Hacker News Reader

Comment by roywiggins | Hacker News Reader

Our intuitions about macro stuff is really bad, or at least the intuition of people not steeped in Newtonian mechanics is really bad. Gallilean relativity is deeply unintuitive to many physics-naive people, let alone Newtonian mechanics. There's a reason Aristotelian mechanics lasted so long (okay, also the lack of a real scientific method, but still).

To demonstrate, ask a random person these questions:

If I stand on an airplane and jump, do I land where I started, further back, or further forward, relative to the plane?

if I whirl a ball on a string clockwise around my head and let go, does (neglecting vertical motion) the ball travel

A) curving counterclockwise B) curving clockwise C) in a straight line

View on HN

You'd land slightly back because you'd lose contact with your impeller. I also think most everyone understands how a sling and rock work. Not sure I agree withyour premise. Could you shove a camera in people's face and get dumb answers? Sure. Not sure that's endemic.

You begin at rest, relative to the plane. You jump and experience a force vertically. You land. You haven't experienced any forces horizontally, so you land exactly where you started.

Losing contact with the ground has nothing to do with it. You don't need an "impeller" to continue uniform motion- see Newton's first law.

Maybe I don't understand this thought experiment. Say you are on a plane cruising at 500 mph. The plane is applying constant thrust to counteract atmospheric drag in order to maintain steady 500 mph. At this point your horizontal speed is 500 mph and your vertical speed is zero, as the plane is maintaining level flight. When you decide to jump, you start accelerating towards the ground at roughly 9.8 m/s^2. Your horizontal speed is still close to 500 mph, but it starts decreasing due to atmospheric drag. So you are falling towards the earth, but you are also moving at a considerable horizontal speed relative to the ground due to newton's first law. The plane keeps apply thrust to maintain 500 mph. Eventually you'll land, behind the place but a considerable distance away from where you started.

I may have been imprecise: I'm talking about jumping inside the plane, not wingwalking. There's no drag inside the plane.

If you've ever taken a pee standing up on a plane, you'll notice that your pee doesn't veer rearward. You can juggle balls without losing them (you can try this in the back of a car). If you throw a ball forwards on a plane, it doesn't come back to you, and those carts that are rolled up and down the aisles aren't constantly trying to flee towards the back of the plane.

Well yes, standing inside the plane is a very important distinction. If you are standing inside and decide to jump, there is no atmospheric drag inside the plane to slow down your horizontal speed because any atmosphere in the plane is moving at the same speed you are and so the relative speed is zero.

You might want to read Carlo Rovelli's paper https://arxiv.org/abs/1312.4057.

TL;DR Aristotle's physics lasted a long time because it works in the environment in which people used it.

"If I stand on an airplane and jump, do I land where I started, further back, or further forward, relative to the plane?"

I would say, that most people would answer correctly, that you would not land on the same place, but probably be blown away far backwards from air friction (even though they would just call it wind).

I was imprecise: I'm not talking wing-walkers, I mean standing inside a plane, where wind is hopefully nonexistent

Hm ... and then you expect people would say, they would land backwards? I think allmost everybody would get it right ...

This is based on muddled memories of a highschool physics class, but yes- I'd expect a lot of people to get it wrong, based on the sheer number of my classmates who persistently got it wrong. My teacher subscribed to a slightly nuts teaching philosophy which involved polling the class repeatedly, so I had a pretty good sense of how hard people found the ideas.

Example: literally the other reply to my comment. The notion of an "impeller" to continue uniform motion is Aristotelian, and it seems to coincide with a lot of people's intuition:

https://news.ycombinator.com/item?id=14175605

> The notion of an "impeller" to continue uniform motion is Aristotelian, and it seems to coincide with a lot of people's intuition:

It also coincides with the kinds of experiment that people using Aristotelian physics are in a position to perform. See my comment about Carlo Rovelli's paper.

Reply on news.ycombinator.com