Could a long carbon nanotube be broken by hand? Assuming we could get a single nanotube a metre long, would it be possible to break it by hand or would it slice through just about everything including flesh and bone? Could we even grip it, or would we need an anchor at each end?
 A: Here's a quick and dirty approximation based on some values reported in Wikipedia:


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*Wikipedia lists the ultimate tensile strength of a carbon nanotube as 63,000 MPa, but in a footnote proposes a "theoretical limit of 300 GPa" for multi-walled nanotubes.

*Wikipedia also mentions "most single-walled nanotubes (SWNTs) have a diameter of close to 1 nanometer."


Generously assuming the 300 GPa tensile strength limit, a cable of nanotubes 2,000 nanometers wide (containing on the order of a few million individual nanotubes) would most likely snap under the weight of an apple (on Earth):


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*(300 GPa ) * pi * (1000 nm)^2 = 0.9425 N
For comparison, a human hair is roughly 100,000 nanometers wide.
A: Let's assume a nanotube bundle with a breaking strain of about 1N and a circumference of 5 microns ie 5 x 10^-6m. 
It is wrapped around a finger and in contact with the skin for around 0.02m. The area is pressure exerted over that surface is 10 million Newtons per square metre, which is 10 MPa or some 100 times atmospheric pressure.
I think nobody could break it with their hands because it would slice off all their fingers. Unless anyone cares to comment on the resistance of skin and bone to such pressures?
For reference the nanotube is comparable in radius to the edge of a very sharp razor blade. The difference is, the nanotube is "pure edge" with none of the wedge shape characteristics of a knife. When a knife cuts, a lot of the force needed is due to the fact the wedge shape has to push the side of the cut open as the blade goes deeper.
