Here I am pictured riding an ordinary bike, but with an extra wheel attached to the front axle. The tyre has been removed to give a little clearance from the road and some copper cable (earthing cable with green insulation) wound around the rim in its place to replace the moment of inertia due to the tyre. The "extra" wheel can be spun up by hand, before you start riding, at any speed you like, even several times the speed of spinning of the "actual" wheel. It can be spun either forwards or backwards and what is so clear is that it really makes no difference to the "ride" of the bike. The bike is just as easy to ride whether the extra wheel is spinning or not, forwards or backwards, fast or slow. So this makes us wonder: "How do we stay up on a bicycle"? The way we stay upright on a moving bike is by active control through steering. This is why we have to learn to ride a bike. If, as learners, we find ourselves falling over to the left then we learn to steer the bike to the left, which generates forces that tilt us back upright again, thereby putting the wheels back under our centre of gravity. Beginners are very wobbly, but as we become expert the corrections become smaller and we can ride in a straight line. The faster we ride, the smaller the steering adjustment needs to be, simply because the bike moves much further in a given time. When riding very slowly the steering adjustments required are very large. When completely at rest, active steering can do nothing for us. A good analogy is to ask, "Why is it easier to hop (or pogo-stick) along a straight path than it is to stand still on the ball of one foot?" The reason is that we use each hop to generate correcting forces and also to put our foot down in a new place that is closer to where we need it to be in order to maintain our balance.