THE FRIENDLY SKIES...
Lt. Sgt. Jackus writes...Okay, here's something I overheard two guys talking about on the El here at school, and had to get off the train before I could hear a full explanation. The general question is something like this: "An airplane is on a giant runway that is actually a conveyor belt. The Belt moves in the opposite direction the plane is facing. It is rigged up to always move the same speed backwards that the wheels of the plane move forward. If the plane tries to take off, will it?" One of the guys on the train said his teacher said it would take off, so I'm inclined to believe it. But this guy didn't seem to buy what the teach was saying. The teacher was trying to convince him the professor was right. But how?
Well Mr. Jackus, I think I understand the question and if so, can explain the answer.
If I understand the premise correctly, the plane is using a conveyor belt for a runway. That belt is moving backward at the same speed the wheels are moving forward. The thought is that the plane would be standing still and of course, if it was standing still, there would be no airflow over the wings to create lift. If we were talking about a car with wings, this would be true. The wheels are pushing against the road (conveyor belt) and the road is moving backward at the same speed the wheels are pushing forward, ergo no forward movement.
On the other hand, the airplane does not drive on it’s wheels, it pushes against the air. So the airplane would move forward no matter how fast the wheels were moving. Whether or not it will fly is a matter of how fast it is moving compared to the air. As soon as the airplane surpasses its stall speed, it would take off.
What would keep the airplane from traveling forward would be the air speed. If it were to fly into a wind that was as fast as its air speed, it would have no forward motion, though it would still take off. Physics doesn’t care whether the wings move into the air or the air moves into the wings. It only matters that the air does move over the wings fast enough to create enough lift to overcome its weight. We run into this every time we fly. If we have a tailwind, we get there faster. If we have a headwind, it’s going to take longer.
posted by Ask Jim... @ 7:24 PM
8 comments
8 Comments:
But what if the conveyor belt is on an aircraft carrier? And, the carrier is in the gulf stream going north? and the Moon is full and the Earth is spinning and moving around the Sun in a spinning galaxy that is in an expanding universe and there is a large steel tower thirty feet ahead of it? What then?
For an indepth discussion on the naive
theories of motion see Michael McKloskey's chapter:
http://punya.educ.msu.edu/PunyaWeb/courses/summer01/pdfs/naivetheories.pdf
The maple tree will explode, of course.
But if the maple tree explodes and there is no one in the woods to hear it, does it still make a sound?
Jim, I have a question:
Will you be my valentine?
Hey there Jim. I notice that there are some other "Ask Jim" websites out there. Also, there are some "Hey Jims," "Jim's Worlds," and even an "Alaska Jim." Maybe you could do a post on some of the more notable, awkward, and hilarious Ask Jim wannabes out there.
Hey Jim, I have a couple of questions for you.
So tell me Jim, I recently heard that the Asian baseball clubs were peeved by the use of cowhide balls in the upcoming World Baseball Classic, because these Asian teams still use horsehide balls and have only a short time now to get used to cowhide. If I remember correctly, MLB switched from horsehide to cowhide in the 1970's. You don't hear as much about this as you do other rule/equipment changes (i.e., the lowering of the mound). What was the effect of this change, if any, and why was it made?
So tell me Jim, would it be possible to construct a personal diet that would result in absolutely no bodily waste of any kind?
Dear Jim,
Where have you been? What's going on here? Did you start another blog somewhere that I don't know about? Life poses so many questions, and lately Jim has not been posting any answers. PLEASE COME BACK JIM!
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