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Saturday, June 18, 2016

Is it possible to create 100% vacuum?

Is it possible to create 100% vacuum?


Is it possible to create 100% vacuum?

Posted: 18 Jun 2016 03:57 AM PDT

Is it at all possible to create 100% vacuum here on earth, if yes. then how?

submitted by /u/rick_dick_ulous
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Can the pressure change of inserting a known quantity of gas into a sealed container be used to calculate the volume of the contents of the container?

Posted: 17 Jun 2016 07:00 PM PDT

So it's really easy to calculate the volume of an object. You just dip it into a filled tub and see how what volume of water comes out. this is called hydrostatic weighing

I'm curious whether a different method could be used. Could a quantity of gas be put into a sealed container of known (empty, tared) volume, and the change in pressure used to calculate how much extra stuff is in the container?

is this practical? How sensitive are pressure meters? how much gas would have to be used? could air be used?

EDIT: while waiting for moderation I found this - https://en.wikipedia.org/wiki/Air_displacement_plethysmography it's actually the application I was thinking of, and lists all the downsides :) Pretty cool that someone has thought of all this and it's amazing to see almost 100 years of work done along some thoughts you just had :) :) What's also interesting is the large effect that the temperature change has, so that I suppose it has to be done quickly. One thing though is that it seems to apply much better to something other than a human subject, since human subjects are warm and damp, changing the conditions during testing (unless it's done quickly). It would seem like an ideal way to quickly measure the volume of a small hard object that you don't want to submerge in water...I'm curious about the generalization of this technique.

submitted by /u/hezwat
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How can any tumor be benign? Isn't all cancer an uncontrolled growth of cells? Why doesn't that fit the definition of all tumors?

Posted: 17 Jun 2016 04:18 PM PDT

Does the density of a material have any relation with its thermal conductivity?

Posted: 18 Jun 2016 07:31 AM PDT

If it does, why?

submitted by /u/Spaffy_Waffle123
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How do parity bits work?

Posted: 17 Jun 2016 11:49 PM PDT

I mean in a Raid array. I know it's a way of being able to rebuild an array by figuring out what the data was. But like how does that work? It's kinda like an Uber form of compression given in an 8tb array: they'll be 6tb of usable space and 2tb for parity space.

submitted by /u/piexil
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Can we calculate how long it would take an object, moving in space, to stop on its own?

Posted: 17 Jun 2016 09:27 AM PDT

I learned today that space is not a complete void, and in fact, creates friction (however minute) for objects moving through it due to gas, dust, etc...

Assuming a spherical object is moving at 100mph in space, and elements such as gravity from nearby objects are not a factor, is it possible to calculate how long an object would need to travel before being slowed to a halt via friction alone?

submitted by /u/NathanielGarro-
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[Gravitation] Why does Newton's law of G apply normally to point masses and uniform spherical masses...?

Posted: 18 Jun 2016 06:21 AM PDT

...but (according to a textbook) if the objects involved are neither point masses nor spherical masses, the formula is still applicable if the objects are placed sufficiently far apart such that their sizes become negligible compared to the distance.

I kind of get it, but how do you explain it in detail? Also, I'd have thought that it is the relative sizes of the objects that makes a space shuttle be treated as a point mass due to its relative small size compared to Earth, rather than its distance from it.

Edit: It's hard to phrase the question in its entirety due to the word limit and 'question mark in title' rule.

submitted by /u/STorrible
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Can someone explain bernoulli's principle?

Posted: 17 Jun 2016 08:18 AM PDT

I am supposed to use it for a project but I can only find complex explanations. Not sure if this is the correct subreddit.

submitted by /u/SpikeSpiegelGod
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Where do our stomachs' get the Chlorine to make hydrochloric acid?

Posted: 17 Jun 2016 09:50 AM PDT

Why does a positive multiplied by a negative equal a negative?

Posted: 17 Jun 2016 03:17 PM PDT

Is there some form of proof for this?

submitted by /u/3dpony
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How fast would the earth have to spin for the centrifugal force to keep a 12 m rope streched if bound to the ground?

Posted: 17 Jun 2016 02:26 PM PDT

What's the difference between a granuloma and a cyst?

Posted: 17 Jun 2016 11:11 AM PDT

What are the effects of pineal gland calcification?

Posted: 17 Jun 2016 08:24 AM PDT

Why does the color wheel seem continuous to our eyes?

Posted: 17 Jun 2016 07:54 AM PDT

The actual spectrum of light visible to human eyes is linear, starting at red and ending in violet (from low frequency to high frequency). How, then, are my eyes processing a color wheel, which manages to loop from violet back to red in a seemingly seamless way?

submitted by /u/Milsivich
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Will a 20% chance become a 100% chance after five times in this situational?

Posted: 17 Jun 2016 07:15 AM PDT

Hello, my friend and I have been scratching our heads over this for some time now.

There are five cans on a fence and each round, 1 is knocked off at random. At the start of each round all cans get reset. If this continues for 5 rounds, will the chance for one can to get knocked off be greater than one that has already been knocked off?

I know that in reality, there will always be a 20% chance amongst all of them but is there some sort of law or theory that i'm not considering here?

Thank you in advance!

submitted by /u/Choppedporks01
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Is it possible that we live inside the event horizon of huge black hole, but we just havent realized?

Posted: 17 Jun 2016 11:35 AM PDT

Why is a >0.5 W laser a diffuse reflection hazard when the diffuse reflection's radiance is significantly less than that of a household light bulb?

Posted: 17 Jun 2016 07:35 AM PDT

According to the standard laser class system and safety guidelines, class 4 lasers (above 0.5 W) are a diffuse reflection hazard. I must be missing something, because both the radiance and irradiance of even a 10 W laser's diffuse reflection is no more than that of a standard 60W incandescent (~10 W in the visible range), which also emits uniformly in all directions. What am I missing? A 10 W laser is universally seen as an acute diffuse reflection hazard. Note that I don't think it can have anything to do with the coherent nature of laser light because the coherence is lost in a diffuse reflection.

(Note: I posted this question in /r/lasers yesterday but haven't gotten any responses over there)

submitted by /u/ButWhoIsCounting
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