Waves & Optics · Physics

Driving forces create steady response—and resonance.

Learn how amplitude and phase depend on driving frequency, and why damping controls the height and width of resonance.

This topic

Driven Oscillations and Resonance

Separate transient behavior from steady state, then interpret resonance, phase shift, and real-world examples safely and correctly.

Input
External driving forces
Driving adds energy continuously. The key questions are: how much energy per cycle, and how it depends on frequency and phase.
  • What “driving” means physically
  • Periodic forcing intuition
  • Energy added vs energy lost
  • Transient vs steady-state distinction
Response
Steady-state response
After transients fade, the oscillator responds at the driving frequency, not necessarily at its natural frequency.
  • Why transients disappear with damping
  • Response frequency equals driving frequency
  • Amplitude depends on frequency
  • Phase shift emerges naturally
Peak
Resonance condition
Resonance occurs when the driving frequency aligns with the system’s natural tendency to oscillate, producing large amplitude response (limited by damping).
  • Why resonance increases amplitude
  • Damping limits the peak
  • Sharp vs broad resonance
  • Recognizing resonance graphs
Phase
Amplitude and phase relationships
The phase shift tells you whether the oscillator moves in step with the driver or lags behind. Phase changes most rapidly near resonance.
  • In-phase vs out-of-phase meaning
  • Low-frequency vs high-frequency limits
  • Phase behavior near resonance
  • Why phase matters for power transfer
Real
Real-world resonance examples
Resonance appears in bridges, buildings, musical instruments, and electronics. The physics is the same; the safety implications are not.
  • Structural resonance (conceptual)
  • Musical resonance and sound amplification
  • Vibration control and tuning
  • Everyday “resonant response” intuition
Practice
Practice & Exercises
Practice reading resonance curves, describing phase behavior, and connecting damping to response.
  • Identify resonance frequency from graphs
  • Concept checks: damping vs peak width
  • Phase-lag interpretation questions
  • Energy transfer reasoning prompts
  • Exam-style driven-oscillator sets