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Current time: 19th January 2017, 10:52

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What's everyone up to right now?
RE: What's everyone up to right now?
(12th January 2017, 05:41)robvalue Wrote: I was in the same room as her Huh

Ah... the old "you're in the same room as me" trigger...
I've seen it happen more times than I care to count.
Helpful counsel: don't be in the same room as her.

If you really must be in the same room, pretend to be an item of furniture or the dog.
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RE: What's everyone up to right now?
(12th January 2017, 05:45)Iroscato Wrote: So this is pretty cool: I got a Facebook message from an editor-in-chief of a small pop culture news site asking if I'd like to become a writer for them. He came across my profile on Quora, where one of my answers has gained about 45,000 views and counting.
It's a non-paying role, but they're hoping to expand and eventually start generating ad revenue, so there might be some coin in it for me down the line.  Either way, it's a nice chance to hone my writing and apply it to something semi-practical Big Grin

That's probably a cool opportunity for a while, just don't let them exploit you in the long term. They may tell you they can't pay you, but odds are they themselves are in it for the money, and exploiting aspiring writers who need to get exposure is an all too common shtick, the PuffHo is doing it all the time.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition

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RE: What's everyone up to right now?
(12th January 2017, 04:28)Alex K Wrote:
(11th January 2017, 17:56)SteelCurtain Wrote: Maybe I worded it poorly. If the shelf were placed on it's side making the surface angle approximately 20° to horizontal. A wooden block is placed at the on the higher end of the surface. What is the largest mass possible so that the block doesn't slide if the coefficient of friction between the block and the shelf is 0.35?

I distinctly remember problems like this in statics. It may have been dynamics, because it involves movement, but I remember using µ in statics, too.

I'll give you the calculation to show you what I mean - so in that case the force driving the block downhill is m*g*Sin(20)=0.342*m*g. We have to compare that to the maximum force of friction which I assume is given by µ * the normal force pressing the mass onto the surface, which is given by m*g*Cos(20), so the max. force of friction is µ*m*g*Cos(20)=0.35*0.94*m*g=0.329*m*g. Both this and the downhill force have a factor of m, so it cancels out, and the block will slide down the incline no matter what the mass because 0.342 > 0.329

Hmm. That makes sense. Maybe the question asked for the minimal angle? I just remember a problem just like that.
"There remain four irreducible objections to religious faith: that it wholly misrepresents the origins of man and the cosmos, that because of this original error it manages to combine the maximum servility with the maximum of solipsism, that it is both the result and the cause of dangerous sexual repression, and that it is ultimately grounded on wish-thinking." ~Christopher Hitchens, god is not Great

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RE: What's everyone up to right now?
(12th January 2017, 06:04)Alex K Wrote:
(12th January 2017, 05:45)Iroscato Wrote: So this is pretty cool: I got a Facebook message from an editor-in-chief of a small pop culture news site asking if I'd like to become a writer for them. He came across my profile on Quora, where one of my answers has gained about 45,000 views and counting.
It's a non-paying role, but they're hoping to expand and eventually start generating ad revenue, so there might be some coin in it for me down the line.  Either way, it's a nice chance to hone my writing and apply it to something semi-practical Big Grin

That's probably a cool opportunity for a while, just don't let them exploit you in the long term. They may tell you they can't pay you, but odds are they themselves are in it for the money, and exploiting aspiring writers who need to get exposure is an all too common shtick, the PuffHo is doing it all the time.

Eh, let them. I write as a hobby, if it means I can one day get paid for it, it's just an added bonus. If they do manage to actually piss me off, my articles will simply become gradually more and more deranged, containing coded messages inferring they are a bunch of thieving arse-bandits.
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If you have any serious concerns, are being harassed, or just need someone to talk to, feel free to contact me via PM
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RE: What's everyone up to right now?
(12th January 2017, 06:59)SteelCurtain Wrote:
(12th January 2017, 04:28)Alex K Wrote: I'll give you the calculation to show you what I mean - so in that case the force driving the block downhill is m*g*Sin(20)=0.342*m*g. We have to compare that to the maximum force of friction which I assume is given by µ * the normal force pressing the mass onto the surface, which is given by m*g*Cos(20), so the max. force of friction is µ*m*g*Cos(20)=0.35*0.94*m*g=0.329*m*g. Both this and the downhill force have a factor of m, so it cancels out, and the block will slide down the incline no matter what the mass because 0.342 > 0.329

Hmm. That makes sense. Maybe the question asked for the minimal angle? I just remember a problem just like that.

Yup, typically you'd ask for the min. angle, as I did on my last exam Smile
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition

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RE: What's everyone up to right now?
(12th January 2017, 08:15)Alex K Wrote:
(12th January 2017, 06:59)SteelCurtain Wrote: Hmm. That makes sense. Maybe the question asked for the minimal angle? I just remember a problem just like that.

Yup, typically you'd ask for the min. angle, as I did on my last exam Smile

Ha!! But what if it's a wheel? or a sphere? Angel
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RE: What's everyone up to right now?
(12th January 2017, 08:55)pocaracas Wrote:
(12th January 2017, 08:15)Alex K Wrote: Yup, typically you'd ask for the min. angle, as I did on my last exam Smile

Ha!! But what if it's a wheel? or a sphere?  Angel

Depende... do you consider rolling friction? If not it'll accelerate down the hill with g*Sin(20) times some factor that depends on the moment of inertia.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition

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RE: What's everyone up to right now?
(12th January 2017, 08:58)Alex K Wrote:
(12th January 2017, 08:55)pocaracas Wrote: Ha!! But what if it's a wheel? or a sphere?  Angel

Depende... do you consider rolling friction ?

Why? Isn't this a static exercise? For which angle does it start rolling down the ramp?
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RE: What's everyone up to right now?
(12th January 2017, 09:00)pocaracas Wrote:
(12th January 2017, 08:58)Alex K Wrote: Depende... do you consider rolling friction ?

Why? Isn't this a static exercise? For which angle does it start rolling down the ramp?

If you don't consider rolling friction, then for all angles other than zero Smile
Ordinary rolling friction won't change that, except is there is a moment you need to set the wheel in motion, but that's not a simple and material dependendlt quantity I think
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition

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RE: What's everyone up to right now?
(12th January 2017, 09:01)Alex K Wrote:
(12th January 2017, 09:00)pocaracas Wrote: Why? Isn't this a static exercise? For which angle does it start rolling down the ramp?

If you don't consider rolling friction, then for all angles other than zero Smile

That's disappointing... Sad
I thought you said it didn't depend on the mass. There's got to be a small enough mass, depending on the material, where your thing resembles a sphere more than a square box.
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