Three bottles - one empty, one full of water, and one half-full - are placed on a tilted board to compare their stability. Students observe that the bottle with the lowest center of gravity (the half-full one) is more stable than the empty or full bottles.

1. Add food coloring to water so the mass distribution is more visible.
2. Fill one bottle completely with colored water, leave one empty, and fill another halfway.
3. Tape a pencil to one end of a flat board to act as a stop.
4. Place the three bottles in order (empty, half-full, full) against the pencil lip.
5. Slowly raise the opposite end of the board until the bottles topple.
6. Observe the order in which they fall.

PRACTICAL: Activity to observe stability, tilting and toppling (with explanation) - Physics Rox:

📄 Toppling bottles - IOP: https://spark.iop.org/toppling-bottles

• Try bottles of different shapes (tall vs. short, narrow vs. wide).
• Use sand instead of water for a different mass distribution.
• Compare stability on different surfaces (smooth wood vs. rough cardboard).

• Perform on a stable, flat surface to avoid bottles falling uncontrollably.
• Use plastic bottles to prevent glass breakage.
• Clean up spills promptly to avoid slipping hazards.

• Which bottle toppled first? (The empty and full bottles fell at the same time, while the half-full bottle remained upright longer.)
• Why is the half-full bottle more stable? (Its mass is concentrated lower down, giving it a lower center of gravity.)
• What is meant by the “center of gravity”? (It is the average position where the weight of the object acts.)
• How can you make an object more stable? (Lower its center of gravity or increase the size of its base.)