ClassX Video Lessons Youtube Channel SmarterEveryDay How Weed Eaters Work (at 62,000 FRAMES PER SECOND) – Smarter Every Day 236
Hey there! Welcome to an exciting exploration of how weed eaters work. Have you ever wondered what happens when you rev up a weed eater and start trimming the grass? Let’s dive into the fascinating physics behind it, with some help from high-speed cameras!
When you start a weed eater, the line inside spins rapidly, creating a disk shape. But is this disk a solid line or more like a wave? That’s what we’re here to find out. As the weed eater speeds up, the line straightens out due to the forces acting on it, like aerodynamic drag and angular acceleration. These forces balance each other out, but does the line ever become perfectly straight? Let’s see!
To get a closer look, Destin and his friend Trent use a high-speed camera that records at 12,000 frames per second. This allows them to see how the weed eater line behaves as it spins. Initially, the line lags behind due to drag, and there’s a slight curl at the end because it remembers being wrapped around a spool.
What happens if the line is longer? The drag becomes more noticeable, affecting how the weed eater performs. Designers cleverly added a feature where you can tap the head on the ground to release more line, and a blade in the guard trims it to the right length.
Destin notices that different types of grass react differently to the weed eater. For example, a blade of grass might tear apart, while a stalky type might rip differently. This is because of the way the line interacts with the grass, and it’s fascinating to see in slow motion.
When a weed eater hits an obstacle like a metal rod or a fence, it behaves in unexpected ways. The line might wrap around the object, creating tension that can break it. This is especially true with fences, where the line can wrap around the wires and break at the weakest points.
Destin plans to test different types of weed eater lines, like triangular or square lines, to see which works best. This will help answer the age-old question of which line is the most effective for trimming.
Weed eaters are more than just garden tools; they’re a blend of physics and engineering. By understanding how they work, we can use them more effectively and appreciate the clever design behind them. Whether you’re trimming grass or tackling tougher weeds, knowing the science can make the job easier and more fun!
Thanks for joining this exploration of weed eaters. Keep learning and enjoy your time in the garden!
Gather materials like a small motor, a battery, and some string to create a mini weed eater model. Experiment with different string lengths and observe how they affect the spinning motion. Discuss with your classmates how the forces of aerodynamic drag and angular acceleration are at play.
Use a smartphone or camera with slow-motion capabilities to record a weed eater in action. Analyze the footage to observe how the line behaves at different speeds. Share your findings with the class and discuss how the line’s behavior changes with speed and length.
Collect different types of grass and test how each reacts to a weed eater. Record your observations on how the grass tears or cuts. Present your results to the class, explaining why certain types of grass might react differently based on their structure.
Create a small obstacle course with materials like metal rods or fences. Use a weed eater to navigate the course and observe how the line interacts with obstacles. Discuss strategies to prevent line breakage and improve cutting efficiency.
Test different shapes of weed eater lines, such as round, square, and triangular. Compare their effectiveness in cutting grass and handling obstacles. Write a report on which line shape you found to be the most efficient and why.
Sure! Here’s a sanitized version of the transcript:
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Hey, it’s me, Destin. Welcome back to Smarter Every Day. It’s time for the Weed Eater episode. I wanted to shut the door. The way you can tell that I’ve staged all this is that this Weed Eater is 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 it works. As it goes faster, it slings out the line in a disk shape, right? But is the disk like a solid line pointing straight out from the trimmer head? Or is it more like a lagging wave? I don’t know. Check this out.
[REVVING MOTOR]
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 it up, you can see that the line is lagging. It’s all curled up. At some point, it straightens out, and then I can go in and trim. For some reason, I feel like I should trim from right to left. I don’t know why, but it just feels like 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? My point is there’s a lot of physics in how Weed Eaters work. There are quantitative things that we should be able to measure with a high-speed camera, but there are also 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 them, 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. 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. We’re going to use this Phantom v2511. We’ll record it at about 12,000 frames per second and then see how the Weed Eater line slings out.
As the line is whipping through the air, you have aerodynamic drag acting on it, but you also have the angular acceleration slinging the line out. So you’ve got this balance of forces. 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.
[REVVING MOTOR]
It’s a simple test, but it should show us exactly how that straightens out. As we speed up, you can see that the line is lagging behind, probably due to that drag 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? 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. [LAUGHING] It’s hot in this helmet. [REVVING MOTOR] It’s going to hit my knee. So I’m learning all kinds of stuff. The torque demand on the motor is a function of the length of the line and the aerodynamic drag.
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.
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 stalky 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. A long time ago, I had an idea. I wanted to create a little gourd garden, and so I put this wire fencing 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. I got tired of that, so I just quit weed eating it. So now we have big 20-foot trees and stuff like that.
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. Then we’ve got this other one, which is a smaller diameter fencing.
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. 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 does 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 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. 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 break 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 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 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 playtime 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 opened 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 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.
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Let me know if you need any further modifications!
Physics – The branch of science concerned with the nature and properties of matter and energy. – In physics class, we learned about the laws of motion and how they apply to everyday objects.
Forces – Pushes or pulls that can cause an object to move, stop, or change direction. – The forces acting on the car included gravity, friction, and the push from the engine.
Drag – The resistance force caused by the motion of a body through a fluid, such as air or water. – The engineers worked to reduce drag on the airplane to improve its fuel efficiency.
Acceleration – The rate at which an object changes its velocity. – The car’s acceleration increased as the driver pressed harder on the gas pedal.
Camera – A device used to capture images, often used in scientific experiments to record observations. – The scientist used a high-speed camera to capture the rapid movement of the chemical reaction.
Grass – A plant that is often used in scientific studies to understand ecosystems and photosynthesis. – The biology experiment involved measuring the growth rate of grass under different light conditions.
Tension – The force exerted by a string, rope, or cable when it is pulled tight by forces acting from opposite ends. – The tension in the rope increased as more weight was added to the hanging object.
Design – The process of planning and creating something with a specific function or intention. – The students were tasked with the design of a simple machine that could lift a small weight.
Experiment – A scientific procedure undertaken to test a hypothesis or demonstrate a known fact. – In the experiment, we tested how different materials affected the speed of a rolling ball.
Engineering – The application of scientific and mathematical principles to design and build machines, structures, and other items. – Engineering involves solving practical problems, like designing a bridge that can withstand heavy traffic.
