Experimental Physics Report - Unexpected Results

[Tantalum]

Hi everyone I have a quick question in regards to an experimental report I'm writing for my year 11 Physics class. Basically we have to test different variables that could effect a bungee cord fiber in relation to stress and strain by increasing the weight force on the fiber until it snaps. For the first part of the experiment I tested the effects of increasing the number of fibers.

The problem I face is that when I measured the diameters of the different grouped fibers using a digital caliper the single fiber was 0.13mm, three fibers was 0.26mm and five fibers was 0.25mm. I just want to know if anyone know why this might be the case, as it also happened when I was making different composite fibers. The method I used for making groups of fibers more than one was by clamping one end and spinning them.

Personally I think the fibers may be pressing into each other and causing the diameter to be smaller than expected. I just need someone to confirm this and explain further; or shows me what's really happening.

Thanks in advance,
Max

 

[SteamKing]

What happens if you take several fibers with identical diameters of 0.13 mm and arrange them in different bundles.
For example, three smaller fibers are not going to lay side-by-side, they are going to pack into something which resembles a triangular cross section, like this:

O
OO

If you really want to find out how the strands with different numbers of individual fibers pack, soak a short length of the middle of your rope in some strong glue, like epoxy. When the glue has cured, cut the rope in two and examine the ends with a magnifying glass.

 

[SteamKing]

Page 1 of this attachment shows the cross section of different rope braids:

http://www.bairstow.com/media/pdf/safety/N7806.pdf

 

[Tantalum]

Thank you, this helped allot.