All right, welcome to stupid physics tricks. Remember, this is only a demonstration. It's not on the examination. So please, no studying this material. This week, we have Tahir. So come on in, Tahir. You're a student here, right? >> Yep. >> All right, and you took physics freshman year? >> Yeah, I took 101 and 102. >> 101, 102, and now what are you doing? >> Now I'm studying bioengineering. >> Really, bioengineering? >> Yeah- >> So my- >> Physics was that bad. >> My former students are bioengineers now? >> Yeah. >> Okay, could you turn me into the $6 million man? >> I could, we have the technology. >> Really, everything? >> Yeah, faster, stronger, better. >> I need a lot of work. >> We got you. >> What are we doing, what is today's stupid physics trick? >> We're going to have an elastic collision, you and me. >> You and I? >> It's going to happen. >> An elastic, [LAUGH] okay. Well usually when people collide, it's inelastic. Usually- >> Yeah. >> It absorbs energy that our body is designed to- >> I came prepared, we got this. We have a little beach ball right here- >> Okay. >> And you're going to hold on to it. You're going to stand still, and I'm going to come running. >> Okay, okay, and that's going to make it elastic because we, okay- >> Yeah. >> because we have the stalemate, so. >> because I'm going to, I'm going to be going. >> You're going to be going, and I'm going to, now okay, how are we going to know it's elastic? >> So I'm going to be going at you, and then as soon as I hit you, I'm going to stop, and you're going to start rolling. >> Okay. >> So we're going to have some conservation of momentum going on. >> Right, because we're about the same mass. Okay, I'm ready. >> Okay. >> So I'm going to hold this here. I'm going to try not to flinch. I'm going to pretend I'm already the $6 million man. Okay, here we go. Hey, not bad, not bad! [SOUND] >> [LAUGH] >> Okay, it's okay, you're all right. All right, happens all the time. So now, let's look at this. And how are we really sure that this was elastic? Let's see, let's- >> So- >> Draw it out. >> So we have two bodies. >> Yeah. >> They have nearly equal mass. >> They have equal mass. >> They have equal mass. >> Wait, what [INAUDIBLE] is this? >> [LAUGH] >> Okay, they have approximately equal mass. Here we go, here we go, there we go. >> All right, so they have equal mass. But when the first body's moving at a velocity, we break the chalk. And it hits the second body with some velocity, v. The first body will stop moving, and the second body will move with that same velocity, v. >> Okay, so we- >> So we have a conservation of momentum. >> Right, right, if you work out all the math, you do find that the same mass results in mass two, or mass when stopping. Which pretty much happened. >> Yeah. >> All right, nice one. I enjoyed the collision- >> [LAUGH] >> Of physics and bioengineering. >> Yeah.