Engineering Education Podcast

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Season 3 · Episode 20

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Engineers Sadhan and Pius continue an ongoing series of discussions on the fundamentals of mechanical engineering. Today they talk about what they remember about statics, forces, acceleration, moments, relativity, stars, and more.

Our opening music is called “Soar,” and our closing music is called “Polar,” both by artist Chris Pop. You can find more music by Chris Pop on SoundCloud. These are used under a Creative Commons Attribution License.

Subscribe and leave episode reviews wherever you get your podcasts. Support Pios Labs with regular donations on Patreon, by purchasing digital teaching materials at the Pios Labs curriculum store, or by buying a copy of the reference book Engineer's Guide to Improv and Art Games by Pius Wong. You'll also be supporting educational tools and projects like Chordinates! or The Calculator Gator. Thanks to our donors and listeners for making the show possible. The K12 Engineering Education Podcast is a production of Pios Labs.


Pius Wong  0:00 

We are continuing our engineering basics discussion by talking about Statics, and not the electrical kind, here on The K12 Engineering Education Podcast.


Pius Wong  0:18 

We're here for another episode of...


Sadhan Sathyaseelan  0:20 

What is it called?


Pius Wong  0:21 

This is called -- Well, this is The K12 Engineering Education Podcast today, but I think that we're calling this Introduction to Engineering, Introduction to Mechanical Engineering, actually.


Sadhan Sathyaseelan  0:31 

Yeah. So the idea is, what we're going to do is, we're going to pick each engineering. It will be its own season. And in each of those engineering, we are going to look further into what are the different topics that this is engineering field covers, and we'll talk a little bit about some of the most interesting concepts in each of those fields. Not technically. It's a casual conversation, how it's used.


Pius Wong  0:56 

Like in real life.


Sadhan Sathyaseelan  0:57 

Yeah, where it's used. Like, what exactly is it about?


Pius Wong  1:01 



Sadhan Sathyaseelan  1:02 

What do they learn about, and why it is the way it is.


Pius Wong  1:04 

Why the everyday person should care about mechanical engineering or electrical engineering or nuclear, whatever we're talking about.


Sadhan Sathyaseelan  1:10 



Pius Wong  1:10 

And it just so happens that in this season, we're focusing on mechanical engineering.


Sadhan Sathyaseelan  1:15 



Pius Wong  1:16 

And we kind of talked about that in the last episode, why. And all the different things that go into it. And there's a lot.


Sadhan Sathyaseelan  1:21 



Pius Wong  1:22 

And so today, we're drilling down on one specific topic.


Sadhan Sathyaseelan  1:27 

Which is Mechanics and more specifically, Statics.


Pius Wong  1:32 



Sadhan Sathyaseelan  1:32 



Pius Wong  1:33 

In fact, that's a class that they -- that we both had to take in undergrad, I think to get our engineering degrees.


Sadhan Sathyaseelan  1:39 

Yeah, it's actually something you learn even in high school physics.


Pius Wong  1:42 

Yeah. I wanted to talk about that. It's like, when I went to college, and then we had to take a whole class on Statics I was thinking in my head, Oh my god. Do I have to take physics all over again?


Sadhan Sathyaseelan  1:51 

Again? Yeah. [laughs]


Pius Wong  1:52 

Yeah, that's exactly what I thought, and I was like, ugh. But, true fact here, that class and the class right after, which is Dynamics, which we'll talk about, Statics and Dynamics together made me think, Oh, I majored in the wrong engineering discipline. I was majoring in Bioengineering, and I should have majored in Mechanical Engineering, because I really liked the classes, actually.


Sadhan Sathyaseelan  2:14 

Oh, so you did the wrong major after...


Pius Wong  2:18 

I started as a bioengineer, undergrad.


Sadhan Sathyaseelan  2:22 



Pius Wong  2:23 

And as a bioengineer, as any engineer, you have to take Statics and Dynamics and all these other classes.


Sadhan Sathyaseelan  2:28 



Pius Wong  2:28 

And I learned, Oh, man, I should have just been a mechanical engineer.


Sadhan Sathyaseelan  2:32 

Wait, do Computer Science or Computer Engineering...


Pius Wong  2:35 

You're right. No.


Sadhan Sathyaseelan  2:36 

No? Okay. Not every engineer...


Pius Wong  2:37 

This is why some people say computer scientists are not engineers, because they don't have to take all the same stuff that bioengineers and electrical engineers and everyone else has to take.


Sadhan Sathyaseelan  2:47 

What about electrical engineers? I don't see why this would be useful for electrical engineers, honestly.


Pius Wong  2:51 

Well, I remember -- I don't -- Well, there are some things, like if you're designing chips. I do remember that when I was an undergrad, ever electrical, mechanical, bio, and materials engineer, and chemical engineer, and civil engineer, they all took what they called core classes. And it didn't matter what discipline it was you were in. Tou still had to take Statics. You also had to take Introduction to Circuits, and you had to take Introduction to FORTRAN or something.


Sadhan Sathyaseelan  3:23 

Yeah, yeah, I remember we had to take -- even as mechanical engineers, we had to take electronics, simple stuff like how motors work.


Pius Wong  3:32 

Because we would use it though. That was the argument.


Sadhan Sathyaseelan  3:34 

Yeah. So we don't go as much in detail as an actual electrical engineers. But we do go through simple circuits.


Pius Wong  3:41 



Sadhan Sathyaseelan  3:42 

Yeah, I think that maybe that's how they go through it as well. But this is fundamentally Physics. Statics is fundamentally physics. It's mechanics. It's about what a body is. Like, not a physical body, but any...


Pius Wong  3:57 

[laughs] That's the joke.


Sadhan Sathyaseelan  3:58 

Yeah. That is a joke, right? So any kind of body -- it's like anything that has a mass to it, we consider that as a body. And what are the forces acting on it? Are the forces making the body go through movement, or not movement, stillness? So based on that, that's how we divide it, right?


Pius Wong  4:16 

The study of bodies.


Sadhan Sathyaseelan  4:17 



Pius Wong  4:18 

Of things with mass.


Sadhan Sathyaseelan  4:20 

Yes. Okay. There is another word, though. We are also looking at -- When you look at Statics, we also need rigid bodies. So, yeah, so when we look at Statics we take into account, it's not only about the forces acting on it. The forces acting on it as rigid body.


Pius Wong  4:40 

Rigid, as in, it's not like water.


Sadhan Sathyaseelan  4:43 

Not is it like a piece of rope.


Pius Wong  4:46 



Sadhan Sathyaseelan  4:46 

A piece of rope has a mass.


Pius Wong  4:48 

Not flexible.


Sadhan Sathyaseelan  4:49 

It can have forces. Yeah, it can be flexible. Now, the moment that it's flexible, the field becomes study of materials. So for now, we are only looking at, the body doesn't really bend. It's not flexible. It's rigid.


Pius Wong  5:03 

Hard -- Well, maybe hard bodies.


Sadhan Sathyaseelan  5:05 



Pius Wong  5:06 

Not mine.


Sadhan Sathyaseelan  5:08 



Pius Wong  5:08 

But yes, okay, you're bringing back memories.


Sadhan Sathyaseelan  5:10 

Yes, that's statics. So it has to be rigid bodies.


Pius Wong  5:14 

Yeah. Why Statics? Why is it called Statics?


Sadhan Sathyaseelan  5:20 

So my understanding would be -- See if it makes sense to you, as well, right? So it's about all the rigid bodies that are completely -- It doesn't have an acceleration. So, okay, the body is at rest. That's what it means when it's at static conditions, which just means that there is no there's no movement happening in the body or between parts of the body.


Pius Wong  5:44 

So we can move. It's just not getting any faster or slower, right?


Sadhan Sathyaseelan  5:48 



Pius Wong  5:49 

Like I could move at a constant constant speed in space. And if there's no gravity pulling me in anywhere, there would be no acceleration.


Sadhan Sathyaseelan  6:00 



Pius Wong  6:01 



Sadhan Sathyaseelan  6:01 

Yeah. So it's like a car going at a constant speed.


Pius Wong  6:03 



Sadhan Sathyaseelan  6:04 

So the moment it's going at a constant speed, we can assume that all the other forces acting is typically in equilibrium. So when is the equilibrium? It just means it's all balanced. All the forces are -- For every force, you have an opposite force and it cancels out and becomes zero. So it's either that, or it's not moving at all. There's not even a velocity. But in the realistic scenario, that's not even possible because the Earth is rotating and revolving around the sun, and the sun is revolving around the galaxy. So you're always having something happening.


Pius Wong  6:42 

So we're studying an unrealistic...


Sadhan Sathyaseelan  6:46 

Unrealistic. But we're also talking about only in relation to something else, right? So, I guess fundamentally, the point is, if it doesn't speed up or slow down, it means it's in static condition.


Pius Wong  7:00 

If it's motion is going to continue on with nothing really changing it.


Sadhan Sathyaseelan  7:05 



Pius Wong  7:06 

Okay. I can picture that. I can picture a car going at 30 miles per hour.


Sadhan Sathyaseelan  7:09 

Yeah. So it's like at rest. But you know, doesn't have to be still.


Pius Wong  7:15 

Right. You mentioned the word forces. That's also a physics word. And you said the forces are in equilibrium or they're balanced.


Sadhan Sathyaseelan  7:24 



Pius Wong  7:25 

What is force?


Sadhan Sathyaseelan  7:27 

Oh, wow. [laughs] That's a deep question.


Pius Wong  7:30 

I feel like we're talking about religion. You talk about, Oh, the balance of all the forces on our body, and it reminded me of a yoga discussion that we had the other day, but that's not quite the same thing, right? We're not talking about, like, emotional forces, or spiritual -- Well, maybe spiritual forces, for some people. We're talking about physical forces, like the push and the pull that you feel.


Sadhan Sathyaseelan  7:56 

Yeah. And how much you experience push and pull is proportional to how much force you're experiencing, magnitude of force. So, let's say we place -- Okay, what do we have? Let's say we place the laptop on the table.


Pius Wong  8:11 

Okay, this laptop that we're using to record this podcast is on the table.


Sadhan Sathyaseelan  8:15 

Yes. And a lot of people use a laptop, and they always place it on a table.


Pius Wong  8:19 



Sadhan Sathyaseelan  8:19 

Now we can say that the laptop is right now in a static condition.


Pius Wong  8:24 

Right. It is not moving.


Sadhan Sathyaseelan  8:25 

It's not moving, unless you're trying to move the...


Pius Wong  8:27 

Well, it's not getting faster, slower, we should say. It's not accelerating.


Sadhan Sathyaseelan  8:32 

Yeah, the bodies of these, like, two links. Any laptop will have, like, two rigid bodies that are coming together as a joint.


Pius Wong  8:40 

Like the table is -- Wait, you're saying the laptop, itself, is...


Sadhan Sathyaseelan  8:46 

The laptop has a joint there.


Pius Wong  8:49 

Oh, where the monitor opens and closes?


Sadhan Sathyaseelan  8:52 

Yeah. So we need to consider that you're not trying to move that.


Pius Wong  8:57 

So we're treating the whole laptop as a solid...


Sadhan Sathyaseelan  9:00 

As one, yeah.


Pius Wong  9:01 

...monoblock that never bends.


Sadhan Sathyaseelan  9:02 

An L-shaped block. So it's open. It's there. You're not trying to adjust the screen. So it's already set. So right now there is the weight of the laptop, itself, that's pulling it downwards because of gravity, gravitational force. So if it's pulling it, then there is a force that's acting directly downwards, pushing down.


Pius Wong  9:25 

Yeah, why isn't it crashing through the table here?


Sadhan Sathyaseelan  9:28 

Right. So why do we consider it as in equilibrium? And we also know that the laptop's not going anywhere.


Pius Wong  9:35 



Sadhan Sathyaseelan  9:36 

Because for the exact pull, the same amount of pull it's experiencing, the table is giving the push. So when they cancel out each other, the laptop is at rest.


Pius Wong  9:49 

It's an equilibrium.


Sadhan Sathyaseelan  9:50 

It's an equilibrium.


Pius Wong  9:51 

So I heard you say that, for one force, there was an equal and opposite force reacting to it.


Sadhan Sathyaseelan  9:57 



Pius Wong  9:57 

That sounds like something that everyone has said. That's in pop culture.


Sadhan Sathyaseelan  10:00 

Yeah, it's Newton's Third Law, right?


Pius Wong  10:03 

Yeah. Honestly, I don't remember. We can look that up.


Sadhan Sathyaseelan  10:06 

Okay. It's the Third Law.


Pius Wong  10:08 

Thank you Sadhan, for knowing this.


Sadhan Sathyaseelan  10:10 

Equal and opposite. This is the most famous pop-culture...


Pius Wong  10:12 

Yeah. They say that in cartoons, and they use it as an analogy...


Sadhan Sathyaseelan  10:17 

As a joke, too.


Pius Wong  10:19 



Sadhan Sathyaseelan  10:20 

Yeah, we use a lot of -- This is all classical physics, right? So we use  lot of Newtonian equations.


Pius Wong  10:25 

I gotta just say as an aside, I love how technical words end up becoming more poetry-type words as time goes on.


Sadhan Sathyaseelan  10:31 

That's true.


Pius Wong  10:31 

Like the whole phrase equal and opposite reaction that ended up being used by storytellers and stuff.


Sadhan Sathyaseelan  10:37 

As it's even used as a joke, right?


Pius Wong  10:39 

Yeah, exactly. Or the word force, or the word gravity.


Sadhan Sathyaseelan  10:43 



Pius Wong  10:44 



Sadhan Sathyaseelan  10:44 

Spiritual energy. [laughs]


Pius Wong  10:46 

Right. This is part of the reason why there's confusion when we talk about this today, because people have co-opted technical words to mean more than just the literal thing. Like a force is not just a physical push or pull. Now a force is, Oh, I'm attracted to someone, or Oh, it's pulling me to do something.


Sadhan Sathyaseelan  11:05 

Or may the force be with you.


Pius Wong  11:07 

Yeah, exactly.


Sadhan Sathyaseelan  11:08 

It's in the pop culture.


Pius Wong  11:09 

Right, right. Actually, like, I wonder if someone's quantified the force in Star Wars? Is it a push or a pull? I don't know.


Sadhan Sathyaseelan  11:16 

That's what we're talking about here. We're talking about a more physical nature of force. But actually, that reminds me of another thing.


Pius Wong  11:23 



Sadhan Sathyaseelan  11:23 

Einstein's theory of relativity.


Pius Wong  11:26 



Sadhan Sathyaseelan  11:27 

And that, in pop culture, or you know, everyday use, we kind of assume that, you know -- I think he, himself, gave an example of -- It's more of a joking, jovial example, like, relativity is something like, one hour spent with the person you like, versus one hour spent sitting on a hot stove.


Pius Wong  11:52 

[laughs] That's true. That is ultimate relativity.


Sadhan Sathyaseelan  11:54 

Yeah, that is, essentially -- Yeah, that's the idea of when he says time is relative. But I mean, it's a joke. It's not what the equations use. But that's a little tidbit from what you said.


Pius Wong  12:06 

All right. Okay, so there is more to Statics.


Sadhan Sathyaseelan  12:09 

There's a lot more.


Pius Wong  12:09 

We said that in Statics there's balance of forces or equilibrium. And different physical laws like Newton's Third Law. There are different types of forces, to0. I know that -- You bring back those memories of my classes. There's like, linear forces, things that push in a straight line, like when we talked about our laptop here.


Sadhan Sathyaseelan  12:31 



Pius Wong  12:31 

Gravity's pulling it down. The table's pushing it straight back up. Opposite, linearly aligned directions. But like, not everything has just two forces on it, right?


Sadhan Sathyaseelan  12:43 

Yeah, exactly.


Pius Wong  12:44 

Like imagine now, this table that is in front of us. We don't have three people in the room today. No three-person podcast today, but what if all three of us were pushing on this table, like on all three sides, or maybe four people. You've got one person on each side and we're all pushing on the table.


Sadhan Sathyaseelan  13:06 

It would move in the direction I push because I have the strongest...


Pius Wong  13:08 

Because you're stronger than everyone. Okay, there.


Sadhan Sathyaseelan  13:10 



Pius Wong  13:10 

So that's no longer Static -- well, maybe it's Statics, if you don't accelerate it.


Sadhan Sathyaseelan  13:14 

No, if it's balanced...


Pius Wong  13:16 

If it's perfect -- Oh, you're right, if it's perfectly balanced...


Sadhan Sathyaseelan  13:20 

Okay, but here, I'm gonna use a different example.


Pius Wong  13:22 



Sadhan Sathyaseelan  13:23 

Okay, I'm going to go back to the same example of laptop. So you keep the laptop on the table, and it's at rest, because gravity acting down.


Pius Wong  13:32 



Sadhan Sathyaseelan  13:33 

And the table is pushing it up, and it's cancelling out.


Pius Wong  13:36 

So you have two forces.


Sadhan Sathyaseelan  13:37 

Yeah. But why isn't the table sliding around? There is another thing that's happening there. It's not sliding around anywhere.


Pius Wong  13:44 

Like, because I can tell anyone who's listening right now, I'm reaching over the table and I'm pushing my laptop gently and it's still not moving, because I'm really weak.


Sadhan Sathyaseelan  13:54 

Well, there are also some grips used under. But what are the grips doing?


Pius Wong  13:57 

Like that rubber surface on the bottom?


Sadhan Sathyaseelan  13:59 

Yeah. The four knobs, or maybe multiple.


Pius Wong  14:02 

Yeah, well, I'm pushing it. And it seems like it's gripping onto the table and stopping me from...


Sadhan Sathyaseelan  14:08 

From moving it. So it's continuing to be at rest.


Pius Wong  14:13 

I'm pushing it, and if I push hard enough, it will start to move. But you're saying that right now it's still a static...


Sadhan Sathyaseelan  14:19 



Pius Wong  14:20 



Sadhan Sathyaseelan  14:21 



Pius Wong  14:22 

And here we've got a couple different forces on it. Gravity pulling down. The table is pushing back up on it. Now I am weakly pushing it into the side.


Sadhan Sathyaseelan  14:31 

And nothing is happening. It's not sliding at all.


Pius Wong  14:33 

So I believe it's friction...


Sadhan Sathyaseelan  14:35 

It is.


Pius Wong  14:35 

...pushing back.


Sadhan Sathyaseelan  14:36 



Pius Wong  14:37 

All right.


Sadhan Sathyaseelan  14:37 

It is friction. But there is a limit to what the material can offer, in terms of friction. When the force is higher than that, it will start sliding.


Pius Wong  14:47 

So we need someone who's stronger to push more. Sadhan, you should push it a little bit more and see if we can overcome...


Sadhan Sathyaseelan  14:53 

Oh, we don't want to make any noise on the mic, right?


Pius Wong  14:55 

Okay, yeah. So we'll let it be. It'll stay static.


Sadhan Sathyaseelan  14:58 

Keep it at the imagination level.


Pius Wong  14:59 



Sadhan Sathyaseelan  15:00 

So there's another thing I realized in terms of the laptop example itself. So we did talk about how the two parts -- The screen and the keyboard is connected to the joint. And let's say you move the screen, itself, all the way -- not all the way. Let's say you move it -- Oh, yeah, so when you move it a little bit, it doesn't move much.


Pius Wong  15:23 



Sadhan Sathyaseelan  15:23 

But it's generally easier to change the angle of the screen.


Pius Wong  15:27 

So I'm bending the screen the monitor. It's like 90 degrees open right now.


Sadhan Sathyaseelan  15:33 

Okay, so let's say if you open it further and make it...


Pius Wong  15:37 

Now it's like 120 degrees open.


Sadhan Sathyaseelan  15:40 

Yeah, let's say it's 130. But it's at 130. But it has stopped moving. It's not completely falling down.


Pius Wong  15:52 

Right. When you stop pushing it. It stopped moving, too.


Sadhan Sathyaseelan  15:56 



Pius Wong  15:56 

So we got another static scenario. I can see it right there.


Sadhan Sathyaseelan  15:58 

Yeah. So we can call that, moment, the force that you're applying. Now, okay, so let's look at it this way. So when you use your finger and put it on top of the screen...


Pius Wong  16:13 

Right, where my webcam camera is.


Sadhan Sathyaseelan  16:15 

When you push it, it's a lot easier to push.


Pius Wong  16:18 

Let's see. So I'm pushing on the outside. Oh, yeah. It's almost tipping over my laptop.


Sadhan Sathyaseelan  16:22  

No, I'm going to hold this on the bottom.


Pius Wong  16:25 

So I'm going to pull it back...


Sadhan Sathyaseelan  16:26 

It's a lot easier, right?


Pius Wong  16:28 



Sadhan Sathyaseelan  16:28 

Now let's use -- Let's get half the way on the screen, on the side.


Pius Wong  16:34 

So I'm gonna do something that you shouldn't do and push in the middle of the laptop screen.


Sadhan Sathyaseelan  16:38 

It's harder.


Pius Wong  16:39 

Yeah, let's not do that. [laughs]


Sadhan Sathyaseelan  16:41 

Okay, and go further lower. All the way to the bottom of the screen.


Pius Wong  16:45 

Yeah, that's ridiculous.


Sadhan Sathyaseelan  16:46 

That's a lot harder.


Pius Wong  16:47 



Sadhan Sathyaseelan  16:48 

Okay, so what is happening here, the further away, you move from a joint, it's a lot easier to move it, and we call this entire thing, moments.


Pius Wong  16:58 

So if we're trying to rotate a rigid body around some kind of axis...


Sadhan Sathyaseelan  17:03 

Joint. Yeah.


Pius Wong  17:03 

Some kind of joint, when we apply a force perpendicular to that radius -- I'm using a lot of terms here...


Sadhan Sathyaseelan  17:12 

Yeah, no, it makes sense. You're pushing it away or towards...


Pius Wong  17:17 

Like, when you open a door, you put the handle on the -- like, furthest away from the hinge, because, who's gonna open a door with a handle close to the hinge? You pull perpendicular to the plane of the door, because that's the easiest direction to rotate that door. So it sounds like we have an equilibrium of forces when it comes to a rigid body just moving in a direction, but we also have an equilibrium of moments, an equilibrium of...


Sadhan Sathyaseelan  17:47 



Pius Wong  17:47 

...of a body rotating. Like our laptop -- That laptop screen is no longer rotating. It's in equilibrium, both in rotation, and in linear motion.


Sadhan Sathyaseelan  17:59 

Yep. So all the forces are cancelling out each other. And there is also friction that's acting on the joints. But they're all cancelling out each other. That is, it's not speeding up or slowing down. When the net force, or the total force, when you add all of them together, the opposites cancel, and then it comes to zero.


Pius Wong  18:25 



Sadhan Sathyaseelan  18:26 

So that's pretty much what Statics is.


Pius Wong  18:28 

Studying these forces applied in different directions.


Sadhan Sathyaseelan  18:32 

All these different forces, yeah.


Pius Wong  18:33 

Stopping the rotations, stopping the -- or limiting the rotation, limiting the change in rotation.


Sadhan Sathyaseelan  18:38 



Pius Wong  18:39 

Limiting the change in the velocity, changing the motion.


Sadhan Sathyaseelan  18:42 



Pius Wong  18:43 

Yeah. Sliding, that's right. You know the example they would always give in both our physics and mechanical engineering classes regarding statics were, like, these impossible scenarios of, oh, two people are on a giant ice skating rink. And they're pushing each other. And like, it was always these scenarios that don't really happen in real life, because that's the only way you can study it. In class, you got to come up with an ideal scenario that is so uncommon.


Sadhan Sathyaseelan  19:10 

I have never heard that ice skating example.


Pius Wong  19:13 

Well, where you have a frictionless table.


Sadhan Sathyaseelan  19:16 



Pius Wong  19:17 

And we put a laptop on this frictionless table.


Sadhan Sathyaseelan  19:19 



Pius Wong  19:20 

And if I push on one side, it'll just go, but if you have someone else pushing on the other side, it'll balance out.


Sadhan Sathyaseelan  19:25 

Oh, okay, so in the skating rink, two people are pushing each other... got it, got it.


Pius Wong  19:28 

Just the idea of getting rid of friction, getting rid of any kind of reality. Like, I was just thinking that -- What was I thinking? Well, when you were talking about the previous example, with the moments and everything. In real life, objects have all sorts of moving parts. Like our laptop has got, at least, you know, two rigid bodies connected by a joint, and then our own human bodies are connected, you know, with all these things and soft joints and whatever. And I remember thinking, like, oh, my teachers would always simplify a real life scenario down to something that could be represented with a static situation. Like, my body has all these joints in it, right? And it's soft, and it's squishy. And like, I'm accelerating right now as I move my hands, but like, my physics teacher back then would be saying, Oh, no, I'm just going to represent you with a single coordinate point. And gravity is being applied right on that single point. And then the equal and opposite reaction from my chair is being applied on that single point. And that's all you have to worry about. You don't have to worry about anything else. It just makes me think, oh, engineering is all about simplifying things to unrealistic situations.


Sadhan Sathyaseelan  20:44 

Okay, I wouldn't call it unrealistic. [laughs]


Pius Wong  20:46 

I know. But that's the surprising thing. It may be unrealistic for some people to talk about, but it actually is realistic enough.


Sadhan Sathyaseelan  20:56 

For designing things, yeah.


Pius Wong  20:57 

For designing, for calculations.


Sadhan Sathyaseelan  21:01 

It's like very, very useful. So I guess, when would you need to know about the moments we were talking about? About forces cancelling each other, or we don't want friction happening? We don't want one of our whatever building to, to deform or to bend. So where exactly would something, learning about all of these different forces, learning about all of these loads that can happen? So we were talking about forces here. So we can also say force is equal to load, or instead of, instead of me using my hands to push it, if I throw a ball at it, or if we put a weight to move it, it's still the same thing, the same force, in Newtons, that's happening.


Pius Wong  21:46 



Sadhan Sathyaseelan  21:47 

So the question is, where does it realistically -- where is it applied?


Pius Wong  21:51 

Right. In reality, what do we care about Statics?


Sadhan Sathyaseelan  21:54 

Why do we need to learn about all these laws and details that's seemingly so abstract.


Pius Wong  22:01 

It seems like it, yeah. But you had a point. There's actually lots of places where it comes up.


Sadhan Sathyaseelan  22:07 



Pius Wong  22:07 

And you set a couple of them. Buildings. I mean, they shouldn't move a whole lot.


Sadhan Sathyaseelan  22:12 



Pius Wong  22:12 

They should be static. Otherwise, the building might have some issues. So you might want to do some calculations on the Statics of every beam in your building, make sure that all the forces are balanced on there.


Sadhan Sathyaseelan  22:29 

When you're building, obviously, the, the foundations, where the beams -- or the structure that holds the other parts, like the cement, the mortar, or the wooden floors in place, is actually the steel beams that you install in the first place. Now we can call this a frame, framework for the building. So that's one major application in terms of why we understand bodies at rest and what happens to bodies at rest when the forces are acting on it. It's because of this specific thing. If you want to continue to make them at rest, you to understand all the forces acting on it and how we can oppose these forces acting on them. So it continues being at rest or continues being a net force of zero.


Pius Wong  23:14 

We had an example right at the beginning.


Sadhan Sathyaseelan  23:16 



Pius Wong  23:16 

Whenever you have a moving object that isn't changing in velocity, whenever we drive down the road, and I -- I drive at a great constant velocity all the time on the highway. I'm always...


Sadhan Sathyaseelan  23:27 

Yeah, that's awesome, right?


Pius Wong  23:28 

Yeah, I drive at 70 miles an hour, and there's no deviation from that. And so, if you were studying that scenario, the forces on my car are at rest -- or, sorry, are in equilibrium.


Sadhan Sathyaseelan  23:41 



Pius Wong  23:41 

If I use the phrase correctly, it means that my engine is applying some kind of force so that it goes on the wheels, and the wheels, push my car forward.


Sadhan Sathyaseelan  23:50 

Yeah, I think you can experience it. Like, if you're sitting in the car, you can experience it, like...


Pius Wong  23:55 

When you hit on the gas, accelerating.


Sadhan Sathyaseelan  23:56 

When you hit on the gas, it feels like you're being pushed back.


Pius Wong  23:59 

Yes. It's called an accelerator. Yeah, of course. You're applying acceleration. But when you take your foot off the accelerator, and you don't do anything, you just slowly...


Sadhan Sathyaseelan  24:08 

If it's moving at, say -- Okay, let's start with zero, and you kick the pedal, or the gas. Push the gas, and until it reaches 30, you feel like your body is being pushed back, because it's moving forward, and your body's at rest, so it's trying to push back on you. And when you apply brakes, then you will move forward when this car stopping. So relative to each other, one is at rest, one isn't moving. But then when you are going at a constant speed, and you're in the car, both your body and the car is moving at the same velocity, or moving at the same speed. So you don't really feel any emotion. It's like you're sitting in a room, other than the bumps on the road and turning that you make. If it's a straight road, and you know, just going, you don't feel anything. It's like you might as well be sitting in a completely, you know, flat office place, or you know, sitting in a bedroom, you know. But I think application-wise, a building is definitely one of the best examples.


Pius Wong  25:09 

Because also, the cool thing about the building example is that your forces in that situation, they're not applied to a single point.


Sadhan Sathyaseelan  25:17 



Pius Wong  25:18 

Like, I was talking about how, maybe in the car, we were just talking about how the forces are all applied to our body, alone. Or in this chair, I'm just modeling myself as a single point on this chair. But like with the building, a beam, you have forces across the entire beam, at two ends, and the forces are spread out. So you have to worry about how it rotates, as well. And so it's kind of a cool problem to think about that in a Statics scenario. You've got to think about how all these forces on every single part of the beam cancel out. I think that that's cool. Actually, that was the part of engineering that that made me more interested in mechanical engineering, when I took that class. It was the problem-solving aspect of, Okay, I've got this more complicated object, and I'm pushing and pulling it in different ways. How can you add a certain force just to make it balance out just right, so that it stays put? Or besides buildings and beams, you might think about bridges. It's the same deal.


Sadhan Sathyaseelan  26:20 

Oh, yeah. But just another good example.


Pius Wong  26:22 

Because you apply forces, not just on a single point on a bridge.


Sadhan Sathyaseelan  26:25 



Pius Wong  26:25 

I mean, you have 100 cars on the Golden Gate Bridge in San Francisco at any one time.


Sadhan Sathyaseelan  26:30 



Pius Wong  26:31 

Every single one of those cars is applying, you know, a ton of force at a different point on that bridge. And then you've got the different -- What is it, pillars coming out from the earth in the water?


Sadhan Sathyaseelan  26:41 

And also it's not like all the cars are -- It could be trucks, which are like 10 times as much as a car.


Pius Wong  26:45 

It's not a uniform load. It's a very...


Sadhan Sathyaseelan  26:49 

Distributed, varied loads.


Pius Wong  26:50 

What's the opposite of uniform? Random? I don't know.


Sadhan Sathyaseelan  26:53 



Pius Wong  26:55 



Sadhan Sathyaseelan  26:56 

Nonuniform. That's what we use as a technicality here. But yeah, randomness is an everyday usage. But it's a varying load.


Pius Wong  27:04 

You've got to design this bridge for...


Sadhan Sathyaseelan  27:07 

For a different applications. So trusses, trusses are another thing that's great. So if you look at some of the bridges, if you look at the bottom of the bridges, there will be, like, these triangle shapes.


Pius Wong  27:20 



Sadhan Sathyaseelan  27:22 

Different triangle shapes, upside down, you know, pyramid shapes. So from what we have learned on how different shapes behave in terms of different load conditions, we have found that triangles are the best, especially in the bridge case scenario. They are the ones where you can use minimal material. You don't need to use -- You can think about it, like, okay, what if I use a solid iron for the entire bridge? Right? One, it's incredibly difficult to manufacture and install.


Pius Wong  27:51 

A giant block of iron, is that what you're saying?


Sadhan Sathyaseelan  27:52 



Pius Wong  27:53 

So instead of the Golden Gate Bridge, we would just have a giant cylinder of iron.


Sadhan Sathyaseelan  27:57 

Imagine that. That's going to be terrible design, right? Okay. I'm not sure which one is Golden -- is it a San Francisco bridge?


Pius Wong  28:02 

San Francisco, that red one from Full House? [laughs]


Sadhan Sathyaseelan  28:04 

Oh yeah. I don't watch Full House, but I remember what -- I get what you're talking about. But okay, I think I have the perfect example to understand trusses, or a certain level of framework that comes from understanding Statics, is the cranes.


Pius Wong  28:21 

Construction cranes.


Sadhan Sathyaseelan  28:22 

Construction cranes. If you look at them, you'll see that they have small triangle shapes.


Pius Wong  28:27 

Oh, yeah.


Sadhan Sathyaseelan  28:28 

Imagine the entire thing solid metal.


Pius Wong  28:31 



Sadhan Sathyaseelan  28:31 

Okay, that's...


Pius Wong  28:31 

Hey, that's a good -- That's not going to stay up very long.


Sadhan Sathyaseelan  28:35 

It weighs so much.


Pius Wong  28:37 



Sadhan Sathyaseelan  28:37 

And some of these beams are even hollow. So we are able to do that only because we understand Statics. Only because we understand what shapes -- how forces affect different shapes. So without understanding that we would never come up with a design. So right now, that arm, instead of weighing, like, what? Like 50 tons, it weighs one ton. That's one-fiftieth the weight.


Pius Wong  29:00 

Yeah, and I mean, I don't know if you heard recently when one of those cranes fell down somewhere. Even though it's a lighter weight crane with trusses, it was still heavy enough where it causes lots of damage and, you know, kills people. So you can imagine we are preventing a lot of disasters by making most of our cranes lighter weight out of trusses, and using statics to calculate it.


Sadhan Sathyaseelan  29:22 

And also, if it weighs so much, imagine if it's made of solid iron, steel. How much power do you need to move around?


Pius Wong  29:33 

And money .


Sadhan Sathyaseelan  29:33 

What kind of motor could we...


Pius Wong  29:35 



Sadhan Sathyaseelan  29:35 

So that's where it's useful. So to understand how bodies at rest, how they behave when different forces are acting on it, and how can you continue to keep it in rest, what are the shapes that aid in doing that, is all that we learn. And it's core abstraction in Statics,


Pius Wong  29:55 

Do you think that people who lived 10,000 years ago knew about the calculations in Statics, like the stuff that we learned, like the people who built the Pyramids. The Pyramids are static.


Sadhan Sathyaseelan  30:08 



Pius Wong  30:09 

There's an equilibrium of forces there at the end.


Sadhan Sathyaseelan  30:12 

That's true.


Pius Wong  30:13 

I wonder what they did. Was it just guess and check?


Sadhan Sathyaseelan  30:15 

I don't think they did guessing work. I'm sure they had enough evidence.


Pius Wong  30:18 

Maybe it was an empirical thing. It's not like they calculated it...


Sadhan Sathyaseelan  30:21 



Pius Wong  30:21 

...using equations that we did.


Sadhan Sathyaseelan  30:23 

I'm sure there were some calculations involved. Maybe not a static calculation. But I mean, it has to be mathematical. If you want to build perfect pyramids, with the construction of that, I'm sure they use mathematics, geometry to do that.


Pius Wong  30:40 

Maybe not all the things that we use, but they must have done something.


Sadhan Sathyaseelan  30:43 

Yeah. Engineering started with the wheel, when they first invented the wheel, right? So that's still engineering, or when they first found a way to -- Okay, a wheel is just one big technological advancement. But it is also something as simple as learning to plant trees and grow so they can settle down. That's an agricultural technology. It's engineering. We have Agricultural Engineering.


Pius Wong  31:10 

When there's this systematic study of this natural phenomenon.


Sadhan Sathyaseelan  31:14 

Yeah. How can we how can we make something work so that we don't have as much effort?


Pius Wong  31:19 

It strikes me that, yeah, we're talking about statics, which is the equilibrium of physical forces and moments. But the idea of equilibrium in general is so constant across the different fields of engineering.


Sadhan Sathyaseelan  31:31 

Yeah, true.


Pius Wong  31:31 

We're talking about mechanical right now, but there's this idea of balance in civil engineering, even in bioengineering, my field, there's a class, you know, all about biological equilibrium.


Sadhan Sathyaseelan  31:44 



Pius Wong  31:44 

Like the chemical equilibrium between the cells, the inside of a cell and the outside of a cell. Everything has a certain way of making things stay constant. I think the wording in the bioengineering thing is homeostasis in your body. Like to keep all your chemicals and body temperature and everything constant, you need to have a certain balance of chemicals in you. And I guess in that same sense, for objects to be in equilibrium, you got to have that certain balance of forces.


Sadhan Sathyaseelan  32:19 

Yeah. I think the best example I have to emphasize equilibrium is the sun, itself. Or stars. Any stars that you see right now. There's two forces acting, and obviously I'm generalizing this a lot, but...


Pius Wong  32:36 

So this is forces in the -- not in the push-pull sense.


Sadhan Sathyaseelan  32:40 

Oh, it is in the push-pull sense.


Pius Wong  32:41 

Oh, really? Okay.


Sadhan Sathyaseelan  32:42 

So in the push sense, at the core of a star -- I'm going to talk about suns, and let's just talk about the sun itself. So anything that's, like, the sun is a star, right? So you have -- what is happening inside is huge explosions. And by nature, explosion means moving outside from the center, the force of pushing away from the center. And this is happening because of nuclear fusion of hydrogen atoms coming together to make helium. And it creates huge explosions, like a tons and tons of nuclear -- a lot more, like, explosions happening at the center of the sun, which is pushing away everything outside. But then with the mass of what the sun is, you have the gravity acting towards the center. So when they are in perfect equilibrium, when the gravity is -- it cancels out the explosion, you get a spherical ball hanging in the middle of space.


Pius Wong  33:41 

That's really interesting. I didn't think about it like that. No, because now you have all these forces that are acting from the same direction.


Sadhan Sathyaseelan  33:49 



Pius Wong  33:50 

I was always using the example of me sitting in a chair, where the forces are pointing at me, but now you've got -- It's like a point, the center of the sun and you have all these forces pointing outside.


Sadhan Sathyaseelan  34:01 



Pius Wong  34:02 

In all directions, in the spherical directions, and then forces all pulling inside. Gravity in all directions.


Sadhan Sathyaseelan  34:07 



Pius Wong  34:08 

That's really interesting.


Sadhan Sathyaseelan  34:09 

It is. But if you if you take the balance out a little bit...


Pius Wong  34:14 

You get a supernova.


Sadhan Sathyaseelan  34:15 

You get a supernova, or you get a black hole. [laughs]


Pius Wong  34:19 

So we're in this special zone...


Sadhan Sathyaseelan  34:22 

Of equilibrium where life can sustain.


Pius Wong  34:26 

So equilibrium is not boring, like I was first saying in the beginning.


Sadhan Sathyaseelan  34:31 

Wait, you said that?


Pius Wong  34:31 

Well, I was saying basically that, I used to think that the study of these types of physics problems and these simple statics problems, I used to say like, we're just studying simple cases that don't ever really exist. Like, we're studying a laptop that's not doing anything, that's sitting on a table.


Sadhan Sathyaseelan  34:47 



Pius Wong  34:47 

I'm studying an apple sitting on a chair. That's not exciting. We want to study the apple being thrown against the tree or the car, hitting three other cars and everything moving. Well, what you just told me is is kind of a counterexample. Not everything in statics is boring. Statics makes the sun exist. It lets all life exists that we know. It's something special. My laptop sitting there on the table is special because it lets us do this podcast. It's not crashing to the ground because of gravity. And we have Newton's Third Law to help us ensure that the table is keeping it up. Equilibrium is special. Equilibrium in our biology and homeostasis is special so that we're alive. So I think that's why studying equilibrium and statics is good. So thank you, Sadhan. I have a newfound appreciation for Statics.


Sadhan Sathyaseelan  35:37 

That's awesome .


Pius Wong  35:37 

Not as boring as I used to think.


Sadhan Sathyaseelan  35:39 

For equilibrium, specifically, because that's where the sun comes in -- life comes in the picture. Awesome.


Pius Wong  35:46 

So, what are we going to talk about next?


Sadhan Sathyaseelan  35:49 

So we covered Statics, which is part of Mechanics, which is about bodies at rest. Now the question is what happens to the forces -- what happens to the body when it is accelerating? When it's speeding up or slowing down?


Pius Wong  36:03 

Supernova-ing or black hole-ing?


Sadhan Sathyaseelan  36:05 

Yes. So we have the sun. Now we'll talk about black holes...


Pius Wong  36:08 

That's exciting.


Sadhan Sathyaseelan  36:10 

And where the cells from your body, itself, came from, supernovas.


Pius Wong  36:14 

When my body starts to overheat, and then I die.


Sadhan Sathyaseelan  36:17 

Yeah, the same concept, but we're not going to talk about that.


Pius Wong  36:21 

Yeah, that's really morbid. No, we're not going to talk about that.


Sadhan Sathyaseelan  36:23 

No, I think we should. We'll talk about it, because we spoke about equilibrium and the sun, we will talk about how black holes and all those higher molecules are formed in supernovae. But then, essentially, we're going to talk about Dynamics, which is another major field of Mechanics in Mechanical Engineering.


Pius Wong  36:42 

Where we get acceleration. Acceleration's no longer zero.


Sadhan Sathyaseelan  36:45 

Yup. No longer zero. It's gonna move. There's going to be a lot of interesting things that are going to happen.


Pius Wong  36:53 

This has been another special episode of The K12 Engineering Education Podcast with the mechanical engineers Sadhan Sathyseelan and yours truly, Pius Wong. Thanks for listening everybody. Review the show, share the show and send me suggestions on what's interesting to you in engineering education today. A special thank you to the supporters of the show on Patreon, as always, because your donations make all this possible. To find out more about how you can donate to the show, and let me know that you're listening, go to my Patreon page. That's patreon.com/pioslabs. And that Pios is not spelled like my name. It is with an O. So you can find a link to it from the website k12engineering.net.


Pius Wong  37:38 

Today, our opening music is called "Soar" and our closing music is called "Polar," both by the artist Chrispop. You can find more music by Chrispop on Soundcloud under the username Chrispop99, that's Chris with a C-H, or just check out the show notes for a link.


Pius Wong  37:54 

The K12 Engineering Education Podcast is a production of my independent studio Pios Labs in Austin, Texas, where I work on multiple education and engineering projects like this one. So until next time, thanks for listening.


Pius Wong  38:18 

Couple post-show notes. This may be the final episode of the 2018 season. I've been super busy with teaching and actually doing some web development not just for this podcast site, but in general. But besides all that, I wanted to talk briefly about some topic ideas for future episodes once I get the time to cover them. One of the beautiful things about having a podcast is that you're somewhat of a journalist, and people will tell you things. They'll tell you their opinions about engineering and education and STEM education, stuff like that. And they'll tell you it even though they might not want to be recorded in front of a microphone, on the record. A lot of people, especially a lot of educators, former educators, current educators, are not happy with how they're paid. You can see that in the news with the teacher strikes that have been happening next door to Texas and Oklahoma, there's been a lot of news about that, that happened in Washington state. It's all over the country. Here in my district, public school district of Austin Independent School District, there are proposals to cut funding, close schools in the public school sector. And that's not just happening here in Austin, and Austin is a rich city, by the way, I think. But it's happening all over the country, and teachers are mad about it. So all around, I know that educators are feeling the heat, and that's why they're leaving the profession when they shouldn't be. There are also, like, great signs that educators are going into the industry from other industries, too, that they're going into the field, taking nontraditional routes to get certified. And that's interesting. I think maybe we might see that as a pattern to talk about in the coming years, coming months. And so these are the things on my mind, teacher pay, the state of teaching and how people view teaching, whether in the technical professions or not, and the difficulty it is to hire diverse teachers and keep them there, to hire qualified computer science teachers, for example. So, that's something that hopefully I can tackle, come 2019, among lots of other cool things like toys and educational games and the cool stuff being done at the microbrewery nearby, who has hired a chemical engineer to manage manufacturing of their beer. But these are all the things that I would like to cover, and I can't really do it without the support that I've gotten, and with continued support. So thank you so much for donating that dollar monthly to those of you on Patreon. Happy 2018. And I hope it wasn't too problematic for most of you. I hope you enjoy the good parts of it. And I hope that 2019 serves you very well. To all the teachers listening, good luck, enjoy the winter break, and we'll see you in the spring.