only does—

Oh! We need to do this back. Hey weed eater dude! You want to come check this out?

Oh, we could not have planned this. There's a guy that weed eats around here. And he's on the street. He parks on my street.

What's your name?

ROBERT: Robert.

Robert, I'm Destin, man. Nice to meet you. You running weed eaters all day?

ROBERT: Weed eater and lawn mower.

DESTIN: So you’re a weed eater expert, Robert?

I don't know about expert.

DESTIN: How many hours a day do you run a weed eater?

Sometimes, 8-10 hours a day sometimes.

DESTIN: You are an expert. I just made you an expert.

OK.

DESTIN: OK, so the question is, what shape of weed eater line is best? Robert jumped right in and reviewed the high speed footage and started making comments right off the bat. He suggested that we weigh each line in a certain length and calculate its linear density. And he also walked me out to his truck and gave me a piece of the line that he uses every day.

ROBERT: This is $18 a roll.

You've got a sharp square, is what you got.

ROBERT: Yeah.

You've got fancy sharp square. It's like a square that's got a point on each side. Can you see that?

We're going to call this sharp, sharp square. And we also weighed a set length of all the rest of the line. All that being done, it's time to move on and test the star.

This actually surprised me. As you can see, the star line seems to create remarkably clean cuts.

OK, this one's dull square.

From what I can tell here, it seems like dull square rips through the grass, causing it to de-laminate and rip apart vertically rather than cutting straight through it horizontally.

Now we're going to test the sharp square, which is the heaviest line and also has the largest cross section, which makes me think it's going to behave like the flat side of the triangle.

Keep in mind here, we're only doing three tests per line. So this isn't really statistically significant. But you can get a qualitative feel for what's going on here. This seems to be cutting better than some of the other lines, the dull square, for example. But it also seems to be ripping just a little bit. But with this much weight behind the line, you would expect it to go through a lot more cracks.

So this stuff seems to cut cleaner. But see, it's a trade off, right? Because this stuff clearly is more massive. So if I was going up against brush and stuff like that, I would want the massive line.

Let's try what the dude gave us. It's time to test the sharp, sharp square, the line that Robert gave us. And I'd just like to say that, it is interesting to look at yourself performing an experiment. Because sometimes you can easily see your own confirmation bias.

For whatever reason, I had already decided that the sharp, sharp square was the best line. And you can tell that by what I said immediately after cutting the engine off. Clean cut! That's—it's the answer. Turns out the high speed disagreed.

There's a lot going on with this one. It seems like it's both ripping and cutting. But it also doesn't seem to hit the same spot every time.

This line seems to be very stiff, to the point that when it spins up, it doesn't completely flatten out into a disk. One string goes high. The next string goes low. And as you can clearly see here, this often causes it to strike a different position on the grass blade with each rotation.

Also, if you think about the shape of the corner of these edges, it's possible that instead of going through the grass and driving through it like a wedge and blowing the grass apart, it might be pulling it towards the center and making it hit the center of the line.

Sure enough, if you look at the wider slow mo shot, you can see that every once in a while, it will pull away a little plug of grass when it strikes. The star shape seems to be doing something similar. But somehow, it still manages to make a clean cut.

I would love to hear you in the comments tell me what you think is going on. And I'm going to tell you about the sponsor for this episode. And then I'm on to tell you what shape I'm going to buy moving forward. And we're also going to show the slow mo to Robert and see what he has to say.

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All right. Here we go. Time for the results. After running this test, I realized there were things I could have done better. For example, I probably didn't push it in at the same rate every time. I probably didn't push it in fast enough, which means I got partial cuts occasionally. The blades of grass themselves were different.

Overall, this is just not rigorous scientific research by any stretch. But it should arm you with enough information so that next time you're looking at this wall of options, you can make an informed decision. For me personally, if I'm cutting thin grass around the house, I'm going to be using a star shaped line. It's the only one that I saw that actually looks like it's cutting. Everything else looks like it was ripping the grass to me.

Also, the fact that it's smaller seems like it would give me better control. If I was cutting thick stuff all day, or maybe some brush near trees or obstacles, I'd probably go with the sharp square, because it seems heavier and more durable. But it's not so stiff that it doesn't track well. So yeah.

I'm going to go with these two. I'll leave affiliate links down in the video description. You can click those if you'd like to order some line like this. Also, I thought it'd be interesting to leave links to other people's tests and what they think. To round out the video, I'd like to show Robert the slow motion of the star shaped line as well as the sharp, sharp square he provided to see what he has to say.

The sharp, sharp square?

Exactly. He already knows—the already knows the lingo, man.

I observe things.

What do you think?

I think this right here, being a smaller in diameter is giving you the cleaner cut, which I think possibly is creating a few more revolutions out of the weed eater.

Oh, because it has less drag.

Yeah. Less drag.

So it's faster.

Maybe a little faster.

Why don't we hire Robert to make this video? I think you're right? And also the—I think the bigger stuff that you're using, I think it's tougher. I think you could like, get in the bush with it.

Yeah. Yeah we tear up some stuff with that.

So it’s a trade off. So if you're like in a dinky residential, like, I'm just going to do this next to my flowers, you could probably use something like that. Go really fast and just like, more precise. But if you're getting in the thick of it, use the big stuff.

Yeah. If you're getting into some stuff under some trees. I'd like to see it on YouTube. I mean I can just go ahead and subscribe.

It's called Smarter Every Day. I just convinced Robert to subscribe. Did you subscribe?

I subscribed.

DESTIN: All right.

ROBERT: And I will like and share.

Robert's with it, man.

Yeah, is this it right here?

That's it, yeah.

OK. All right. Subscribe.

I'm telling you, man. Alabama people are with it.

Some of us are. I'll get a notification, I guess, when you put—

Yeah.

ROBERT: --something new on there.

DESTIN: You'll get a notification if you hit the bell.

ROBERT: Yeah. Let me hit the bell.