# Homework Help: Skating shoes

1. May 25, 2005

### Sarahchichi

I want to know why we can easily slide on ice when we wear skating shoes. Originally, I guess it is due to the friction between the metal and the ice. But I think it is not the correct answer. Could anyone help me with this problem.

Thanks a lot,
Sarah

2. May 25, 2005

### whozum

Thats pretty much it, the blade makes a really small contact area with the ice, since its also a thin blade it cuts into the ice a little, but I dont know how that helps.

Also, (combed) ice has a very low friction coefficient.

3. May 25, 2005

### Sarahchichi

When I think deeper into the matter, isn't it because of the heat produced by friction that melts the ice? Then the liquid (water) acts as a lubricant to reduce friction.

4. May 25, 2005

### whozum

Well, I would think that if your skate is melting the ice as your skating along you arent encountering liquid ice since you've already passed over it. I'm sure there is a deeper explanation, but I couldn't help you with much more than I've said.

5. May 25, 2005

### brewnog

Hmm, I always thought that the pressure was sufficient to cause melting of the ice, lubricating the skate/ice interface. I've just discovered it's a myth.

Recent studies show ice at the surface is not the same as the structure of the bulk. It has some of the character of water because not all of the hydrogen bonds are satisfied. It appears that this more subtle effect accounts for the low coefficient of friction of icy surfaces.

Last edited: May 25, 2005
6. May 25, 2005

### Yegor

I'm absolutaly not sure, but I have an idea. What is the difference between skating and ordinar shoes? Skating shoes have very thin surface. Why do we need it? May be, because of men's body must be inclined (refering to ice's surface). It's like a bicycle on the arc. When we slide each step we are moving across the arc, aren't we?. Then there appears a net force which is directed to the centre of circle. But if we are moving across the straight line a have no ideas (realy, how we can preserve equilibrium in this way?).
I hope, my english is understandable.

7. May 25, 2005

### Yegor

8. May 25, 2005

### OlderDan

The second article describes an investigation into the nature of the surface of the solid, which for any solid has to be different from the bulk material. You cannot expect the bulk properties, where every mollecule is completely surrounded by like molecules, to be the same as the surface properties. Which raises the question of how can you expect to refute the idea that ice skates melt ice at the surface by doing a simple pressure calculation that applies to the bulk material.

I think both articles make the point that there is something about the surface of ice that is different from the bulk properties that is somehow connected to reducing the friction of ice skates, but neither of these articles refutes the idea that the ice under the blade is melting. Perhaps the conclusion to be drawn from the second article is that it is a lot easier to melt a little bit of ice at the surface by applying pressure to it than one might predict by considering the application of pressure to the bulk material.

The question of whether the ice melts under the skate would best be answered by looking for water in the skate trail immediately after the skate has moved on, or for a change in the surface . Why is it that on fresh ice you can always see a trail of the skate? It is because the ice that was there is not where it used to be, even if the skate is moving perfectly straight. The ice has not been scraped away as it is when the skates move sideways. Where did it go? If you get an ice cube out of your freezer and run a knife over it, the knife leaves a depression, even if the pressure is very small. It leaves a depression because the ice melted under the blade. You can see it and you can feel it. The ice that was there is gone.

The point is, neither of these articles debunks the "myth" that friction is reduced by a layer of slippery water under the skate blade. What may well be true is that you cannot account for that melting based on a simple pressure calculation relating to the bulk properties of ice, but you might very well account for it with a better understanding of the nature of the ice surface.

9. May 25, 2005

### whozum

OlderDan should come with a set of cliffnotes :)

10. May 26, 2005

### Sarahchichi

thank you all and the website