KnowHOW team explains: At rest, the bicycle is unstable because it has no base of support. A base of support is the polygon formed by an object?s contact points with the ground. For example, a table has a square or rectangular base of support defined by its four legs as they touch the floor. As long as an object?s centre of gravity (the effective location of its weight) is above this base of support, the object is statically stable. That stability has to do with the object?s increasing potential (stored) energy as it tips. Tipping a statically stable object raises its centre of gravity and gravitational potential energy, so that it naturally accelerates back toward its upright position. Since a bike has only two contact points with the ground, the base of support is a line segment and the bike can?t have static stability.

But when the bicycle is heading forward, it automatically steers its wheels underneath its centre of gravity. Just as you can balance a stick on your hand if you keep moving your hand under its centre of gravity, a bicycle can balance itself if it keeps mo-ving its wheels under its centre of gravity. This automatic steering has to do with its bending about its steering axis.

In a short, a bicycle is an example of a dynamically stable object. Although it is unstable at rest, it is wonderfully stable when moving forward.

The question was sent by Gajendra Sharma from Bongaon