Question: If there were a thousand seaguls in an airplane while its flying, each weighing two pounds a piece, but they were all flying in the airplane, would the airplane weigh 2000 pounds more?

Tim Stephens answered on 25 Jun 2012:

I think Tom’s getting himself confused here 🙂

The aeroplane weighs the same regardless of whether it’s flying or stopped on the ground, since weight is the downward force that the plane exerts because of gravity. As you may know, weight = mass * (force because of gravity). On average the force because of gravity is about 10 newtons per kilogram, so a 1kg mass exerts 10 newtons of downward force.

Now, when the plane is on the ground, it exerts its weight through the wheels onto the ground. When it’s flying, it exerts its weight through its wings onto the air that its flying through. To put this another way, the wings push the plane up with a force equal to its weight, so it travels along in a straight line to take you on holiday.

So, the seagulls: When they’re sitting on the backs of the seats waiting to pounce on the in-flight food, their weight is transferred through their legs into the body of the plane, and they add to the plane’s total weight in that way. When the birds are flying, they are part of the air within the plane (their weight is bourne by the air inside the plane), and their weight is transferred into the plane through the air and adds to the plane’s total weight. I’m pretty sure that Mythbusters did a TV show on this a while back.

Tim