Why does a pendulum eventually stop?
Show answer & explanation
Answer: Air resistance and friction
String stretches over time — Wrong. String stretch is minimal. Pendulum stops because air resistance and friction convert kinetic energy to heat.
Weight becomes lighter — Wrong. Weight doesn't change. Energy dissipates through air resistance and friction at pivot point, gradually stopping pendulum.
Air resistance and friction ✓ — Correct! Ideal pendulum (no friction/air resistance) swings forever—conservation of energy. Real pendulums lose energy: (1) Air resistance—pendulum pushes air molecules, loses kinetic energy to heat. (2) Pivot friction—bearing resistance. Energy converts to heat. Amplitude decreases each swing—damped oscillation. Eventually stops. Grandfather clocks have weights/springs adding energy to compensate losses. Vacuum + frictionless bearing = pendulum swings for days!