In the centre of mass experiment with a lamina, how should you view the string to determine balance?

• A. View the string directly in front of the card.
• B. View the string from the side.
• C. View the string through a mirror.
• D. View the string at an angle.

Answer: (A)

Seeing whether the lamina is balanced hinges on the string hanging exactly vertical, because the center of mass must align with the suspension point so there’s no tipping torque. Looking straight at the string in front of the card minimizes parallax error, letting you judge whether it is truly vertical. If you view from the side, at an angle, or through a mirror, perspective effects can fool you and make a non-vertical string look vertical or vice versa. So you balance by watching the string directly from the front to confirm the string is vertical and the lamina is balanced.