Physics
Physics
Problem
Two equal-magnitude forces act on a uniform meterstick lying on a frictionless table. The forces are applied perpendicular to the stick at its 10 cm and 90 cm marks and point in opposite directions along the table’s surface. Determine whether the stick is in (i) translational equilibrium and (ii) rotational equilibrium.Intuitive explanation
The key is recognizing that equilibrium has two independent conditions: one about the net force on the center of mass, and one about the net torque around any point. Equal and opposite forces cancel the net force, but they don't automatically cancel torque—that depends on whether they act along the same line. Here, the forces are separated by 80 cm, so they form a couple that creates a net rotational effect even though translation is balanced.
Intuitive explanation
The key is recognizing that equilibrium has two independent conditions: one about the net force on the center of mass, and one about the net torque around any point. Equal and opposite forces cancel the net force, but they don't automatically cancel torque—that depends on whether they act along the same line. Here, the forces are separated by 80 cm, so they form a couple that creates a net rotational effect even though translation is balanced.