Edexcel iGCSE Physics -1.31P Centre of Gravity- Study Notes- New Syllabus

Centre of Gravity

The centre of gravity of a body is the point through which the entire weight of the body appears to act.

For an object in a uniform gravitational field, the centre of gravity is the same as the centre of mass.

Weight and Centre of Gravity

The weight of a body always acts vertically downward through its centre of gravity.

• Weight acts as a single force.
• The line of action passes through the centre of gravity.
• This applies whether the object is moving or stationary.

Key Formula

The weight of a body is given by:

\( \mathrm{W = mg} \)

• \( \mathrm{W} \) = weight (N)
• \( \mathrm{m} \) = mass (kg)
• \( \mathrm{g} \) = gravitational field strength (N/kg)

The force \( \mathrm{W} \) acts through the centre of gravity.

Centre of Gravity in Different Objects

• For a regular, uniform object, the centre of gravity is at its geometric centre.
• For an irregular object, the centre of gravity may be outside the object.
• For objects with uneven mass distribution, the centre of gravity shifts toward the heavier part.

Centre of Gravity and Stability

• An object is stable when the line of action of its weight passes through its base.
• If the line of action falls outside the base, the object topples.
• Lower centre of gravity increases stability.

Finding the Centre of Gravity

For a flat object:

• Suspend the object from one point.
• Draw a vertical line downwards.
• Repeat from another point.
• The intersection gives the centre of gravity.

Key Idea

• Weight acts through the centre of gravity.
• The centre of gravity determines balance and stability.
• Its position depends on shape and mass distribution.

Important Points to Remember

• Weight always acts vertically downward.
• Centre of gravity is not always inside the object.
• Stability depends on the position of the centre of gravity.