In what manner should the heel of the hand be utilized during hand sieving?

Using the heel of the hand in an upward motion during hand sieving is essential for achieving better impact on the material being tested. This technique helps in loosening and breaking up any clumps of aggregate, ensuring a more consistent separation of the particles as they pass through the sieve's mesh. By pushing upwards, the heel of the hand generates additional force that aids in this process, enhancing the overall efficiency of the sieving procedure.

In contrast, other techniques mentioned may not provide the optimal results. A downward motion can be less effective as it could compress the material instead of allowing it to flow through the sieve. Gently pressing down might not exert sufficient force to separate particles efficiently. Rotating the hand can also disrupt the sieving process, leading to inconsistent results. Therefore, utilizing an upward motion with the heel of the hand is the most effective method for achieving accurate and reliable results during hand sieving.