What Is Critical Speed?

Charlotte Miller

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Are you curious to know what is critical speed? You have come to the right place as I am going to tell you everything about critical speed in a very simple explanation. Without further discussion let’s begin to know what is critical speed?

In the world of engineering, mechanics, and physics, the term “critical speed” is used to describe a phenomenon that can have significant implications in various applications, from engineering and transportation to sports and music. This blog aims to provide a comprehensive understanding of what critical speed is, how it is calculated, and its practical significance in different fields.

What Is Critical Speed?

Critical speed, also known as the “resonant speed” or “whirling speed,” is the speed at which an object or system naturally vibrates or oscillates. When an object is subjected to a force that induces vibration or oscillation, it has one or more natural frequencies at which it tends to vibrate most strongly. These frequencies are determined by the object’s mass, shape, and material properties.

The concept of critical speed is particularly important in various fields, such as:

  1. Mechanical Engineering: Critical speed is crucial in mechanical systems, especially rotating machinery like shafts, turbines, and rotors. When a mechanical component operates near its critical speed, it can lead to resonance and potentially catastrophic failure.
  2. Civil Engineering: Bridges, buildings, and other structures can experience resonance due to wind or seismic forces. Engineers must consider critical speeds to prevent destructive oscillations.
  3. Sports: Athletes and sports equipment, such as tennis racquets or golf clubs, can experience critical speed. Understanding these dynamics can help improve performance.
  4. Music: Musical instruments, like strings and reeds, have critical speeds that affect the sound produced. Musicians must consider these factors for optimal performance.

Calculating Critical Speed

The formula for calculating the critical speed of an object or system varies depending on the specific situation. However, the basic equation for critical speed in rotational systems is:

Critical Speed (N) = (C / 2π) * √(Tension / Mass per unit length)


  • C is the constant depending on the boundary conditions (e.g., fixed or free ends).
  • Tension represents the tension in the system.
  • Mass per unit length is the mass per unit length of the object or system.

In structural engineering, the critical speed of a structure under lateral vibration due to wind or seismic forces is determined by complex mathematical modeling and finite element analysis.

Significance Of Critical Speed

Understanding and managing critical speed is crucial for several reasons:

  1. Avoiding Resonance: Operating a system near its critical speed can lead to resonance, which causes excessive vibration and structural fatigue. Preventing resonance is essential to maintain the structural integrity of machinery and structures.
  2. Enhancing Performance: In sports and music, athletes and musicians can use knowledge of critical speed to optimize their techniques and equipment to achieve better performance.
  3. Safety: In transportation, critical speeds are critical for vehicle design and safety. Ensuring that vehicles can safely operate at various speeds is essential for passenger safety.
  4. Energy Efficiency: Optimizing machinery to avoid critical speed can improve energy efficiency and reduce maintenance costs.


Critical speed is a fundamental concept that plays a vital role in various fields, from engineering and transportation to sports and music. Understanding the natural frequencies of objects and systems allows us to design and operate them safely and efficiently. Whether it’s preventing resonance in machinery, improving athletic performance, or creating beautiful music, critical speed is a key factor that should not be underestimated.


What Do You Mean By Critical Speed?

Critical speed (nk) is the rotational speed at which acting dynamic forces cause a machine component (e.g. shaft, rotor) to vibrate at its natural frequency (also referred to as intrinsic frequency, fi) and can even result in resonant vibrations throughout the entire machine and pump set.

What Is The Critical Speed In Physics?

The branch of mechanics known as rotordynamics defines critical speed as the angular velocity that excites the natural frequency of some rotating object. In the case of a pump shaft, it is the measured rotational speed where natural vibration occurs.

What Is Critical Speed In Shaft Design?

The critical or whirling speed is the speed at which the shaft travels so that the extra deviation of the post from the axis of rotation becomes infinite.

What Is First Critical Speed?

The lowest rotational speed at which this natural vibration occurs is called the first critical speed. Resonance is not often a concern when short, rigid shaft pumps are operated at their design speed. Even if a natural frequency resides between zero and full speed, it is passed quickly during starting.

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