At a height, an object has potential energy. As it slips to the ground the potential energy is mostly converted to the Kinetic energy or his speed increases. A very small part of potential energy is lost to friction( As ice hardly has any friction)

I found this amazing explanation physicsclassroom. I was going to write one up myself but I thought this was so good that I had to share it:

Downhill skiing is a classic illustration of the relationship between work and energy. The skier begins at an elevated position, thus possessing a large quantity of potential energy (i.e., energy of vertical position). If starting from rest, the mechanical... more