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by SamBam 1213 days ago
> You have to decelerate the jug with exactly the right timing to form a straight line, not accelerate it.

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Edit: The quote above, and my original comment below, are wrong. The article is correct. Accelerating the jug at g will create a straight line.

Corrected acceleration model: https://scratch.mit.edu/projects/805927382/

Thank you hannasanarion for the correction.

Indeed, this can be thought of intuitively (though it is slightly counter-intuitive): as the article says, if the jug is moving at a constant speed, the drops will actually make a vertical line under the jug. This is because each drop will be move with the same horizontal speed as the jug.

A decelerating jug, as proposed above, would actually create a backwards line or curve. The drops at the bottom works actually be ahead of the jug.

An accelerating jug is the only way you can get the bottom drops behind the jug.

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My previous comment:

Indeed.

I was pretty sure this was correct, but wanted to model it to confirm. On a Chromebook right now, so Scratch was the easiest way to model and share:

Accelerating jug (cat): https://scratch.mit.edu/projects/805898350/

Decelerating jug: https://scratch.mit.edu/projects/805899100/

1 comments

In your program, each of the balls starts with zero horizontal velocity. This is not analogous to real life, in which the droplets from the jug will have the same horizontal velocity as the jug at the moment they detached. They shouldn't fall straight down, they should follow a ballistic arc. I don't have the skills to set up a simulation of this right now, but I wouldn't be too surprised if the total of those ballistic arcs forms a straight line.
You're totally right. Adding in the ball's horizontal speed makes the article's statement correct: you do have to accelerate the jug by g in order to get a straight line.

Corrected model: https://scratch.mit.edu/projects/805927382/