10. A spinning-top is spun anticlockwise (when seen from above). As the top slows
down it starts precessing, i.e. its axis of rotation starts revolving around the vertical.
What is the direction of this precession when seen from above?
a. clockwise
b. anticlockwise
c. depends on whether you are in the northern or southern hemisphere
d. depends on the type of surface the top is spinning on
Spinning Top Precession Direction: Anticlockwise Spin Explained
A spinning top spun anticlockwise from above precesses clockwise when viewed from above as it slows down, due to gravitational torque acting on its angular momentum. This makes option (a) clockwise the correct answer.
Question Breakdown
The scenario describes a top with initial anticlockwise spin (counterclockwise rotation about its axis). Gravity produces torque perpendicular to the lean, causing the angular momentum vector to change direction horizontally rather than falling over. For anticlockwise spin, this torque results in clockwise precession around the vertical axis, independent of location or surface.
Option Analysis
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a. Clockwise: Correct. Torque from the top’s weight acts to topple it, but spin angular momentum L⃗ (pointing upward for anticlockwise spin via right-hand rule) precesses such that dL⃗dt=τ⃗ (torque) directs motion clockwise from above.
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b. Anticlockwise: Incorrect. This would occur for clockwise initial spin, reversing the angular momentum direction and precession sense.
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c. Depends on hemisphere: Incorrect. Precession follows local physics of torque and spin, not Coriolis effects or Earth’s rotation, which are negligible for a tabletop top.
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d. Depends on surface: Incorrect. Precession arises from gravity and friction at the pivot; surface type affects spin decay but not steady precession direction.
