Its a trick question. The question implies the possibility that the conveyor can keep up with the actual speed of the plane itself and the plane will not get momentum. Regardless if the conveyor is matching the speed of the wheels(which is possible) or the actual speed of the plane(which it can't), the plane is taking off.
Its pretty simple guys. The force applied to plane is at the engine and not the wheels. So regardless of the conveyor belt speed the plane is moving forward which which will cause lift. If for some reason the force was at the wheels through a transmission of some sort, as soon the plane took off, it would crash since the force is causing the wheels to spin not move the plane foward.
Good lord, why are you guys still discussing this? Of course the plane will go forward. Its thrust has nothing to do with the ground. All the conveyor belt means is that the wheels will turn that much faster than they would on normal ground. The plane will go forward at the same speed. Geez....
I'm not sure you understand how friction works. I think you are really thinking of momentum. Wheels don't overcome friction, or at least they are not suppose to. Wheels are designed to have a high static friction so every vehicle maintains solid friction between the wheels and the ground. It's friction that allows cars to go forward. When you "overcome" friction, that's when cars start skidding Also, the problem does not imply that the belt starts moving before the plane so there is no backswards movement established before the engines turn on. You are also making a HUGE error in confusing force with speed. The belt matches speed with the plane, not force. For the speed of the belt to correlate with the lateral force it puts on a plane, the wheels would have to be locked into place so the belt was actually pushing the plane back. In that situation, the plane would go nowhere. That of course is not the case. Your final conclusion that more thrust would be needed is also incorrect. It could keep the normal thrust but it would just take it a little bit longer to get to the ideal speed (assuming it starts out moving backwards). As soon as the engines start, the plane would begin decelerate until eventually it would stop and move forward. The wheels don't matter. Do they have an affect? Sure but it's affect is negligible considering you are pitting them against jet engines that can propel a vehicle over 200 mph. So much so that they would not be worth calculating if you were to document the situation.
This discussion is still going because you guys still do not understand. The guys who are still saying wheels do not matter, belt does not matter, thrust has nothing to do with the ground are wrong. Of course we know the wheels do not move the plane, the thrust moves the plane but don't you get it: 1) The wheels stop the plane from moving because of friction. Let me show you a picture, maybe it will help: The entire article http://webphysics.davidson.edu/faculty/dmb/PY430/Friction/rolling.html That surface moves backward and you have to push the wheel forward. I read that to overcome the friction on a car' tires, it requires about 10HP to keep it moving at 50 mph. My guess is that it needs ~1000 HP for a plane to move 200 mph because of rolling friction alone. Besides friction, you need to move the air, the faster the belt moves back, the more air rushes pass the plane. There is much more work require to move that air so the plane can move forward. If you discount those factors , why do you think a plane needs its engine?
Speaking of moving the air. Have you ever walked into a strong wind before and see how much work is required just to move you own body? Imagine moving your body into 200 mph wind. Then imagine moving an airplane body into 200 mph wind. That is how much work is required just to keep the plane in place if the belt is moving back at 200mph.
I just wanted to tell you both good luck. We're all counting on you. I hope no one else posted this. I'm too lazy to read the thread.
fair=1/2DApv^2 (eq-1) ftire=Crr*N (eq-2) fair = frictional force air D=drag coefficient A=cross sectional area of moving object v= velocity of plane ftire= frictional force of tire Crr=coefficient of rolling resistance (approximately constant, but decreases with increasing speed) N=normal force P=power required to overcome friction P=fair(v)+ftire(v) under normal circumstances. (eq-3) Since the conveyor belt is moving at v speed, let's double the rolling resistance to match that the ground is moving at twice velocity that it should) P=fair(v)+ftire(2v)= 1/2DApv^3+2*Crr*N*v (eq-4) At approximately 50 miles per hour for a car, 86 % (or 76% if you double rolling resistance) of friction is from the air and not the tires. As one can see form eq-4, the higher the velocity, the less the rolling resistance will matter. Therefore, the plane flys
This stuff is very good. Then you come up with this stinker of a conclusion! It's true that more power is required to overcome air resistance than friction on the wheels but you do have to overcome more air resistance to move forward because the belt is moving the plane back! If the belt always speeds up to match the forward speed of the plane, 200mph, 1000 mph .... then the plane has to have more and more thrust ... It's not realistic. There is no such belt, but that is what the original problem stated!!
The belt is not moving the plane back!!!! The belt can never move the plane back because the belt can only go the speed the plane is moving forward. The belt is only making the tires move twice as fast and creating twice as much resistance. Air resistance is only dependent on velocity of the plane and is completely unaffected by the fact that the plane is accelerating more slowly to overcome the additional rolling friction. For an exercise at home: 1) go to walmart. 2) In toy aisle, grab an unwrapped ball. (if you can't find a ball, an unwrapped tonka truck will work) 3) go to checkout line with conveyor belt and place ball on end of belt farthest from cashier. 4) When conveyor belt moves the ball a foot, try to push the ball with one hand at the approximate speed the conveyor belt is moving the other way. (you will notice that at no point will the ball ever move back provided you constantly push the ball the other way). If you are strong enough to push the ball back to it's original position on the belt, jet engines will be able to move the plane a foot. If the plane can move a foot with the conveyor belt moving 1 mph the other way, it has proven it has enough power to overcome rolling friction and it is only a matter of having a long enough runway to compensate for the slower acceleration.
rage, do you even know how a jet engine works against a spinning wheel with lubricated ball bearings? what do you think has more force?
Ok, I did a little more research and found that the key is whether a moving belt could move an airplane. I still maintain that it could. The friction on the wheels does that. You can do the test at Walmart. Put a toy truck on the moving belt and it will move. The part that I was mistaken was not realizing that friction has its upper limit. Moving the belt faster does not move the plane back the same amount. The wheels will start to slip and the belt can only move a plane back up to a certain speed. I stand corrected. Having said that, some of the statements that you guys made are still wrong.
Correct. The answer has two parts. The plane will eventually overcome the friction of the conveyor belt and move forward no matter how fast the belt moves. Once it has a forward velocity it will eventually fly. However... The velocity of the plane is zero while it is on the conveyor belt. So, on a windless day the air resistance and the airspeed of the plane is zero. A plane requires an airspeed > 0 to fly, so the plane will not fly while its on the conveyor belt.
Will be on tonight (Wednesday). Jamie and Adam take wing to test if a person with no flight training can safely land an airplane and if a plane can take off from a conveyor belt speeding in the opposite direction. Tory, Grant, and Kari jump on some Hollywood-inspired skydiving myths.
this question is dumb. if there is a conveyer belt on the runway, why not make the plane take off in the same direction as how the belt is moving, sort of like the catapult mechanism they use on aircraft carriers. anyway, how'd the mythbusters experiment turn out?
