Sheep shearing is hard, especially the step where you drag sheep around. What type of flooring is easiest to drag sheep on? There’s only one way to find out.
Some scientists asked sheep shearers to drag sheep 400 times across different types of flooring to determine how best to make sheep dragging easier. Lu and Tirth discuss this baaack-breaking study on S01E03 of the Recreational Science podcast (timecode 9:22):
Tirth: So, sheep are heavy, there’s a lot of sheep shearing for wool, and there’s a lot of occupational and safety hazards associated with sheep shearing. That’s the motivation for this study from 2002. It was published by a bunch of people in Australia.
Lu: Australia, sheep shearing, yeah, makes sense. In Texas, we call Australia the land of shorn sheep.
Tirth: Is that right? Hey, what do you think Australians call Texas then?
Lu: The Australia of America.
Tirth: That’s so true though. That’s so perfect. So, as you’ve already pointed out, Australia is the land of shorn sheep. And the authors note quite importantly that there’s some occupational health and safety hazards associated with sheep shearing. Sheep shearers can suffer from low back pain, knee pain, other injuries and things of that sort. The authors actually very helpfully explain the various steps involved in shearing sheep and how these can lead to different injuries.
Lu: Mhm.
Tirth: So the first step obviously is to catch the sheep, then you have to tip the sheep. Well, I don’t know if they’re tipping the sheep 15% or 20%, but they’re tipping the sheep.
Lu: Oh. Yeah. Usually, in Texas, we usually tip the sheep after, but it’s okay, go ahead.
Tirth: Sounds like you have some experience. I want to hear more about this.
Lu: I do. Look, Tirth, Australia might have invented sheep sharing, but in Texas, we perfected it.
Tirth: Okay. Uh-huh. Is that right?
Lu: That’s right.
Tirth: Well, should I hear your experience first before I list the steps they talk about?
Lu: Tirth, have you never partaken in sheep sharing?
Tirth: Of course not.
Lu: What?
Tirth: I admire sheep from a distance. In fact, a lot of times I confuse them for clouds.
Lu: Well, okay. Let me blow your mind real quick. I went to high school in Texas.
Tirth: Uh-huh. I know.
Lu: My high school was largely agrarian. Just outside of Houston…
Tirth: Uh-huh. The famous farm lands of Houston.
Lu: Yeah, no, you’d be surprised. Hey, Houstonians need food. Astronauts need food. So there was a huge barn on campus because we had very big Future Farmers of America program, FFA.
Tirth: I see.
Lu: Big fan of the program. And in lieu of dissecting a frog or whatever in biology class, we got to shear sheep.
Tirth: No. This can’t be true. This is a story from the 2000’s. We’re not talking about the 1950’s, right?
Lu: No, no, no. Please, we still need wool, and this is good experience for high school students.
Tirth: I see.
Lu: So a group of us would tackle a sheep and take out some razors and shear it for biology credit.
Tirth: So ok, what were your steps for sheep shearing?
Lu: It’s the same steps. It’s catching the sheep, tipping the sheep, dragging the sheep, shearing the sheep, and then guiding the sheep away. Same five steps.
Tirth: Wow. That’s literally what they say here.
Lu: This is the international standard for sheep shearing, okay? This is recognized by the International Standards and Units Committee.
Tirth: Is that right?
Lu: You know the place in France…
Tirth: Yeah, they measure the kilogram.
Lu: Where they have a vault with the kilogram inside? That’s the standard kilogram.
Tirth: Yes.
Lu: In Australia, they have an even bigger vault with the five steps of sheep sharing inside.
Tirth: Wow.
Lu: It’s guarded by Swiss guards.
Tirth: What? Wait a minute. Why are the Swiss cards in Australia?
Lu: It’s been blessed by the Pope. It’s a big deal, man.
Tirth: Wow. I’m learning so much. Okay, so you’ve already helpfully listed the steps of sheep shearing. The experimenters are interested in the ergonomics of sheep shearing in order to prevent injuries in sheep shearers.
Lu: So they’ve identified out of the five steps, one single step that’s the most harmful.
Tirth: Yes, the dragging part.
Lu: Which is bad for your back. So they wanted to make the dragging part easier.
Tirth: Yeah, they wanted to figure out if there was a type of surface that’s most efficient for dragging sheep. So they chose eight men and gave them five types of flooring material to drag sheep on: wood battens oriented parallel, wood battens oriented at right angle, plastic battens oriented parallel, plastic battens oriented at right angle, and lastly, just steel mesh.
Lu: Mhm. So these are like five different types of flooring that they drag sheep across to try to reduce the amount of force required.
Tirth: Exactly, and they measure the drag force across each flooring type. In total there were eight shearers, five sheep, five surfaces and they had each person do 50 trials each for a total of 400 trials. This is a very high number of trials.
Lu: These people are very good scientists. Very, very good scientists.
Tirth: Yes, very impressed. What I found interesting is there’s some figures of the sheep being dragged.
Lu: I’ve seen them. You can see the face of the sheep and they look very content.
Tirth: They look very happy. I mean, this one here looks very smug. So anyways, let’s delve into the results.
Lu: Okay. So just to recap, each of the eight shearers dragged five sheep across five different types of flooring two times each.
Tirth: Yes. That’s correct.
Lu: For a total of 50 trials per person, 400 trials overall, across five different flooring types. All right, tell us the results.
Tirth: Well, the lowest drag force was on the wooden surface, parallel to the direction of the sheep dragging.
Lu: Mhm.
Tirth: And maybe not surprisingly, the highest drag was the steel mesh. The other part that I really liked here is because they had very high number of trials, they were able to do pretty robust statistics.
Lu: Yeah, so quick lesson on science here. I really like this study because there are a couple of things you want to watch out for when you’re doing science. The first one is random error, which is just the random variations in measurements. So, you can measure the dragging force required to drag a sheep multiple times and it’s going to differ every time just due to natural variations. And that’s why, for instance in basketball, the same two teams can play several games and the results will be different each game. It’s sort of the same concept, which is why in the NBA finals, you play seven games.
Tirth: A seven game series. Yeah.
Lu: The way to overcome random variation is to increase replication.
Tirth: The number of trials.
Lu: Number of trials and sample size, which they did. So that’s random error. The other type of error is systematic error, which is not random, but it’s more systematic, it’s more a consistent error.
Tirth: Mhm.
Lu: So this would be like if they have the sheep shearers drag sheep across the five different types of flooring in the same order each time. So start with wood and end with metal every time. There could be a systematic error there in that maybe they are more excited to be dragging on the first type of flooring and then they run out of energy by the last type of flooring. This might consistently change the amount of force they measure on the wooden flooring versus the steel mesh, just due to the order they were tested in.
Tirth: Which by the way, they actually accounted for too. They tried to vary the times of the day when they were dragging the sheep so they wouldn’t get tired.
Lu: Yeah, exactly. And the way to combat systematic error is through randomization: you randomize the type of flooring tested first each time.
Tirth: Yeah.
Lu: So they did that. Good study.
Article citation
Harvey et al., 2002. An analysis of the forces required to drag sheep over various surfaces. Applied Ergonomics. https://www.sciencedirect.com/science/article/abs/pii/S0003687002000716?via%3Dihub
Leave a Reply