Question

rotational dynamics and static equilibrium conceptual questions
prelecture video: static equilibrium and center of mass

click play to watch the video. answer the ungraded questions in the video and the graded follow-up questions at right.

part a
an extended object is in static equilibrium if

• only the net torque acting on the object is zero
• only the net force acting on the object is zero
• either the net force acting on the object is zero or the net torque acting on the object is zero
• both the net force acting on the object is zero and the net torque acting on the object is zero

Explanation:

Define conditions for static equilibrium

$$ \sum \vec{F} = 0 \quad \text{and} \quad \sum \vec{\tau} = 0 $$

Match conditions to options

The definition of static equilibrium for an extended object requires both the net force to be zero (to prevent translational acceleration) and the net torque to be zero (to prevent rotational acceleration).

Answer:

• only the net torque acting on the object is zero
• only the net force acting on the object is zero
• either the net force acting on the object is zero or the net torque acting on the object is zero
• both the net force acting on the object is zero and the net torque acting on the object is zero (Correct answer)