Hi, I'm Howie and welcome to Project Strang. Lots of questions around the structures in our world, such as who made them, why they made them, and how they made them. And Project Strang is our attempt to find these answers through understanding structural engineering. This episode we're trying to understand stress and strain, but first let's talk about history. Galileo did a lot more than inspire my favorite part of Bohemian rap city. Galileo! Galileo! He was often credited with a first published theory of the strength of beams in bending, but with the discovery of the Codex Madrid in the National Library of Spain in 1967, it was found that Leonardo da Vinci's work had not only preceded Galileo's work by over 100 years, but also unlike Mr. Figaro himself. Correctly identified the stress and strain distribution across the section in bending. Awkward. Did you know that the world's largest unsupported dome was built 2,000 years ago? Built in the first century, the Pantheon took the title for the world's largest dome for 1,300 years. But still holds the title for the largest unsupported dome to this day. The engineering behind the dome predates to Vinci's work about the distribution of stress and strain by about 1,500 years, and remains an architectural feat for the ancient Romans. Anyways, but inspeitively, Leonardo's accurate appreciation of stresses and strains in a beam subject to bending. He did not provide any way of assessing the strength of a beam, knowing its dimensions and the tensile strength of the material it was made of. This problem was addressed by Galileo in 1638, and his well-known dialogues concerning two new sciences. Illustrated with an unstable looking cantilever beam supported by a wall, Galileo assumed that the beam rotated about its base at its point of support, and that there was a uniform tensile stress across the beam section equal to the tensile strength of the material, which is honestly a pretty stellar realization to have. And now I'll pass it off to Peyton with the interview. So, Brad. Dr. Hunt. Oh, what is stress and strain? Stress is when a force is applied over an area, and strain is the deformation that it experiences. But they are related through a constant called Young's modulus. That is determined by the slope of a stress and strain graph. So, hey, what's that blue thing in your pocket? It's a pool noodle. And if you can see these five marks on the front, when I push it in compression, they get closer together. That's the strain. And when I pull it further apart, they get further apart. That's also the strain. Very cool. Can we carry that around? All the time. How do we use stress and strain in our everyday lives? You experience stress every day when you sit on a chair. You stress the legs. When you get in your car and drive across the bridge, the car is stressing the bridge. When you walk in a building, you're stressing the force lab. You experience strain every day too when you feel deflections when you're moving. What's the deflection? A deflection is a downward movement in a force system or a beam from its original state. And then stress and strain affect the swings. While we're swinging on the swing, we're actually stressing the chains. The chains are holding up our body weight. The weight of our body is transferred through the chain up to the top. And even though we don't experience it because it's so small, they are actually straining. So they are deforming underneath of our own body weight. So there's definitely a thing of too much stress and too much strain. You can have too much stress and an element can fail. Or you can have too much strain and an element can deform too much. And what does it have to do with structural engineering? Structural engineers use stress and strain all the time. A lot of our designs are based on limiting the amount of stress that element experiences. Or limiting the amount of strain that an element experiences to limit the deflections that you feel when you walk inside of a building. Why engineering? I picked engineering because in high school, I was good at math and I love science. I love building things with my hands. Just kind of came naturally to be an engineer. Do you ever feel stressed being an engineer? Meeting type deadlines is always stressful. That's about it. How do you cope with stress? Spending time with the family. Getting outside and enjoying the nice weather. Swinging on a swing. Would you do this every day if you could? If you were stressed at work, just come swing on a swing. Yeah, actually, it should. And what's your favorite formula? I guess the most fundamental thing of structural engineering. Sir Isaac Newton's second law of motion. F equals M A. And that's fourth is equal to mass times acceleration. Why did you pick up a doctor? To get my doctor, it took me five years. Are you stressed out this time of years? No, I enjoyed the process. It was... You enjoyed the process? It was very rewarding. Getting to do cutting-edge research. I did computer modeling of Macer, wrote a thesis based on that. How long was the thesis? About 700 and something pages. Are you serious? That's like a book. Yes, yeah. It's like three books. Yes, it's a book. So basically, stress is a measure of the internal force. Experience by a material when subjected to an external load. Stress is when a force is applied to a material. The generated internal resistance within the material. Strain is a measure of the deformation or elongation that occurs in a material when it is subjected to stress. Strain describes how material has changed or deformed from its original pre-stress composition. Do you see your brain feel bigger after this? I know mine does. Thanks for tuning in. Make sure to smash that like and subscribe button on the way out. And as always, enjoy the process.