How does a wedge work?
A wedge is two inclined planes placed back to back, with one crucial difference: the wedge moves through the material rather than the material sliding over the plane. A force driven along its length is converted into a much larger force pushing outward at right angles. Ideal mechanical advantage is the length of the wedge divided by its thickness at the back, so a 20 cm splitting wedge 4 cm thick multiplies your blow by five — before friction takes its share.
Why is a thin wedge more effective than a thick one?
Because mechanical advantage is length divided by thickness, so slimming the wedge raises it directly. A long slender wedge splits with far more sideways force for the same blow. The catch is that it must travel much further into the timber to open the same gap, it is more likely to jam, and it is structurally weaker — a thin steel wedge can bend or shatter where a fat one would not. Every axe design is a decision about where to sit on that trade.
What is the difference between a splitting axe and a felling axe?
A felling axe is thin and sharp, made to cut across the grain, so its wedge shape mainly keeps the cut open behind the edge. A splitting axe or maul is deliberately fat, with a short steep taper, because splitting along the grain needs the wood forced apart quickly rather than sliced. The maul has a much lower mechanical advantage and gets away with it, since wood offers little resistance along the grain once a crack has started.
Is a knife a wedge?
Yes — the blade cross-section is a wedge, and the sharpening angle sets its mechanical advantage. A shallow angle around 15 degrees per side gives high advantage and cuts beautifully, but the fine edge rolls or chips easily. A steeper 25 to 30 degrees feels blunter and lasts far longer, which is why a cleaver and a filleting knife are ground so differently. Sharpening is quite literally adjusting a machine's mechanical advantage.
How efficient are wedges in practice?
Poor, by the standards of the other simple machines, because the entire working surface slides against the material under high pressure. Much of your blow is lost to friction and to deforming the material rather than splitting it. This is why a wedge is normally driven with sharp impacts rather than steady pressure — impact delivers energy faster than friction can absorb it — and why a smooth polished face makes a genuine difference to how easily one drives.