Subtopic: Angle of repose and frictional flowability
Question Statement:
Which of the following statements regarding the physical and frictional properties of agricultural grains is/are TRUE?
Options:
(A) As moisture content of grains increases, the angle of repose generally increases due to higher surface cohesion
(B) Dynamic coefficient of friction is always lower than or equal to static coefficient of friction against a given surface
(C) True density is determined by air/gas pycnometer or toluene displacement, excluding inter-particle void volume
(D) Bulk density of grains is always strictly greater than true density
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. Moisture increases capillary surface cohesion, steepening the pile angle of repose (A is true).
2. Kinetic friction is lower than static friction $\mu_k \le \mu_s$ (B is true).
3. Pycnometry excludes inter-seed voids to measure solid grain kernel density (C is true).
4. Bulk density includes air voids, so bulk density is always substantially LESS than true density ($\rho_b < \rho_t$) (D is false).