Returning the Force

How do you actually return your opponent's force back to him?

When pushing with both hands, it is easier to understand this concept. His force from one side can be redirected back at him from the other. That's because there are two points of contact. Much like a wheel. When you push at one point of a wheel, the force turns the wheel, acting on it and in the end, you get an equal force in the opposite direction on the other edge of the wheel.

But when pushing with only one hand, with only a single point of contact, how does one redirect his opponent's force back at him? Each time I resist, my teacher not only doesn't need to move back to absorb my force, he is able to stop me from gaining ground, and at the same time return my force to me, slowly inching towards me if he so chooses. If he wants, he can let me exert all my strength trying to push him, until my arms get so tired that I cannot push anymore. It is like pushing a wall, yet he is very relaxed and doesn't seem to be resisting at all.

So how do you peng without resisting?