Consider a rectangular block of wood moving with a velocity vo in a gas at temperature T and mass density ρ. Assume the velocity is along the x-axis and the area of the cross-section of the block perpendicular to vo is A. Show that the drag force on the block is
, where m is the mass of the gas molecule.
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Let ρm is the no.of molecules per unit volume
Change in momentum by a molecule on front side = 2m (v + v0)
Change in momentum by a molecule on backside = 2m (v – v0)
No.of molecules striking front side = 1/2 [A(v+v0)∆t] ρm
No.of molecules striking back side = 1/2 [A(v-v0)∆t] ρm
Solving the above equation by considering the KE of the gas molecule, we get the dragging force as 4m A ρmv0√kgT/m
Some of the different macroscopic properties of gases, which can be explained with the help of kinetic theory are, listed below:
- Pressure
- Temperature
- Viscosity
- Thermal Conductivity
- Volume
Important Topics Covered in Chapter 13 Kinetic Theory
- Molecular nature of matter
- Behaviour of gases
- Kinetic theory of an ideal gas
- Law of equipartition of energy
- Specific heat capacity
- Mean free path