Why is a bicycle more unstable than a tricycle?

A bicycle is more unstable than a tricycle primarily due to its two-wheel design, which creates a smaller base of support and makes it more susceptible to tipping over. This instability is compounded by the need for balance, as the rider must constantly adjust their body position to maintain equilibrium. In contrast, a tricycle has three wheels, providing a wider base and greater stability, allowing it to remain upright without constant balancing efforts.