How does the apparently small amount of material which comprises the spokes provide the required sturdiness to handle the physics of a human on a bike?
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The strength isn’t actually in the spokes. It’s the rim, it has enormous compression strength but only when pretensioned by the spokes.
If you take the rim without its spokes and lean on it, it will collapse pretty easily.
We can put MUCH more tension on a thin steel rod than compression. In tension, the spoke can take a hundred pounds with no perceivable stretch. But if you compress it, a couple of pounds and the middle is bend out and the endpoints are inches closer to another.
So notice how the sides of the bare rim bulge out as you lean on it, a bit before it buckles? What if we tie the two sides through the middle with 2 horizontal spokes? Actually that significantly increases the force required to buckle the rim, but it next starts bending a bit above and below those 2 spokes. So, spokes are light and cheap, let’s cover those, and cover all the rim.
With the rim’s shape held in place by rigid, high tension spokes, the rim’s compression strength is now stronger by orders of magnitude.
So, the rider’s weight is all pushing down on the axle. The force is in tension across the top half of the rim. The sides are held in place to avoid buckling out.
Now the bottom spokes are a bit more complicated. The rider’s weight is borne through tension on the spokes in the top half, then put the entire rim in compression. But the spokes on bottom are pretensioned so much that they don’t go into compression even when fully loaded. If it went into compression, that would be apparent as the spokes would bow outward
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