2
$\begingroup$

Looking from the window of a passenger plane even at moderate altitude such that one can still recognize individual waves and even something like white foam, and small boats close to the cost line, it already looks like the water is not moving.

To make more clear what i mean, here is an examplein this video at around 10:40. In HD eye resolution it is much more intriguing, but the video shows the idea, that even when the plane is quite low, waves close at the beach appear to be "frozen".

Why is that? and does that effect have a name?

Improve this question
$\endgroup$
7
  • 2
    $\begingroup$ This isn't really a physics question at all. It's about the human perception system---how you deduce information about movement from visual input. When far from land, you have no stationary references against which to judge the motion of the wave crests, so your visual interpretation system punts. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Jun 17, 2015 at 16:03
  • 4
    $\begingroup$ This is a bit of a hobby horse of mine, because few people seem to be aware of just how heavily edited, filled in, patched together, and outright wrong what they "see" really is. Your eyes lie to you more egregiously than any of your other senses. Treat their reports with considered skepticism. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Jun 17, 2015 at 16:05
  • 1
    $\begingroup$ This is only half of the story. From the point of view of the waves your 400 mph plane is moving like a snail in the sky. $\endgroup$
    – Peltio
    Commented Jun 17, 2015 at 16:15
  • $\begingroup$ Is it really only that? for example in youtube.com/watch?v=GUDV7oVm76k at around 10:45, its like the places where the waves are braking are completely frozen. Whereas normaly they "break" then you have to wait a bit, and then the next one breaks. Maybe its an illusion but i like to understand why i and the video camera see it that way? $\endgroup$
    – Sarmes
    Commented Jun 17, 2015 at 16:54
  • $\begingroup$ @Peltio I understand that when things are far away they appear to move more slow. But im surprised that if many things like waves are far away their relative velocities with respect to each other are also small, while when you are close those waves are interfering all the time. $\endgroup$
    – Sarmes
    Commented Jun 17, 2015 at 17:18

3 Answers 3

Reset to default
1
$\begingroup$

I imagine this effect has to do with the fact that velocity is relative. When you're on the shore, you gauge the velocity of the waves with respect to the shore. When you're in a plane, you're likely gauging the velocity with respect to the other wave crests, which are moving at the same velocity and so there is no apparent movement.

Improve this answer
$\endgroup$
3
  • 2
    $\begingroup$ plus the angular velocity of the waves with respect to your eye (the quantity that you actually see), is very small from the large distance. $\endgroup$
    – Sebastian Riese
    Commented Jun 17, 2015 at 15:59
  • $\begingroup$ I thought about the reference frame idea, but i don't think its like all the waves are lined up carefully and don't move with respect of each other. Especially further from the shore i think waves should be interfering all the time. But the effect is visible even if there are some references like little boats or shore lines, like in the video example in my commend to the first commends, the ocean really looks "frozen" even the breaking waves close to the beach. $\endgroup$
    – Sarmes
    Commented Jun 17, 2015 at 17:08
  • $\begingroup$ @Sames, Deep ocean waves often are mostly coherent (i.e., all of the same wavelength, and all originating from the same apparent source). Ocean waves are caused by wind. If the wind is steady over a wide area, it makes coherent waves. Yet, if you were in a helicopter instead of an airplane, and you could linger for long enough over a single wave crest, you would see the crest slowly flatten out and then turn into a trough. That has something to do with the difference between "group velocity" and "phase velocity", but since I am not a physicist, I don't really understand it. $\endgroup$
    – Solomon Slow
    Commented Jun 17, 2015 at 20:20
0
$\begingroup$

Think of it this way: You are way up in the sky and the distance you see as a centimeter could be meters long since you see objects getting smaller as you go farther away. Assuming that an ordinary water wave travels with a velocity of 3 or 4 m/s at a maximum, it is not hard to imagine that you are seeing them as if they are standing on the ocean.

Furthermore you get to observe the phenomena for a really short amount of time, which means that the displacement of waves is really small compared to the distance from the plane to the ocean, hence the standing looking waves. I would also add that if you were on a helicopter above the ocean observing waves for a long time, you would definitely see them spreading out since that is actually what happens.

Improve this answer
$\endgroup$
0
$\begingroup$

In the video you give at 10:40, where the breaking foam looks set, the explanation is that the foam takes ~5 seconds to cover 10 meters, whereas the plane has traveled a kilometer in those 5 seconds and the foam is no longer observable from the window.

waves

The distance and angular resolution from the plane will also play a role in this.

Improve this answer
$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.