I don't fully grasp what makes a wheel much easier to move than to push a solid block.
The pressure at the point of contact between a wheel and the ground must be pretty enormous compared to the pressure created by a block of same material and mass as the wheel.
Friction is defined as the product of normal force exerted on the object and the coefficient of friction between the object and ground. So I assume that for two identical objects of infinite masses this parameter does not make any difference.
Given these circumstances, I don't understand the physics behind it. Am I missing some other attributes of a wheel that makes it easier to move?
Best Answer
Pushing a heavy block across the ground is going to be hard because as you say the frictional force between the block and ground is $F = \mu F_N = \mu mg$ and for a heavy block this is going to be a large force:
But suppose you split your block into two parts, and you put a layer of oil in between the two parts like this:
At the contact with the ground the friction $\mu_1$ is large, while at the oil layer between the two blocks the friction $\mu_2$ is very small because oil is a good lubricant. So now when you push the top block it's going to slide forward with very little force needed, while the bottom block is going to stay stationary relative to the ground.
Although it may not be immediately obvious this is exactly what happens with a wheel. The bottom block corresponds to the rim of the wheel and the top block corresponds to the axle. And in between the axle and wheel we have a layer of oil:
The friction between the wheel and the ground $\mu_1$ is high so the point of contact of the wheel with the ground doesn't slide. However the friction between the axle and the wheel $\mu_2$ is very low so the wheel slides easily relative to the axle. That means when we push on the axle the wheel rotates easily around the axle and rolls forward with very little force needed.