Hacker News Reader

Comment by dfc | Hacker News Reader

  > Perfect graphene can take ~100 Gigapascals (14 million pounds per square
  > inch) of force before it breaks...imperfect graphene...~4 Megapascals (580
  > pounds per square inch).

Can anyone put these numbers in perspective? I understand that 100 Gigapascals is a lot, AKA more than anything I personally own. What items does the common person interact-with/own that require > 4 megapascals? I have to imagine that my old titanium lacrosse shaft could handle more than 4 megapascals.

CONTEXT ADDENDUM: Graphene hammer handle versus Hickory Handle?

View on HN

Sure. 100 GPa is 14.5e6 psi. The pressure of an adult human standing on the ground is 1-2 psi (depending on weight, foot size). Pretty much all metals begin to yield at or less than 40e3-70e3 psi.

http://www.wolframalpha.com/input/?i=4+megapascals

I love Google unit conversion. Just enter "100 psi to pascals" as a search phrase and you get an answer. Based on this, it's possible to note some typical things converted into Pascals:

Bike tire pressure 100 psi = 690 kPa

Tensile strength of 6061 aluminum (the most common alloy) = 45000 psi = 310 MPa

Whenever people say that they like google's unit conversion I like to mention GNU units. I would be surprised if google does a unit conversion that units can not handle.

After reading the aluminum statistic it seems that graphene is not going to replace my titanium shaft (that replaced the aluminum shaft).

Can GNU units or anything like it accept a string such as "100F to C" and understand what I'd like? If so I'd love to use that instead.

Temperature conversions are a little goofy because they are nonlinear. Google's 100F to C is:

  dfc@ronin:~$ units
  2866 units, 109 prefixes, 79 nonlinear units
  
  You have: tempF(100)
  You want: tempC
          37.777778

The full explanation is here: https://www.gnu.org/software/units/manual/units.html#Tempera...

I followed the like because I thought maybe i've been doimg temperature conversioms wrong all my life. Temperature conversions are so linear. They need to use a more correct term — e.g. simply proportional.

Having to add or substract a constant before or after scaling does not make a relationship non-linear.

This may be getting pedantic, but the relationship is affine not linear - linear would mean k times the original input would yield k times the original output.

It does not convert currencies like Google.

https://www.gnu.org/software/units/manual/units.html#Currenc...

580 pounds per sq. inch seems a lot for household applications. Say a human were to stand on a Graphene TV, it would be ~250 pounds on ~100 sq. inches, i.e. 2.5 psi.

It seems like a lot until you take into account a woman of middling weight wearing high(ish) heels, which (when in good condition) often have a "footprint" of about 1/16 of a square inch (and much less if, as is often the case since the lift material doesn't last very long, the heal has been worn through to the pin).

Reply on news.ycombinator.com