The plane and the conveyor belt, pt. 2

February 10th, 2006 | Comments (3) | Trackbacks (0) |

Like I said, I did a bunch of reading about this riddle after I thought about it for a while. My brain ended up hurting pretty badly, but a few key quotes helped me significantly. One of the best (and, ironically, simplest) explainations was by a commentor named Jason on kottke’s post. He says:

The point of the riddle is that the motion of the wheels exerts only a minor frictional force opposing the forward movement of the plane. The major force being supplied is from the plane engine, and that force is a forward force. The net force is equal to the forward force minus the negligible frictional force. This obviously produces a net forward force. Therefore, the plane moves forward, regardless of how much the wheels are spinning. The plane is not remaining stationary on the conveyor belt becasue there is a force acting on the plane that is not dependent on the motion of the conveyor belt.

Another good explaination of why the plane will take off can be found here. An excerpt:

The difference between a car and a grounded airplane is that a car uses its wheels to propel itself forward, and an airplane moves itself forward by moving air. They assume that the runway moving backwards would move the plane backwards. This is what would happen with a car (that is in gear), so why not for an airplane? Well, because an airplane’s wheels are free rolling. There is obviously some friction, so there would be some small backwards force, but it would be infinitely small as compared to the forward thrust of the airplane.

Yet another place explains why the plane will take off, although it would initially seem otherwise:

A thought experiment commonly cited in discussions of this question is to imagine you’re standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you’ll have to overcome some initial friction tugging you backward, in short order you’ll be able to pull yourself forward easily.

So, now do you believe?