He tied feathers together

How can the plane be so light and fly when it's so heavy? He asked his dad.
That's a good question.
I was sure he'd make up an answer for his small child about wind or magic or it just does. Everyone seated around them gave a laugh. How you gonna answer this one, dad?
Good question.  I think you should think about what makes it fly.
I thought it was a good strategy, having been asked questions that required I'd paid attention
or cared
in school.
I think
and I wasn't close enough to hear answer because of the man sitting next to me talking team sport to someone on his phone and the woman across from me talking airport lunch with her husband.
I could hear the boy's younger sister respond
I THINK THE PLANE FLIES
Shh, inside voice,
I THINK THE PLANE
Shh,
i think the plane flies because it goes in the sky.
Me, too.
The man sat on the floor next to his son
who answered him in his inside voice.
The only word of his answer I could hear aside from wings and wind,
the one that stunned me because he knew it.
Momentum.