When you think about it, it's surprising that in-line skating so closely mimics ice skating. Ice skaters glide along with very little friction, while inline wheels grip asphault with "rolling friction." Let's compare the physics of ice skating and in-line skating.
Going forward Coasting Braking Turning Divergence between inline and ice skating
Going forward, ice skaters use the edges of their blades to apply a backward force to the ice, which moves them forward. Inline skaters push against concrete in the same way.
To coast, ice skaters rely upon their "flats" - the flat part of the blade, which slides across the ice instead of gripping into it. During coasting, there is very little friction between the blade and the ice. By contrast, when inline skaters coast, their wheels are rolling, not slipping. Their wheels constantly grip the ground. Therefore, inline skaters reduce the friction that opposes them by buying better bearings, not by greasing the wheels themselves!
Ice skaters use their edges to stop - edges allow a much higher friction contact between the blades and the ice. Ice skaters drag their wheels sideways or use a rubber stopper - they're also creating a higher-friction contact.
To turn a corner, ice skaters use their blade edges to dig into the ice. They push outward on the ice, and the ice pushes them into the turn. If they don't use an edge, they can't turn! Wheel skaters rely on friction between the blades and the street. Wheels spin only forward, not sideways, so it's easy to push sideways. Otherwise, the physics of the turn is identical.
When do inline skating and ice skating diverge? I've been learing all sorts of tricks on ice this semester, but I haven't had time to try them out on concrete. My suspicion is that ice skating moves which rely on the quick transition from edges to flats (low friction to high friction) will be difficult to translate to inline skating. For instance, I predict one can't do a three-turn on blades, since it's a quick edges-going-forward turn-on-flats edges-going-backward kind of move. The mowhawk turn, in which the skater rotates and steps backwards, I predict will be easier on concrete. But again, I haven't tried this yet. I'm planning to find some smooth concrete, slap protective pads on every square inch of my body, and experiment! If you've already tried this, let me know what you've discovered! -jrr
by Karen Knierman and Jane Rigby
