I keep getting “Centre of mass” questions wrong in Rotational Motion. What's the trap?
assuming it always lies inside the body (for a ring it's at the empty centre).
The usual trap: assuming it always lies inside the body (for a ring it's at the empty centre). How to avoid it: for symmetric bodies it sits at the geometric centre. Go back to the definition — the single point where the whole mass of a system can be treated as concentrated.
Key point
Centre of mass
Common mistake
assuming it always lies inside the body (for a ring it's at the empty centre).
Memory tip
for symmetric bodies it sits at the geometric centre.
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