Mean Free Path
Average distance a molecule travels between collisions.
Variables
Derivation
λ = 1/(√2 π d² n) where n = P/(kT).
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Constants in this formula
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- kB = 1.380 649 × 10⁻²³ J/K (Boltzmann constant)
- T = 2 K (Temperature)
- d = 3 m (Molecular diameter)
- P = 4 Pa (Pressure)
Result: λ = 1.726418 × 10⁻²⁵ m
Other thermodynamics formulas with the same quantities
- Ideal Gas Law (Molecular) (Kinetic Theory) shares Pressure, Boltzmann constant, Temperature
- Average Kinetic Energy (Gas) (Kinetic Theory) shares Boltzmann constant, Temperature
- Most Probable Speed (Kinetic Theory) shares Boltzmann constant, Temperature
- Mean Speed (Kinetic Theory) shares Boltzmann constant, Temperature
- Pressure (Kinetic Theory) (Kinetic Theory) shares Pressure
- Stefan-Boltzmann Law (Heat & Temperature) shares Temperature
Where this formula is listed
- Thermodynamics formulas, under Kinetic Theory.
- In the thermodynamics list it comes after Root Mean Square Speed and before Pressure (Kinetic Theory).
- Thermodynamics formula sheet, one of 34 formulas printed with symbol keys and SI units.
- The full formula index, grouped by category and topic.
Common questions
What is the Mean Free Path formula?
Mean Free Path is written λ = (k_B T)/(√(2)πd²P). Average distance a molecule travels between collisions. It belongs to Thermodynamics, under Kinetic Theory.
What are the units in λ = (k_B T)/(√(2)πd²P)?
In SI units, λ is mean free path, measured in m; k_B is boltzmann constant, measured in kg·m²/(s²·K); T is temperature, measured in K; d is molecular diameter, measured in m; P is pressure, measured in kg/(m·s²).
How is the Mean Free Path formula derived?
λ = 1/(√2 π d² n) where n = P/(kT). The result is λ = (k_B T)/(√(2)πd²P).