MEMORY ENHANCER

1. The ________ is the point where the whole weight of an object appears to act on.
   
2. The ________ of an object refers o its ability to maintain its original position.
   
3. The point of equilibrium of an object is actually the ________ of the object.
   
4. An object is said to be _______ if it returns to its original position when tilted and released.
   
5. An object is _________ if it continues to move further than its original position after being tilted and released.
   
6. Factors affecting the stability of an object are _________ and ________.
   
7. We are more stable when we are standing with our legs apart because the centre of gravity is ________ and the base area is ___________.
   
8. An old man increases his stability by using a __________.
   
9. Laboratory apparatus such as Bunsen burner, retort stand, tripod stand and measuring cylinder have __________ to increase stability.
   
10. Extra __________ are attached to children'c bicycle to increase their stability.

APPRECIATING THE IMPORTANCE OF STABILITY

Improving

1. When an object is tilted, it will start to topple over when the action line of its weight through its centre of gravity falls outside the base. This is as shown in the following diagram.

   


2. There are two ways to make an object more stable by lowering its centre of gravity which can be done either by reducing its height or attaching a heavy weight onto its base and increasing its base area.
3. In both ways, the action line of the weight through the centre of gravity falls within the base unless the object is tilted by a very large angle. The following diagram shows to improve the stability of a box.

Applying the principle of stability

1. Stability is very important to us. The use of unstable object would lead to accident. There will be great losses of property and lives if the object around us were to toppleover exactly.
2. There, the principle of stability is widely used in designing buildings, vehicles, furniture and appliances. They are designed to have a low centre of gravity and a larger base area for stability purposes.

• The buildings, houses, schools and factories are usually built on a heavy concrete foundation for stability. This lowers the centre of gravity of the building.

• A racing car is built low so that it has a low centre of gravity. Its tyre are wide and set apart to give the car a large base area.
• Lorries, trucks, buses and double-decker buses are designed with their heavy engines as near to the ground as possible to lower their centres of gravity.
• Furniture such as cupboards, tables and chairs are made more stable by having broad legs or legs that are set wide apart.
• The bottom of a glass is thicker and heavier to lower its centre of gravity.
• Many electrical appliances such as table lamps, standing fans and Bunsen burners are designed with a larger and heavy base.
• Laboratory apparatus such as tripod stands, conical flasks and measuring sylinders have a larger base area.
  

3. In fact, we also apply the principle of stability in many of aour daily activities.

• When arranging items in a tall shelf, we arrange the heavier items at th bottom shelves.
• An old person will bend forward and use a walking stick to make himself more stable while walking.
• Boxers and people who practice martial arts such as karate always stand with their feet wide apart and their body low when fighting.
• The passengers of double-decker bus are not allowed to stand on the upper deck so that the centre of gravity of the bus is not raised.

EXPERIMENT

Finding out how the centre of gravity and base area affect the stability of objects

1) Hypothesis
The lower the centre of gravity, the more stable the object

2) Materials / apparatus:
Palsticine, matchsticks, wooden plank and scissors

3) Procedure

• Models P, Q and R are built by using 100g plasticine and four matchsticks each.
• The matchsticks are stacked to plasticines.
• The three models are placed on a wooden plank.
• One end of the wooden plank is slowly lifted up and the sequence in which the models
  topple is observed.

4) i. Observation

• Model R, which is the tallest, topples first. This is followed by model Q and finally model P.

ii. Inference

• Model P is the most stable, followed by model Q. Model R is the least stable.

5) Discussion:

• In this experiment, the position of the centre of gravity is manipulated by varying the
  height of the models. The shorter the model, the lower the centre of gravity.
• Therefore, model P has the lowest centre of gravity, followed by model Q and finally model R.

6) Conclusion:
The lower the centre of gravity, the more stable the model. The hypothesis is accepted.

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.