Dharsh asked an interesting question the other day; When you are walking up an icy hill and your feet are slipping down, why do your feet start to grip when you run? I started to apply the physics I know to this problem but I couldn't explain it. HANG ON. Who says it is better to run?, it's not what I experience. The problem is the phrasing of the question, you will never be able to explain this because it's not true. The friction is not related to the velocity between the surfaces. Eventually you might melt the ice and then start to grip the road but apart from that can't see why running would increase friction. Algodoo agrees of course.