Center of Gravity

What is centre of gravity?

It is the point through which its whole weight appears to act.

• Regular objects have their CG at the center of the object.
• Objects are balanced when their CG is directly above or below a pivot or its base.

Classic Center of Gravity Questions

1. Describe an experiment to locate the center of gravity of an irregular shaped lamina.

• Make 3 small holes, as far apart as possible, near the edge of the card.
• Suspend the card through one of the holes using a pin.
• Hang a plumbline from the pin in front of the card.
• When the plumbline is steady, draw the vertical line on the cardboard as indicated by the plumbline.
• Repeat the above for two other holes.
• The point of intersection of the three lines is the position of the center of gravity of the cardboard (lamina).

2. For any free hanging object, the center of gravity must be vertically below the pivot. Explain.

• When the CG is vertically below the pivot, the perpendicular distance between the line of action of the weight to the pivot is zero.
• Since the perpendicular distance between the force and the pivot is zero, the resultant moment will also be zero and the object does not turn.