Class 11 > Unit # 11:Oscillations > Free, Forced, Damped Harmonic Motion & Resonance

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Types of Oscillations, Resonance & Working of Shock Absorbers

Video Lecture: Oscillations, Resonance & Shock Absorbers

Watch the complete step-by-step video lecture explaining free, forced, and damped oscillations, resonance, and automotive shock absorbers:

Types of Oscillations & Resonance

1. Free Oscillations

Free oscillations occur when a system oscillates with a constant amplitude and period of its own accord, without the influence of any external periodic driving force.

2. Forced Oscillations

When a body is made to oscillate under the direct influence of an external periodic force, its vibrations are referred to as forced oscillations.

3. Resonance

Resonance is a phenomenon that occurs when an external vibrating system drives another system to oscillate with a significantly greater amplitude at a specific matching frequency. This particular frequency is known as the resonant frequency.

4. Damped Oscillations

“The oscillations of a system in the presence of some resistive forces are damped oscillations, and an oscillating system in which friction has an effect is a damped system.”

An oscillating system cannot maintain a fixed amplitude indefinitely unless external energy is continuously supplied. Resistive forces (such as friction or air resistance) progressively reduce the amplitude of oscillation over time. Friction not only diminishes the amplitude but can also slightly reduce the frequency of the system. An oscillation that gradually fades away is called a damped oscillation.

Example: Striking a table causes it to vibrate, but this reverberation/sound fades away after completing numerous cycles due to damping.

Working of Shock Absorbers

A prominent practical application of damped motion is found in automotive shock absorbers.

• Structure: A shock absorber consists of a piston that moves through a viscous liquid (usually specialized hydraulic oil).
• Connection: The upper part of the shock absorber is firmly attached to the frame/body of the automobile.
• Mechanism: When a vehicle travels over a bump or rough road, the car body tends to vibrate violently. The shock absorbers effectively dampen these mechanical vibrations by converting the mechanical kinetic energy into thermal energy within the oil, ensuring a smooth and controlled ride.

Fig: Damping mechanism in automotive shock absorbers.

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