Newton's Second Law, One Floor Up

You'll learnthat net torque equals rotational inertia times angular acceleration, the rotational F = ma.

Torque plays force, rotational inertia plays mass, and angular acceleration answers. One dictionary, one law — and the same old trap about zero velocity, wearing a spin.

8 STEPS · 6 QUICK CHECKS · g = 10 m/s² · v5

ROTATION LAB

Before you start

What you're looking at

A disk of rotational inertia 2 kg·m² with a string pulled at 8 N from its rim, 0.5 m out, beside a dictionary panel and an ω-vs-t chart.

The question

How fast does the disk spin up, and which rotational quantity plays the role of mass?

Watch for

The dictionary translating force to torque, mass to rotational inertia, linear to angular acceleration; predict the disk’s response.

What the symbols mean

Στ is net torque, I is rotational inertia, α angular acceleration; the chart plots ω (rad/s) against time (s).

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