Why Can’t You Change Seats on an Empty Airplane?

It’s the last one a day flight and the plane is empty. So you think, maaay maybe just move a few rows over, where there’s a nice window seat with an unobstructed view of the wing.

Not so fast, buster. The flight attendant says there is no going. You must sit in your assigned seat or you will disturb the weight of the plane. Really? Would moving the average person make a difference? Yes, you know where this is going: Answering this question requires a bunch of weird science. So let’s get there!

In the middle of Mass

People often say that the center of an object is the place where all the gravitational force takes place. That’s a good working definition, and you can use it to solve many physics problems, but it’s not really true. In fact, gravity pulls everything parts of a thing, not just one point.

(Quick side note: We’ll look at center of gravity(not in the center of mass, but in a fixed field of gravity like here on Earth, they are the same.)

If you really want to understand among the masses, you have to think about it torque. Looking back at Newton’s second law, it states that a net force changes the motion of an object (F_net = mass × acceleration). So if the net force is zero, the motion of the object will not change. If it is moving at a certain speed, it will continue to do so. If it is at rest, it continues to breathe.

Here’s a little experiment: Place the pencil on a flat table, and then, taking your two index fingers, push from opposite sides, right in the middle. It just sits there, doesn’t it? Because you are using equal and opposite forces, the net force is zero. But what if you push for it like this:

Push the pencilPhoto: Rhett Allain