 Hi everyone. So up until this point, we've primarily been considering only static loading. However, of course, we can also apply loads dynamically to any part and dynamically means moving, right? So rather than just something sitting on a part or a static load being applied to something, we have a changing load being applied. So the first of two topics that we want to talk about when we when we say that loads are dynamic is impact loading. And impact loading is something being dropped onto a rigid body or a hammer being swung and hitting a rigid body. It's loads that are applied very quickly. And that kind of begs the question, well, what do we mean by quickly, right? So generally, we can consider whether or not something is dynamic by comparing it to the period of oscillation for the rigid body. Now, if you've ever talked about anything related to vibrations, maybe in like a dynamics course, you might be familiar with the idea of the period of oscillation, which is to say, and I'm just going to use a generic equation here to pi root m over k. And this is just a basic formulation for the period of vibration. Now, I recognize we're using tau here, which is normally shear stress. In this case, we're using it to mean period of oscillation. M is mass in this equation, and k is the spring constant. So basically how stiff something is. And if we work out this equation, we can we can calculate the period of oscillation, which would be related to, you know, the frequency with which something vibrates. So if I hit something, and it makes a sound, it's that means it's vibrating with that frequency, the frequency of that pitch of that sound. And the looser something is the lower the frequency is going to be the longer the period of oscillation, the stiffer something is it's going to have a higher pitch sound, higher frequency of oscillation, shorter period of oscillation. So then we can compare against this when we say, well, is something statically loaded or dynamically loaded, because if I slowly apply a load, even though it's changing, it's effectively static, right. And generally, we say that it's static loading, if the time it takes us to apply that load is greater than three times that period of oscillation. And we say it's dynamic, clearly dynamic, if the time it takes is less than one half that period of oscillation. So that gives us a sense of the time scales on which we're talking about here. And then, you know, of course, you may realize there's a gap, right, between one half tau and three tau. And that's kind of a gray area, we could say, well, it's it's sort of static, it's sort of dynamic, we might need to, you know, carefully more carefully consider that situation to see what what makes the most sense in that application. The other thing to think about when we talk about dynamic loading is that it's material dependent, right. If I am loading a piece of steel versus a piece of plastic, those considerations for dynamics are very different, right. And that's possibly going to be captured in that stiffness coefficient k, maybe not. But we know that materials behave differently under dynamic loading, right. And this is especially true in plastics. If you've if you've worked with plastics or done a plastics lab, you probably are familiar with the idea that, you know, if we pull on a plastic slowly, we have stress relaxation, right, and it can stretch. However, if we apply that same load quickly, it tends to snap, it behaves more brutally, right. And that's true of metals too, just on a different time scale. Metals will behave more brutally if they're loaded quickly. And they'll behave more duct as a more ductile or exhibit more ductile behavior, if they're loaded more slowly. So all of these things need to be kind of taken into account as we talk about dynamic loading. So that's a really brief introduction to impact loading, and we'll go into more detail in the next video.