# Stability

Stability describes the ability of a body or device to maintain a given position, property or performance over a given period of time.
Not to be confused with stamina .

## mechanical engineering

In mechanical engineering, stability is generally understood to mean the ability of machines to provide a desired nominal output over longer periods of time without defects or special maintenance measures. In the case of powerful internal combustion engines in particular, this means being able to sustainably demand the maximum output.

## Stability of equilibrium

The position of its center of gravity in relation to the support surface is decisive for the stability of a body . A body remains only stand on its support surface when the emphasis lot she meets, that is, when the contact surface under the center of mass is located. If this is not the case, the body falls over.

The stability is important in structural engineering, for example for buildings , towers, masts , cranes or shelves . A stable equilibrium must be ensured in all of these examples .

Stable
A body is in stable equilibrium when it returns to its stable position after a slight deflection . A body in a stable equilibrium receives a higher positional energy with every deflection . This is the case, for example, with a body that rests on a plane with a contact area when the perpendicular through the body's center of mass intersects the plane within the contact area. In addition, in stable equilibrium, the point of support is above the center of gravity (example: a hanging body).
Unstable
A body is in an unstable equilibrium if it moves further away from the unstable equilibrium after being slightly deflected. A body that is in an unstable equilibrium receives a lower positional energy with each deflection and its support point is below the center of gravity. If the support point is not within the standing or support surface, the body will tip over as soon as it is moved slightly.
Indifferent
A body is in an indifferent equilibrium if it maintains its position after a slight deflection, i.e. neither overturns nor returns to its original state. For a body in an indifferent equilibrium, the positional energy is constant with every deflection. This is the case if the center of gravity of the body does not change when moving relative to the support, for example a wheel that can rotate on an axis.

### Dimensions for stability

A measure of stability is the amount M of the torque that has to act on the body in order to overturn it:

${\ displaystyle M = {G \ cdot l}}$ .

Meaning of the symbols:

${\ displaystyle M}$- Amount of torque that has to act to overturn the body, - Weight of the body, - Distance of the center of mass from the tilting edge.
${\ displaystyle G}$
${\ displaystyle l}$

From this formula it can be concluded that the stability is greater, the lower the center of gravity of the body is and the greater its weight.