Why can't a bicycle stand up?

Answer 1

One first has to assume you mean 'unaided, as without the use of a kickstand'.
The answer is: It can, but only if it is perfectly balanced - which is possible - but only if all external influences are eliminated, those outside influences being earth movement (which is constant, but imperceptible) and air movement. While it is feasible to eliminate air movement (place it in an enclosed warehouse, for instance), there is no place on earth that is perfectly stable.
So, while the technical answer is 'Yes', the realistic answer is 'No'.

Answer 2

The same forces that keep a gyroscope upright are the ones that keep your bicycle upright. When the wheel is not spinning, the gyroscope falls over. When the bicycle's wheel is not turning, the bicycle falls over for the same reason.

The physics of gyroscopes are too complex to discuss on this board. If you want, you can find more detail at http://en.wikipedia.org/wiki/Gyroscope.

HTH

Answer 3

Because the 2 points of contacts, being the wheels, are in the same verticle plane. There needs to be another point of contact in a different plane, making it 3 dimensional. The same reason you can't stand up a single sheet of wood or cardboard w/o some support on either side.

Answer 4

it could if you balanced it right... in theory.

but in real life you can make it balance (and stand still) by doing a "track stand"

most track stands are done on fixed gears, it makes it easier, but you can do one on a freewheel bike too, with practice.

Answer 5

Because it is two tired.
:)

Answer 6

because the wheels are rounded...

Answer 7

that is just a dumb question

Answer 8

Quite simple... because it has no legs... DUH!