IAS Gyan

Daily News Analysis


8th February, 2024 Science and Technology


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The Indian Institute of Technology Kanpur (IITK) has achieved a significant milestone by establishing and testing India’s first Hypervelocity Expansion Tunnel Test Facility, named S2.


  • Capabilities of S2:
    • The S2 facility is capable of generating flight speeds between 3-10 km/s.
    • It simulates hypersonic conditions encountered during various scenarios, including atmospheric entry of vehicles, asteroid entry, scramjet flights, and ballistic missiles.
    • The facility is essential for ongoing missions of ISRO and DRDO, including Gaganyaan, RLV, and hypersonic cruise missiles.
  • Location and Nickname:
    • S2, nicknamed 'Jigarthanda', is situated at IIT Kanpur’s Hypersonic Experimental Aerodynamics Laboratory (HEAL) within the Department of Aerospace Engineering.
    • The 24-meter-long facility is a testament to indigenous design and development over three years.
  • Support:
    • Funding and support were provided by the Aeronautical Research and Development Board (ARDB), the Department of Science and Technology (DST), and IIT Kanpur.

Introduction to Sonic Speeds

  • Sonic speed, also known as the speed of sound, is the rate at which sound waves propagate through a medium.
  • It is a fundamental property influenced by the properties of the medium, such as its density, elasticity, and temperature.

Factors Affecting Sonic Speed:

  • Medium: The speed of sound varies depending on the medium through which it travels, such as air, water, or solids.
  • Temperature: In gases, the speed of sound increases with temperature due to increased molecular motion, while in liquids and solids, it generally increases with temperature but to a lesser extent.
  • Pressure: Changes in pressure affect the density and compressibility of the medium, thus impacting the speed of sound.
  • Humidity: Moisture content in the air can affect its density and thus influence the speed of sound.

Significance and Effects of Sonic Speeds:

  • Aeronautics: Understanding sonic speeds is crucial in aviation for determining aircraft performance, including takeoff, landing, and the formation of shock waves during supersonic flight.
  • Meteorology: Sonic speeds influence atmospheric phenomena such as the propagation of sound waves, the formation of thunderstorms, and the behavior of weather fronts.
  • Underwater Acoustics: In underwater environments, the speed of sound affects communication, navigation, and the detection of underwater objects.
  • Material Testing: Sonic speeds are used in non-destructive testing techniques like ultrasonic testing to detect flaws or defects in materials.
  • Medical Imaging: Ultrasonic imaging techniques utilize the speed of sound to create images of internal body structures in medical diagnostics.

Applications of Sonic Speeds:

  • Supersonic and Hypersonic Flight: Sonic speeds play a crucial role in the design and operation of supersonic and hypersonic aircraft, including military jets and experimental spaceplanes.
  • Sonar Systems: Underwater sonar systems utilize the speed of sound to detect and locate objects underwater, including submarines, marine life, and geological features.
  • Ultrasonic Cleaning: Ultrasonic cleaners use high-frequency sound waves to remove dirt and contaminants from surfaces in industrial and household applications.
  • Acoustic Levitation: Sonic speeds are used in acoustic levitation techniques to suspend and manipulate objects without physical contact, with applications in materials science and microgravity research.

Speed of Sound in Air:

  • The speed of sound in air varies with temperature, humidity, and pressure.
  • At room temperature (around 20°C or 68°F), the speed of sound in dry air is approximately 343 meters per second (m/s) or 1,235 kilometers per hour (km/h).
  • As temperature increases, the speed of sound in air also increases, due to the increased molecular motion. 

Speed of Sound in Water:

  • The speed of sound in water is much faster than in air, as water is denser and more elastic.
  • At room temperature, the speed of sound in water is about 1,480 m/s (approximately 5,350 km/h), which is about four times faster than in air.
  • The speed of sound in water also varies with factors such as temperature, salinity, and pressure.

Speed of Sound in Solids:

  • Sound travels even faster through solids due to their higher density and elasticity.
  • The speed of sound in solids varies depending on the material.
    • In steel, the speed of sound can range from about 5,900 m/s (21,240 km/h) to 6,700 m/s (24,120 km/h).
    • In diamond, it can be as high as 12,000 m/s (43,200 km/h) or more.

Supersonic Speed:

  • Supersonic speed refers to speeds faster than the speed of sound in the medium.
  • In air at sea level conditions, this is typically speeds greater than about 343 m/s (approximately 1,235 km/h).
  • Aircraft traveling at supersonic speeds generate shock waves and can produce a characteristic "sonic boom."

Hypersonic Speed:

  • Hypersonic speed refers to speeds significantly faster than the speed of sound.
  • In the context of atmospheric flight, hypersonic speeds are generally considered to be speeds greater than Mach 5 (five times the speed of sound) or about 1,715 m/s (approximately 6,174 km/h).
  • Hypersonic flight presents significant engineering challenges due to extreme temperatures, aerodynamic heating, and shock wave interactions.

Transonic Speed:

  • Transonic speed refers to speeds near the speed of sound, where airflow around an object begins to approach and exceed the speed of sound.
  • In aerodynamics, transonic flight occurs in the range of Mach numbers from about 0.8 to 1.2.
  • At transonic speeds, airflow phenomena such as shock waves, compressibility effects, and drag divergence become significant.


Q. Which of the following statements regarding sonic speeds is correct?

1. Sonic speed refers to the speed of light in a vacuum.

2.  Sonic speed is the maximum speed attainable by any object in motion.

3.  Sonic speed is the speed at which sound waves propagate through a medium.

4.  Sonic speed is inversely proportional to the density of the medium.


A) 1 and 2

B) 2 and 3

C) 3 and 4

D) 1 and 4

Correct Answer: C)