Fireside Chat 1 - torque and friction

Dan: Hello, this is Fireside Chat number one, the first one. I'm Dan.

And I'm Hannah.

And today we're going to talk about the physics of holding a coffee mug and we're going to talk about why traditional loop style handles all suck.

Hannah: So Dan, why do traditional loop style mug handles all suck?

Dan: Great lead in. I first discovered this problem quite a while ago, and you may know that I've been working on creating a new handle shape.

Hannah: Oh, are you saying that you've been doing some mug handle science to solve this horrible problem?

Dan: You bet. It's a terrible, horrible problem.

Hannah: And perhaps that is one of the purposes of

Yeah, we should make a podcast.

Okay. Okay. Tell, tell us the science. Okay. Why do they suck?

Dan: So we have this regular mug here in front of us. And imagine, how many fingers do you put in, in the handle?

Hannah: This one I'm putting like three, and my pinky's like outside on the bottom of the loop.

Mm hmm. And my thumb's kind of resting on top.

Dan: Mm hmm, gotcha. So if I think about this, I'd say I may have two or three. I think for me it's about, this one's about two fingers in there. So, your index finger is at the top. Mm hmm. And if you just let it hang there, it would pivot, right? Mm hmm. Yeah, it would fall down.

Yeah. So, if I only have my index finger, the mug will just kind of pivot down and spill my coffee. So, what we think about is when we're trying to support the mug is, how do you keep the mug from rotating down?

Hannah: Mm hmm. And the reason you're also trying to keep the mug from rotating down is because, well, because you keep it from rotating down in this scenario by just, like, clenching it and, like, holding it tight.

Mm hmm. And you're saying that, like, It would be cool if there was another way that didn't involve holding it quite so tight.

Dan: Exactly. So, if I think about this, my index finger is the pivot point. Now we can talk about the concept of torque. Are you familiar with torque?

What is torque?

So torque is when you have something pushing in a direction, and it's far away from a pivot point.

Can you say that in a different way? Yeah. So if I take a wrench and I'm turning a bolt. I grab onto the wrench really far away, and it's easy to turn the bolt, and that's torque.

Torque is like force, but applied in a radial direction. So that I can use that force to turn something. So, what I'm contending with when I want to support this mug, is I don't just want to hold it up vertically, because I can do that easily with my hand if I just grab it from the bottom. But I also want to create torque to resist the fact that the mug wants to go down.

So torque is good. So me creating torque with my hand is good. The mug creating torque trying to rotate itself Is bad. Is bad.

Hannah: So it's a battle of the torques.

Dan: It's a battle of the torques. Exactly. And the the queen of Narnia. came by, she may offer you a Torque-ish delight. Okay so Yeah, so you have torque from this mug, and I need to use my hand and my fingers to generate torque to keep it from falling down.

So, you may wonder how does this normally work? So, , what's happening here is I can feel this finger, my index finger pulling, right? It's kind of pulling up. And if you look at your own hand, Mm-Hmm, . Especially if you try to let go of your thumb what does your index finger feel like?

My index finger. Is it pulling or touching?

Hannah: It's a little pulling, like I can feel it pulling here, and then it's really kind of like resting on my pinky, like I'm kind of like

Dan: Yeah, what it looks like to me is that your index is kind of pulling sideways more than anything. It's not pushing up, and your pinky is pushing up.

Hannah: Yeah, it's kind of like crunching, right now I have like crunching resting on my pinky.

Dan: And so, what's happening is Imagine your index finger pulling, and your pinky pushing, and, and that's gonna create torque. And when I think about torque, there's two things that make it really strong. One is a lot of force, so I can have just very strong fingers, lots of grip.

The other one is a far distance. So it's kind of like if I take a wrench and I'm really strong, I can turn a bolt no matter what. But if I'm not very strong and I grab it farther away, I can turn a really big bolt. Yeah. So when I have these two fingers, there's a far distance between them, so I can create a lot of torque.

Hannah: I feel like the distance thing I've experienced. I, I know that because I've like done stuff where you go further out and you apply force and it works. And I'm trying to think of an example in my

life of when I've done that because I know that I have. But I'm trying to think of something that I've done or is there something that you play as a kid where you're doing that thing.

Dan: I guess one of them is a seesaw.

I was thinking of a seesaw.

Like, if we're both sitting at the very end, whoever's heavier it's gonna go towards them. But, if the heaviest person goes closer to the middle, the light person can just push down, and they'll push the heavier person up.

Even though they're, if they're further out on that, on the seesaw. Yep. If you're further out on the seesaw, you can, yeah. Crank.

Hannah: I was thinking about a seesaw, so I'm glad you mentioned that. Mm-Hmm. .

Dan: Okay. Pop tabs are also like that. So like, oh, you can see there's a, a middle, there's a fulcrum. Mm-Hmm.

that's the word for the middle. And if I pull up on this tab, it's like five times farther away than the little edge. So, my fingers are getting a multiplier, so it's pushing five times harder. Yeah. If I push a little bit on here, it'll push five times more to push the cap of the tab.

Hannah: Are we, are we destined to discuss the science behind drinking receptacles?

Dan: I suppose we are. It's destiny. Was it?

No, it's torque.

Is it destiny? No. Or is it torque? Yeah, so these two fingers are far apart. You can maybe also look, what happens if I just use this finger to push?

Hannah: Makes me nervous you're gonna drop the mug.

Dan: Well, yeah. So this, this finger is pulling, this finger is pushing, and I kind of have to push hard, like it kind of digs in, it kind of hurts, because they're really close together.

But if I move this down, it's a lot easier.

Hannah: So what does all of this have to do with Quirky Cup?

Dan: So Quirky Cup is helping you push further away. So you're getting more leverage with a better part of your hand.

Like a seesaw.

Like a seesaw. So you're farther away and stronger. Than a regular mug.

Hannah: And how, what does that have to do with torque, one more time?

Dan: So if you look at the quirky cup handle that I'll grab.

So in the quirky cup handle, I'm pulling with my index finger, kind of like before. But now, when my palm gets involved, you can see I'm pushing really far away. Like the distance between these two is really big. And I want that to create lots of torque.

Hannah: The distance between your index finger and

Dan: Where my palm touches.

Hannah: And the bottom of the handle. Yeah. So you're creating the most distance between your index finger and the bottom of the mug handle, which is different than a traditional mug.

Dan: Yeah, so you have more distance there. And then the other part that's different is I have a different part of my hand that's pushing, which will be another topic for another day.

But this is causing me to have more torque.

Cool. Fascinating.

You know, the other thing that you might notice if you pick up your mug is your fingers want to slip down. That's the other issue. So, we're talking about

Hannah: fingers want to slip down like this? Yep. Is that because of the shape of the mug handle? Because it's like a circle?

Dan: Yeah, pretty much.

Exactly. So, I don't know how we ended up here with so many mugs like that, but so,

Hannah: who invented the mug handle or the mug?

Dan: They, date back thousands of years. I'm curious to learn that because I think ceramics developed independently in multiple continents and it's pretty old.

There's. advancements in ceramics to make them more capable, but like people have been doing ceramics since you take mud and stick it in a hot oven, or take mud and let it dry out in the sun is ceramics.

So I think there's that key equation where it's like my index finger is pulling.

And something that's really low, like my pinky, is pushing. That's the whole thing, keeping this whole mug up. But if this pinky's pushing, you can see how it's not, like normally if I was pushing on this table, I would push from the side.

Because it won't slip. I wouldn't push on this angled surface. Because that would just be foolish. I'd be like, why don't I push on this thing where my hand won't slip, right?

Yeah.

So here I'm pushing on an angled surface. And the lower that I go to create more distance and more torque, the more it's sitting on this angled surface.

So of course it's just going to slide down.

So then, you may be wondering, well, how can we hold them ever?

That is what I was wondering.

And the answer is, we just have to grip it really hard. We have to squeeze it. If I squeeze it really hard, now I have friction. Mm hmm. And so, because I have contact between these, and there's a lot of force on it, While this is pretty smooth, it still has enough friction to get by, and so if I squeeze really hard I can still push it down, the more I squeeze, the more I can resist that.

My hand's starting to hurt.

So yeah, so squeezing it gives you friction and that keeps it from sliding. You may be wondering, isn't that uncomfortable? The answer is yes. We just live with it. And you may also be wondering if my hands are wet or the mug handle is wet, wouldn't that reduce the amount of friction because water reduces the amount of friction?

The answer is yes. So if you ever try to dip your hand in water and then grab a mug. You might notice you have to squeeze it way harder, or it's a lot harder to hold up.

True. Yeah. Cool.