Whenever the centre of gravity in it has to be lifted up in order to make the change, as is shown in [Fig. 35].
Fig. 33.
Fig. 34.
Fig. 35.
The centre of gravity, in [Fig. 33], may be lowered; hence, it will change its position if unsupported. The centre of gravity, in [Fig. 34], can neither be lowered nor lifted up; hence, it may be readily rolled about. The centre of gravity, in [Fig. 35], must be lifted up; hence, it remains firm in its place.
When does an object stand firm?
It stands firm when it has a broad base, and its centre of gravity is near the earth.