Centre of gravity

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Introduction

The centre of gravity (CG) is a fundamental concept in physics that determines how objects balance, remain stable, or topple over. Understanding the centre of gravity is crucial in engineering, construction, sports, and transportation, where stability is key to safety and functionality.

The centre of gravity

The centre of gravity (CG) of an object is the point where all of its weight appears to act. If an object is supported at this point, it will remain balanced without tipping in any direction.

Key Facts About the Centre of Gravity:

For symmetrical objects (e.g., sphere, cube, cylinder), the CG is at the geometric center.
For irregular objects, the CG does not always lie at the center and must be determined through experiments.
The CG can be located outside the object, as in the case of rings, boomerangs, and hollow shapes.
In moving objects, the CG shifts depending on how the weight is distributed (e.g., a gymnast adjusting their posture).

Examples of the Centre of Gravity in Real Life:

A sports car has a low CG, making it stable around corners.
A double-decker bus has a high CG, making it more likely to topple if it turns too sharply.
A tightrope walker extends their arms or holds a pole to lower their CG and maintain balance.

Experiment to find the centre of gravity

Since irregular objects do not have a predictable centre of gravity, we use an experiment to locate it.

Apparatus:

Irregularly shaped object (thin, flat object like a cut-out piece of cardboard)
Plumb line (a weight tied to a string)
Clamp and stand
Pin and board

Method:

Suspend the lamina from a pin through a small hole near its edge.
Allow the lamina to hang freely.
Hang a plumb line from the same pin.
Draw a vertical line along the string’s position.
Repeat the process by suspending the lamina from a different hole and drawing another vertical line.
The point where the lines cross is the centre of gravity of the object.

Conclusion:

The centre of gravity is the point where the object's weight is evenly distributed, meaning the object can be balanced if supported at this point.

Effect on stability

The position of the centre of gravity plays a crucial role in an object’s stability.

Factors Affecting Stability:

Lower Centre of Gravity = More Stability
- Objects with a low CG (e.g., race cars, wide sports stances) are less likely to topple.
- Example: A bulky backpack makes you less stable because it raises your CG.
Wider Base = More Stability
- Objects with a wide base of support (e.g., a four-legged chair, a sumo wrestler’s stance) are more stable.
- Example: A tripod camera stand is more stable than a one-legged stool.

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