STABILITY

The meaning of stability

1. The stability of an object refers to its ability to maintain its original position.
2. An object is said to be stable if it returns to its original position when tilted and released.
3. The greater the angle we have to tilt an object before it topples, the more stable it is.
4. The conical flask in the diagram below is stable because it returns to its original position when it is tilted and released.


5. An object is unstable if it continues to move further than its original position after being tilted and released.
6. The conical flask in the diagram below is unstable because it topples with the slightest tilting.
7. One important factor that affects the stability of an object is its centre of gravity.

Centre of gravity

1. Gravity affects every part of an object. The following diagram shows that gravity pulls on every part of an object.
   
   


2. However, there is one point where the object's whole weight can be considered to concentrate. This point is called the centre gravity of the object.
3. The centre of gravity of an object is defined as the point at which the whole weight of the object seems to act. The following diagram shows that weight acts through the centre of gravity.



4. Regularly shaped objects have their centres of gravity exactly in the middle. The position of centre of gravity in regularly shaped objects is shown in the following diagram.




5. The position of the centre of gravity in irregularly shaped objects is not obvious. Let's look at the position of centre of gravity in some irregularly shaped objects, as shwon in the following diagrams.



6. The centre of gravity of a flat shape can easily be determined by finding its point of equilibrium. The point of equilibrium is the point where the whole weight of an object appears to act on. It is the point in which an object can be balanced on and it is present in all objects.

Factors affecting stability

1. The stability of an object depends on the position of its centre of gravity, and its base area.
2. An object with a lower centre of gravity is more stable than an object with a higher centre of gravity.
3. For example, the quarter and half-filled bottle Q shown in the diagram below is more stable than the empty bottle, P. This is because bottle Q has a lower centre of gravity than bottle P. The water in bottle Q lowers the centre of gravity of the bottle.




4. An object with a larger base area is more stable than an object with a smaller base area.
5. For example, the wooden block S shown in the diagram below is more stable than the wooden block R. This is because wooden block S has a larger area compared to wooden block R.



6. Therefore, an object is more stable if its centre of gravity is lower and its area of base is larger.