Coefficient of Friction

Ice skating was so much fun yesterday. And hey, I only fell twice early in the evening. After last night I have a new found respect for figure skaters and speed skaters. Ice skating is not easy, at all.

One of the interesting links that my chemistry professor gave us was an article about ice. It was interesting in the fact that we are in the year 2006, and we still don't understand why ice is so slippery. It is a solid, and most other solids are next to impossible to skate on. You try to skate down the hallway in your hall and tell me how it goes.

It's intersting because it has a high coefficient of friction yet pressure does not effect it. Let me explain...

The coefficient of friction for a substance describes the amount of force that object exerts as you try to slide something across it. The force of friction acts in a direction opposite to the direction in which the moving object is going. This causes the moving object to accelerate backwards (most people would refer to this as deceleration but that is false. Deceleration is simply an object slowing because of an unequal force acting on it in a direction opposite that of its path of movement) and eventually stop unless another force pushes against the force of friction. In most cases, high coefficients of friction mean that it is harder to slide on object across a surface. And even more interesting, the force of friction is proportional to the normal force. The normal force on Earth is simply the mass of the object multiplied by the force of the earth on the object ( this constant is equal to the acceleration due to gravity, or, roughly, 9.8 N/m).

Now, knowing this, we can assume that the more mass an object is, the harder it will be to slide it across an object with a high coefficient of friction. It's like trying to drag a large refrigerator across the room versus dragging a box of books. However, on ice, you are just as likely to slide on the blade of an ice skate as you are in your car. So why is this?

Some scientist refer to the layer of water just on top of the surface of the ice, but this has been refuted because the water layer is too thin to counteract the force of friction. Earlier than that, scientists believed that the force of the blade on the ice caused enough friction to melt the ice a little leting the blade slide across the surface. This has also been discarded as a false hypothesis because the blade cannot create enough pressure to melt the ice enough to cause the blade to slide so easily.

So why can you slide on ice? Perhaps the bonds between the molecules of water in ice are not completely rigid. Both the negative and positive parts of the water molecule come in contact with the blade. As the blade touches the ice it is both attracted to the positive hydrogen as it is repulsed by the negative oxygen. This constant flux would allow the blade to glide forward without being stopped by the force of friction. A wrong hypothesis I'm sure, and it doesn't explain why cars are just as likely to spin out on ice, but it sounds like a fun idea.