Question 1

What is angular momentum?

Accepted Answer

Angular momentum (L) is the rotational equivalent of linear momentum. It measures the quantity of rotation of an object and is calculated as L = Iω, where I is the moment of inertia and ω is the angular velocity. Like linear momentum, it is conserved when no external torque acts on the system.

Question 2

Why does an ice skater spin faster when pulling in their arms?

Accepted Answer

Conservation of angular momentum: L = Iω is constant. When the skater pulls in their arms, the moment of inertia I decreases (mass is closer to the axis). To keep L constant, ω must increase, so the skater spins faster. Extending the arms increases I and slows the spin.

Question 3

What is moment of inertia?

Accepted Answer

Moment of inertia (I) is the rotational equivalent of mass. It measures how difficult it is to change an object's rotational motion. It depends on both the mass and how that mass is distributed relative to the rotation axis. Mass farther from the axis contributes more to I (I = Σmr²).

Question 4

How is rotational KE different from linear KE?

Accepted Answer

Rotational KE (½Iω²) is the kinetic energy due to spinning, while linear KE (½mv²) is due to straight-line motion. A rolling ball has both: it translates and rotates simultaneously. The total KE is the sum of both components.

Question 5

What are the units of angular momentum?

Accepted Answer

Angular momentum is measured in kg·m²/s (kilogram-meters-squared per second) in SI units. This is equivalent to J·s (Joule-seconds) or N·m·s (Newton-meter-seconds). In quantum mechanics, angular momentum is quantized in units of ħ (reduced Planck constant ≈ 1.055 × 10⁻³⁴ J·s).

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