Questions: Stability and Balance

Question 1

Why is a pyramid one of the most stable structures possible?

• A. Because it is made of heavy stone
• B. Because it has a very wide base and a very low center of gravity
• C. Because the ancient Egyptians were the best engineers
• D. Because triangles are the strongest shape

Answer: (B)

A pyramid has a wide base that gets narrower toward the top. Most of its weight is near the bottom, giving it a very low center of gravity. The center of gravity would have to shift an enormous distance sideways to move outside the wide base. This combination — wide base, low center of gravity — makes pyramids almost impossible to tip over.

Question 2

A structure is stable as long as it is heavy enough.

• T. True
• F. False

Answer: False

Stability depends on the relationship between the center of gravity and the base of support, not on total weight. A heavy object with a high center of gravity and narrow base (like a tall, loaded bookshelf) is less stable than a lighter object with a low center of gravity and wide base (like a low coffee table). Weight alone does not prevent tipping.

Question 3

Explain what happens when a structure's center of gravity moves outside its base of support.

Model answer: The structure tips over. Gravity pulls down on the center of gravity, and when that point is no longer above the base, gravity creates a tipping force that rotates the structure until it falls. The wider the base relative to the height, the harder it is for the center of gravity to move outside the base.

This is the fundamental rule of stability. You can feel it yourself: stand with your feet together and lean sideways — you tip easily. Stand with your feet wide apart and lean — you can lean much farther before tipping because the center of gravity has more room to shift while staying above the base.