86 Mr Skinner, Note on the Slipperiness of Ice. 



Note on the Slipperiness of Ice. By S. Skinner, M.A., 

 Christ's College. 



[Bead 16 February 1903.] 



Papers on this subject have been published by J. Joly (Proc. 

 Roy. Dublin Soc. v. p. 453, 1886, and Nature, March 23, 1899) 

 and by O. Reynolds (Mem. and Proc. of the Lit. and Phil. Soc. of 

 Manchester, No. 5, vol. xliii. 1899). Both authors attribute the 

 slipperiness of ice to the presence of a layer of lubricating water 

 under the body pressing on the ice. The water is produced 

 by the lowering of the freezing point where the pressure is ex- 

 perienced. On this view the object glides on a liquid layer and 

 consequently viscous friction in water takes the place of the 

 rubbing friction between the solids. Joly shews by calculation 

 that the weight of a man concentrated on the blade of a skate is 

 sufficient to lower the freezing point very considerably, and Reynolds 

 arguing from the difficulty of slipping on very cold ice comes to 

 the same conclusion. In this note I wish to point out that sliding 

 on a liquid layer is a condition under which cavitation will occur 

 in the liquid, and that this will aid the slipping. 



A paper read last term (Proc. Camb. Phil. Soc. xn. 34) was 

 illustrated by an experiment in which a lens, resting on a flat 

 plane with glycerine between the lens and plane, was made to 

 slide, and behind the point of nearest approach a vacuous cavity 

 was seen to form during motion and to disappear as soon as the 

 motion ceased. I find that a similar cavity can be seen when 

 a lens is pressed strongly on ice and pushed along. A cavity of 

 this kind may be formed behind the sliding contact of a hog-back 

 skate, and behind that of a curling-stone. 



It was explained in my paper how the cavity facilitates 

 slipping, for if it is not formed the tensions produced behind the 

 point of nearest approach by the motion of the body over the 

 liquid layer resist the forward motion. 



