Fifth-grader Patrick Lee of Deerpath Middle School shows off some dashing fashion and offers this week’s #tuesdayswithbill question: “Do you think hydraulics could help people with knee problems when their knee breaks down?”

Does Bill have an answer? Well, the guy is an engineer by trade… of course he has an answer! Watch the video to learn a little about hydraulic technology, fluid mechanics, and how the rudder of a Boeing 747 can inspire a better brand of prosthetics.

Patrick Lee: Hi. I'm at Patrick Lee from Deerpath Middle School. I'm in fifth grade. And my question is do you think hydraulics could help people with knee problems when their knee breaks down and it could help it go down much softer?

Bill Nye: Patrick, let me start by saying that is a fabulous tie. Way to go man. It looks good. You know, people are skeptical to pink. I like the pink. I like the purple. I think it's good. Good choice. That is a great question; could hydraulics help somebody's knees? There's a great word they use in medicine: a prosthetic, meaning an artificial limb. I got to say yes absolutely. I don't know how familiar you are with hydraulics, but you asked about it, but the idea is hydro is a word for water and hydraulics use fluids, which do not compress very much. Water hardly compresses at all, if you squeeze it hardly anything happens. And the same is true of the oil in the transmission of cars. And the oil that's in the pistons, the shock absorbers of the car and it's very reasonable that this would work. Because what hydraulics do is so fabulous is they provide a tremendous amount of force from a small object, a small actuator. And the other thing they really help with is what's called damping, which used to be called dampening. But the faster you move something the more damping slows it down. It sounds tricky, but it's not. You've done it.

So what happens in a hydraulic actuator, they'll have an opening, which is another I think it's a Greek word an orifice. So when you try to squeeze the oil or the water through that opening, it slows it down. And the faster you try to go the more it slows it down and this has to do with the nature of fluids. And there's a whole study in physics called fluid mechanics, but yes that is a great idea. You're going to be an inventor Patrick. Way to go man. Let me tell you, I used to work at Boeing on the 747 airplane, which is getting to be an old airplane now, but the president still flies around on a 747. It's a Boeing plane like a 757, 767, 737, 787. Anyway, there's two things I worked on a lot; one of them was a rudder and that's the thing that steers the plane this way. And that thing is so powerful. So there's a pump — there's four pumps by the engines and each pump is unbelievably reliable and just they work for years and years because the thing they pump is oil so they're always getting lubricated, they're always slippery inside which keeps things from wearing out.

Anyway, those pumps make 3,000, we used to all do it in English units, pounds per square inch. As they say, if you want to move a house, if you want to move the Washington Monument that far in a 20th of a second, a 747 rudder actuator will do it for you. And so that is a great idea, man. You can get so much force in hydraulics and a knee could be the perfect place for it. Now just notice when you go to do it you're going to need a place for the actuator to push and you're going to need something to pull with. In my day, I'm sure it still is, this is called a wishbone crank because it's kind of like a wishbone. You're going to need a force and you're going to need a lever, something that's not quite in the same axis as the force. You'll figure it out. That is a great idea Patrick. Be an inventor. Change the world. Nicely done. You know what Patrick, I bet you have someone in your life who needs an artificial knee. Help him or her out. Way to go.