Physics · System Of Particles And Rotational Motion · NEET
No. The COM is a mathematical point, so it can lie outside the material of the body. For a ring, a hollow shell, or a bent rod (like an L-shape or a boomerang), the COM sits in the empty space where there is no matter at all. It is still the point where the whole mass 'effectively' acts, even if nothing is physically there.
No, and this confuses many students. The COM is only a weighted-average position of all the mass. For a uniform ring the COM is at the geometric centre, which is a hole with no metal. So a body can have its COM located at a point with zero mass.
Because it makes a complicated many-particle body behave like ONE simple particle. Instead of tracking millions of atoms, Newton's second law lets you treat the whole body as a single point mass located at the COM. This is why a spinning, tumbling object still has its COM follow a clean parabola when thrown. For NEET, this idea powers momentum, collisions, and rotational-motion problems.
They match ONLY when the body has uniform density (mass evenly spread). The centroid is the pure geometric centre of a shape. The centre of mass is the mass-weighted centre. If the density is uneven, the COM shifts toward the heavier side while the centroid stays fixed at the geometric middle.
They coincide only in a uniform gravitational field, which is nearly always true for small objects on Earth. The COM depends only on how mass is distributed. The centre of gravity is where the total gravitational torque is zero. For NEET-sized objects you can treat them as the same point, but the definitions are different (this exact point was tested in NEET 2017).
Which of the following statements are correct? (a) The centre of mass of a body always coincides with its centre of gravity. (b) The centre of mass is the point where the total gravitational torque on the body is zero. (c) A couple on a body produces both translational and rotational motion. (d) Mechanical advantage greater than one means a small effort can lift a large load.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the single point where the entire mass of a body can be assumed to be concentrated, and it moves as if all external forces act there.
Yes. For a ring, hollow sphere, or L-shaped rod, the COM lies in empty space where there is no material.
COM depends only on mass distribution; centre of gravity is where gravitational torque is zero. They coincide in a uniform gravitational field, which is the usual NEET case.
Exactly at its geometric midpoint, because the mass is spread evenly along its length.
It lets you treat a whole system as one particle, which is the base idea for linear momentum, collisions, conservation laws, and rotational motion, all high-weightage NEET topics.
