ROTATIONAL MOTION

In the case of a rod with equal and opposite forces applied perpendicularly at its ends, why does pure rotation occur?

• The rod is pivoted at the center
• Gravity balances the forces
• Net force is zero, so no translation; net torque is non-zero, causing rotation
• The air resistance stops translation

What is the main reason a light rod with equal parallel forces at its ends in the same direction does not rotate?

• The forces are too small
• The rod is too heavy
• The forces act along the same line
• The torques produced by the forces are equal and opposite, resulting in zero net torque

How is mechanical equilibrium different for a rigid body compared to a particle?

• There is no difference
• A rigid body requires only torque balance
• A rigid body requires both force and torque balance, while a particle needs only force balance
• A particle requires torque balance

What is the effect of increasing the distance between forces in a couple?

• Decreases torque
• Has no effect
• Increases the mass
• Increases the torque

Why do forces on a compass needle form a couple when not aligned?

• Because the needle is magnetic
• Because forces are unequal
• Because they act at different points and are not collinear
• Because the Earth rotates