Short Answer:

Vibration is the back-and-forth or oscillating motion of a body about its mean or equilibrium position. It occurs when a body is displaced from its original position by an external force and then tries to return to that position due to the restoring force. This continuous motion results in periodic movement known as vibration.

In mechanical systems, vibration is very common and can be both useful or harmful. Controlled vibrations are used in machines like shakers or musical instruments, while excessive vibrations in engines, machines, or structures can cause damage, noise, or reduced efficiency.

Detailed Explanation :

Vibration

Vibration is the repetitive or periodic motion of an object about its equilibrium position. In simple terms, it is the continuous to-and-fro movement of a body due to the action of external or internal forces. The equilibrium position is the point where the object remains at rest when no external force is acting on it. Once displaced from this position, the body experiences a restoring force that tries to bring it back, and this results in oscillatory motion.

For example, when a tuning fork is struck, its prongs move back and forth rapidly — this is a vibration. Similarly, the piston in an engine, the blade of a fan, or the bridge under traffic load all undergo vibration to some extent.

1. Causes of Vibration

Vibration occurs due to an imbalance between applied forces and restoring forces in a system. The main causes of vibration include:

• Unbalanced forces: When rotating parts like shafts or rotors have unequal mass distribution, unbalanced centrifugal forces cause vibration.
• Elastic properties: Elastic bodies like springs and beams vibrate when deformed and released.
• External excitation: Periodic forces applied externally, such as those from machinery or engines, cause forced vibration.
• Resonance: When the frequency of external excitation matches the natural frequency of a body, large amplitude vibrations occur.
• Mechanical faults: Loosened joints, misalignments, or worn-out parts can lead to irregular vibrations in machines.

2. Types of Vibration

There are mainly three types of vibration observed in mechanical systems:

(a) Free Vibration:
It occurs when a body vibrates freely after an initial disturbance without any external force acting continuously. The frequency of free vibration depends only on the system’s properties such as mass and stiffness. Example: A plucked string of a guitar vibrates freely.

(b) Forced Vibration:
It takes place when an external periodic force acts on the system, keeping it in continuous vibration. Example: A motor mounted on a flexible base experiences forced vibration due to unbalanced rotating parts.

(c) Damped Vibration:
When the amplitude of vibration gradually decreases due to friction or resistance, it is called damped vibration. Damping is introduced to control vibration amplitude and prevent damage to components. Example: Shock absorbers in vehicles use damping to reduce vibrations.

3. Parameters of Vibration

To study vibration, some basic terms are important:

• Amplitude: Maximum displacement of a vibrating body from its equilibrium position.
• Frequency: Number of cycles completed per second, measured in hertz (Hz).
• Period: Time taken for one complete cycle of vibration.
• Natural Frequency: The frequency at which a system tends to vibrate when disturbed.
• Phase: Describes the position of the vibrating body at a particular instant relative to a reference point.

These parameters help in understanding the motion characteristics of a vibrating system.

4. Effects of Vibration

Vibration has both positive and negative effects depending on its nature and intensity:

• Useful Effects: Controlled vibration is used in vibrating screens, compactors, ultrasonic machines, and musical instruments. It helps in various manufacturing and testing processes.
• Harmful Effects: Uncontrolled or excessive vibration can lead to noise, wear and tear of components, fatigue failure, and discomfort to humans. It reduces machine life and efficiency.

Hence, engineers aim to minimize unwanted vibrations through proper design, balancing, and damping techniques.

5. Control of Vibration

To reduce unwanted vibrations in mechanical systems, several methods are used:

• Balancing: Ensuring even mass distribution in rotating parts to avoid unbalanced forces.
• Damping: Using shock absorbers, rubber mounts, or viscous dampers to absorb vibration energy.
• Isolation: Mounting machines on vibration isolators to prevent transmission of vibrations.
• Tuning: Adjusting the natural frequency of the system so that it does not match the excitation frequency.

These techniques help in maintaining stability, comfort, and durability of machines and structures.

Conclusion

Vibration is the periodic back-and-forth motion of a body about its equilibrium position caused by external or internal forces. It plays an important role in mechanical systems, where controlled vibrations are beneficial and uncontrolled ones are harmful. Understanding and controlling vibration is crucial to ensure smooth machine operation, reduce noise, prevent structural failure, and enhance performance. Thus, vibration analysis and control are essential parts of mechanical engineering design.