Question

An ideal pendulum is often discussed when studying simple harmonic motion.

What are the conditions needed for an ideal pendulum? Check all that apply.

Gravitational force acts to pull the pendulum’s mass down.
The mass of the rod of the pendulum is evenly distributed along the rod.
The pivot on which the pendulum swings is frictionless.
The pendulum swings through its equilibrium position as a result of inertia.
Tension acts downward on the pendulum’s mass

Answer 1

Select:
- Gravitational force acts to pull the pendulum’s mass down. — Yes. An ideal pendulum assumes a uniform gravitational field producing the restoring component of force.
- The pivot on which the pendulum swings is frictionless. — Yes. No pivot friction is assumed so energy is conserved and motion is simple harmonic (aside from small-angle requirement).
- The pendulum swings through its equilibrium position as a result of inertia. — Yes. At equilibrium the restoring torque is zero, so the bob continues through by virtue of its momentum.

Do not select:
- The mass of the rod of the pendulum is evenly distributed along the rod. — No. An ideal pendulum usually treats the rod/string as massless and the mass concentrated in a point bob.
- Tension acts downward on the pendulum’s mass. — No. Tension acts along the string toward the pivot (not vertically downward in general).