Which of the following statements regarding the physical and aerodynamic properties of grain kernels is/are correct?
Options:
(A) Sphericity is defined as the ratio of the diameter of an equivalent sphere of the same volume to the longest diameter of the grain.
(B) Roundness is the ratio of the projected area of the kernel in its natural rest position to the area of the smallest circumscribing circle.
(C) Bulk density is always greater than true particle density for a bed of granular grains.
(D) Terminal velocity occurs when the upward aerodynamic drag force equals the downward buoyant weight of the falling seed.
Answer Key:
A, B, D
Step-by-Step Solution & Explanation
• A is correct: Sphericity $\phi = (a b c)^{1/3} / a$.
• B is correct: Roundness is $A_p / A_c$ where $A_p$ is largest projected area and $A_c$ is area of smallest circumscribing circle.
• C is incorrect: Because granular beds contain void space (porosity $\epsilon$), bulk density is strictly lower than true particle density ($\rho_b = \rho_t(1 - \epsilon)$).
• D is correct: Terminal velocity is attained when aerodynamic drag equals net gravitational force (weight minus buoyancy).