19. Fluid Mechanics
Buoyancy & Buoyant Force
Hey guys. So let's check out this conceptual buoyancy question, and I chose this one because it's pretty tricky and there's quite a few of these kinds of tricky buoyancy questions I wanna help you think through, so let's check it out. So here we have a piece of wood and a piece of metal, and they both have the same volume. So I'm gonna say volume would equals volume metal. They're both place in a large water tank. The wood is going to float. Let me draw the wood over here and the metal sinks to the bottom. And that's what you would expect would almost always floats. And metal almost always sinks. And we want to know what is the greater buoyant force on it. So which one has the greater FB? And before I go, I want you actually think about this for a second, maybe positive video. If you need to and pick one, I want you to select an answer. Commit to it. Don't be scared. Pick one and then keep going to see if you got it right. And what most people do here is they try to think about this logically, which sounds like a good idea. But the problem is these questions exist because they are tricky and because they sort of defy common sense. Right. So what I like to do is I always like to delegates the decision making to the equation. What I mean by that is that instead of me thinking through it logically or using common sense because I know that that fails and I'm ready for that, I'm going to instead write the equation and let the equation this side. So what is the equation for buoyant force? The equation for buoyant force is density of the liquid gravity and the volume of the object that is under the liquid. Okay, now check this out. Both of these guys are underwater, so the density of the liquid is the same because they're in the same liquid. So this is a tie, which means that this is not going to help you determine who Which one has the more more buoyant force? A greater buoyant force. They also both experienced the same the same little G because they're both, you know, the earth there next, each other. Now it's all gonna come down to the volume under and they both have a total volume of 50. But the wood is is, um, has some of its volume staking out. So the volume under, I'm gonna make up some numbers. It's gonna be, like 10 and 40 for example, and this is gonna be all 50 of it are gonna be underwater. So the the metal has mawr. The metal has mawr of its total volume underwater, um, than the wood does. Therefore, the stronger, buoyant force will be meadow. And hopefully you got this right. But a lot of people actually incorrectly pick would because they think it's floating. So it must be if it's floating, it must be that the force pushing it up is stronger. It must be that the force pushing it up is stronger than the other one. That's not why it floats. It floats because the M G is much, much smaller. Okay, so here the forces, actually, let's draw some arrows here. The F B is actually stronger than here, but the M G is much, much stronger than here. Okay, so don't get caught up right the equation and use that to determine the writing. So let's keep going
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