# What difference does a longer skate make?

1. Jul 13, 2008

### invariant99

Hi. I'll start off by saying I have a background in mathematics, but not in physics. If I use the wrong term, I apologize and I hope that you'll correct me.

I am interested in buying new ice skates and I've been noticing that I can often select the length of the blade as an option (e.g. 30 cm vs 32 cm). As I'm skating along, I expect that means there's more transfer of energy occurring through the blade. Does this translate into an increase in my velocity?

Thanks.

2. Jul 13, 2008

### invariant99

FYI, I tried to model the system with my limited mechanics knowledge, but I'm not sure I did it accurately. I imagined a mass m applying a downwards force across a surface of length x (in metres) and (x + 0.02m) for 1 second of time. I just didn't know where to go from there...

3. Jul 13, 2008

### DaveC426913

This is not the full answer:

- shorter blades increase maneuverability at the expense of speed. So, yes longer blades = better speed but less turning.

4. Jul 13, 2008

### invariant99

So, I guess I'm interested in quantifying it. Is it acceptable to consider the system at a point in time? I'm thinking something like instantaneous amount of work done, but maybe that's not right. I figured doing this might allow me to ignore the effect of friction.

5. Jul 14, 2008

### Phrak

At a guess, assumming smooth ice, I think that a blade half as long will sink about twice as fare into the ice--similar to a wheel where higher friction accompanies smaller diameter wheels. Rolling friction can be modeled as a wheel rolling uphill as a function of the length of the footprint of the wheel in deforming under load. In the case of sliding on ice, where a thin layer of ice melts underneath the blade, I should guess that the depth of melt plus the deformation of the ice is proportional to the length of the blade's footprint on the ice which is a little shorter than the blade's overall length. Without any direct knowledge to base this upon, I'd assume that the ratio of friction, 32/30 is inversely proportional to the area of the footprints to first approximation.

6. Jul 15, 2008

### rcgldr

Must be hockey skates. I recall some rule restricting the length to 30cm, maybe just goalies though, and maybe just certain leagues. I'm not sure how much difference there would be in speed, unless the blade is also curved significantly less. Speed skates have very little curve in the blade.