Why does a spray bottle work? • Hacker News Board

Re: Why does a spray bottle work?

#51

Post by donarb » Sat, Jun 09, 2018, 8:07 PM UTC

userbinator wrote: post #23

davidkuhta wrote: post #21

I found his write-up on MBTA bus mirror positioning to be a short but interesting read as well: https://alexanderellis.github.io/blog/posts/mbta-bus/

Many of the buses I've seen in parts of southeast Asia have their side mirrors hanging in the front instead of jutting out the side, probably for a similar reason (and the streets there are much narrower too.)

Another reason that the right side mirror is higher is to prevent hitting passengers as the bus pulls up to a stop. Passengers tend to step up to the curb where the front door opens up as the bus approaches.

Re: Why does a spray bottle work?

#52

Post by richardfeynman » Sat, Jun 09, 2018, 8:15 PM UTC

SimonSword91 wrote: post #18

This is a nice example to show the illusion of explanatory depth [0]. Most people would say they know how a spray bottle works, but fail to describe all relevant details of the implementation, [0] https://www.edge.org/response-detail/27117

Michael Faraday gave a great series of lectures on how candles work that also illustrates the difference between cursory knowledge and explanatory depth. Most people think they know how candles work, but when you dive into the details there are all sorts of interesting things going on.

https://en.wikipedia.org/wiki/The_Chemical_History_of_a_Cand...

(you can also buy the lectures in book form on Amazon.)

Re: Why does a spray bottle work?

#53

Post by markkanof » Sat, Jun 09, 2018, 8:20 PM UTC

gxs wrote: post #47

MichaelApproved wrote: post #41

Earlier quoted context omitted.

Why isn't this in everything? I'd easily pay an extra few cents to have this in spray bottles. It's such a frustrating problem.

Jumping to the conclusion that everything a company does is calculated and delibarate is a mistake I see a lot of people make, but in this case it’s accurate. In a business that operates at a scale of 100s of thousands if not millions of bottles sold annually, cents matter and can make up a significant portion of revenue. With this in mind, there is a huge incentive to get people to buy sooner rather than later and m…

Maybe, but it seems more likely this isn't due to malice but just stupidity/apathy. Maybe most companies just aren't aware of this technology, or they don't want to implement something new because of uncertainty about the potential problems with the new technology. For example, maybe 1 out of a 100 of these bottles gets completely clogged and won't dispense anything at all. That looks bad for the company and maybe even requires a recall. It's easier to just stick with what they are doing and no-one is complaining loudly about the small bit of wasted product.

Re: Why does a spray bottle work?

#54

Post by otras » Sat, Jun 09, 2018, 8:23 PM UTC

fireattack wrote: post #49

davidkuhta wrote: post #21

I found his write-up on MBTA bus mirror positioning to be a short but interesting read as well: https://alexanderellis.github.io/blog/posts/mbta-bus/

From the map I can't tell how the bus can "go through Bennett Alley and continue straight into the bus tunnel". The streets are not aligned, are they?

Good call! You're right that "continue straight" might not be the best wording, as they aren't aligned on the map. In real life, they're also not perfectly aligned, but the entrance area to the tunnel is much wider than appears on the map, meaning they can take a slight right to continue down the tunnel. My bet is I was thinking about roads in terms of Boston roads, where going straight is often more of an abstract concept than a true direction.

Here's a streetview with Bennett Alley on the right and the bus tunnel on the left if you want to get a feel for the turn:

https://www.google.com/maps/@42.3731803,-71.1223078,3a,75y,1...

Unfortunately you can't see through to the tunnel from the other side of Bennett [0], but the good news is you can see the 3 buses in action!

https://www.google.com/maps/@42.3725618,-71.1225705,3a,85.4y...

Re: Why does a spray bottle work?

#55

Post by richie5um » Sat, Jun 09, 2018, 8:26 PM UTC

gxs wrote: post #47

MichaelApproved wrote: post #41

Earlier quoted context omitted.

Why isn't this in everything? I'd easily pay an extra few cents to have this in spray bottles. It's such a frustrating problem.

Jumping to the conclusion that everything a company does is calculated and delibarate is a mistake I see a lot of people make, but in this case it’s accurate. In a business that operates at a scale of 100s of thousands if not millions of bottles sold annually, cents matter and can make up a significant portion of revenue. With this in mind, there is a huge incentive to get people to buy sooner rather than later and m…

Yup.

Business benefit supersedes customer benefit. Always.

Re: Why does a spray bottle work?

#56

Post by barrkel » Sat, Jun 09, 2018, 8:31 PM UTC

alanbernstein wrote: post #32

maym86 wrote: post #25

Earlier quoted context omitted.

That diagram at the top of the Wikipedia article made the concept more clear to me than the whole orginal post. Drawing the valves like that really helps. Edit: grammar

That's funny, I don't know what that diagram is trying to convey.

I suspect it might have something to do with your mechanical aptitude - the mechanism is suggested by the shapes of the parts. The diagram is reminiscent of those tests we did in school to help choose a career.

Re: Why does a spray bottle work?

#57

Post by hexane360 » Sat, Jun 09, 2018, 8:38 PM UTC

jetrink wrote: post #27

TheSoftwareGuy wrote: post #20

One way valves are basically diodes, but for fluids rather than electrons. You can also make logic gates out of just diodes (or one way valves). Imagine writing software for a hydraulic computer!

MONIAC [1] was an analog computer designed in 1949 that used water to model the national economy of the United Kingdom. 1. https://en.wikipedia.org/wiki/MONIAC

This was brilliantly parodied in Terry Pratchett's Making Money.

Re: Why does a spray bottle work?

#58

Post by jcims » Sat, Jun 09, 2018, 8:42 PM UTC

neuralRiot wrote: post #46

mbell wrote: post #42

Earlier quoted context omitted.

I generally found the fluid analogy did more damage than good for a lot of people in EE school. A lot of people think of electricity as electrons zipping around a circuit at the speed of light due (at least in part) to the water analogy. Having to transition from that world to thinking in charge transfer and fields while electrons move around linearly at a snails pace if at all was very difficult for many people. I'd…

The way the analogy was explained to me when i was a student is that the conductor is a hose filled with water, when you open the valve the water comes out instantly at the other end because the "charge" is moving. It was never confusing to me.

I think anyone that has waited for hot water to get to the tap understands this. Pressure (voltage) transmits at the speed of sound (light). The speed of the particles through the medium, on the other hand, depends on many factors.

Re: Why does a spray bottle work?

#59

Post by hexane360 » Sat, Jun 09, 2018, 8:42 PM UTC

neuralRiot wrote: post #46

mbell wrote: post #42

Earlier quoted context omitted.

I generally found the fluid analogy did more damage than good for a lot of people in EE school. A lot of people think of electricity as electrons zipping around a circuit at the speed of light due (at least in part) to the water analogy. Having to transition from that world to thinking in charge transfer and fields while electrons move around linearly at a snails pace if at all was very difficult for many people. I'd…

The way the analogy was explained to me when i was a student is that the conductor is a hose filled with water, when you open the valve the water comes out instantly at the other end because the "charge" is moving. It was never confusing to me.

This is the correct way. In the water analogy, the circuit is a closed system and components are completely filled with water at all times. For example, the capacitor is a filled sphere with a rubber divider. The total amount of charge/water is constant, but you can change how it is divided between the two plates by an applied voltage/pressure.

Re: Why does a spray bottle work?

#60

Post by fjsolwmv » Sat, Jun 09, 2018, 8:45 PM UTC

richardfeynman wrote: post #52

SimonSword91 wrote: post #18

This is a nice example to show the illusion of explanatory depth [0]. Most people would say they know how a spray bottle works, but fail to describe all relevant details of the implementation, [0] https://www.edge.org/response-detail/27117

Michael Faraday gave a great series of lectures on how candles work that also illustrates the difference between cursory knowledge and explanatory depth. Most people think they know how candles work, but when you dive into the details there are all sorts of interesting things going on. https://en.wikipedia.org/wiki/The_Chemical_History_of_a_Cand... (you can also buy the lectures in book form on Amazon.)

Engineer Guy (a fantastic YouTube channel for learning how things work) has an audiovisual curriculum for this book.

http://www.engineerguy.com/faraday/