Define centre of gravity and line of gravity.

Concept understanding — Center of Mass Stability

Center of Mass Stability

Think about a toddler learning to walk. They stand with their feet wide apart, arms out, wobbling. They fall often. Now think of a sumo wrestler — low to the ground, legs spread, solid as a rock. What's the difference? It's not just practice. It's physics, and the key idea is center of mass stability.

The Intuition: The Balancing Point

Every object, including your own body, has a single point where its entire weight seems to be concentrated. That point is the center of mass. For a perfectly symmetrical object like a ball, it's right at the geometric center. For a human standing straight, it's roughly around your navel.

Now, stability is about whether that point stays inside your base of support — the area beneath you that is in contact with the ground. If your center of mass moves outside that base, you tip over. That's why a toddler falls: their center of mass is high (they're tall relative to their width) and their base is narrow (feet close together). A slight lean shifts the center of mass past their feet, and gravity does the rest.

Note

The base of support isn't just the area of your feet. If you use a walking stick, your base expands to include the area between your feet and the stick's contact point. That's why a stick helps you balance — it enlarges your stable zone.

What Makes Something Stable?

Three factors determine how stable an object is:

Height of the center of mass: Lower is more stable. A racing car is built low to the ground so it doesn't flip in a sharp turn. A tall lamp is easy to knock over because its center of mass is high.
Size of the base of support: Wider is more stable. A four-legged chair is harder to tip than a two-legged one. A person standing on one leg is less stable than on two.
Position of the center of mass relative to the base: The closer it is to the center of the base, the more stable. If you lean forward while standing, your center of mass moves toward the front of your feet. Lean too far, and you must step forward to catch yourself — you've moved your base under your shifting center of mass.

Important

Stability is not about being heavy. A heavy object with a high center of mass and a narrow base can be less stable than a light object that is low and wide. Think of a heavy vase on a thin pedestal versus a light, flat book on a table.

Why It Matters in Everyday Life …

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Centre of gravity is the point where the body’s total weight acts; line of gravity is the vertical line through that point. Together they determine stability.

The centre of gravity (COG) is the imaginary point in a body where the entire weight is considered to be concentrated. For a uniform object, it lies at its geometric centre; for the human body, it shifts with posture and is roughly at the level of the second sacral vertebra when standing upright. The line of gravity (LOG) is the vertical line that passes through the centre of gravity straight down toward the ground.

Why does this matter? Stability — whether you’re standing, walking, or performing a yoga asana — depends on where the line of gravity falls relative to the base of support. The base of support is the area beneath the body that is in contact with the ground. If the line of gravity falls within the base of support, the body is stable; if it falls outside, the body will topple or need to take a step to regain balance.

Note

A wider base of support and a lower centre of gravity both increase stability. That’s why a wrestler’s crouch is more stable than standing tall on tiptoes. …

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Q.Define centre of gravity and line of gravity.

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