Homework #5               Glaciology, GEOL 4888,  Spring 2022 Humphrey

1. We did a regelation experiment in class.  We used a 24 gauge copper wire.  We loaded a 2.kg weight on each side of the wire, and hung it over a piece of ice that had a diameter of 6cm.  The wire regelated through half the ice diameter in 1.25 hour. In class while doing the experiment I gave you an expression for regelation velocity (be careful of units: the equation gives you speed in m/s in the MKS system of units).  On the basis of your equation:

a) how does the calculated velocity compare to the observed?

b) we also used a Kevlar string under the same conditions. It may have regelated some fraction of a mm in the same time. Is this contrast between the copper speed and the Kevlar speed to be expected (why)?

Couple of hints: to do this correctly you need to take into account the curvature of the wire as it is dragged through the ice, but it turns out that the forces can be fairly well approximated by assuming the copper is a rigid straight bar and horizontal. Therefore the driving stress is just the total weight (force in Newtons) divided by the wire area, assuming it is a horizontal, not curved, wire. Also note that you will need the thermal conductivity of copper (in Joule/(m s C). [don’t forget to multiply the mass by gravity to get the force]

[If you like math problems: it is possible to calculate the shape of the curve of the wire. As far as I know, nobody has ever published this shape!]

2. Just to force you to do a little thinking about your term project. Write 2 or 3 sentences describing what you are thinking about with regards to the term paper. Tell me the subject and some aspect of the subject that is to be your focus.