Catching Particles at the Bottom of a Volume of Water

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What type of experiment is this?

Experimental procedure and explanation:

• We are going to use a cup to catch tea leaves that have sunk to the bottom of a tank of water.
• First, we tried to catch the leaves with the cup upside down. We were able to catch many of the tea leaves.
  This is because when the cup is submerged in the water, the water close to the rim of the cup is pushed outwards, and only the tea leaves near the edge were carried by this flow and escaped from the cup.
• However, when we tried to catch the leaves with the mouth of the cup upwards, most of the water between the bottom of the cup and the bottom of the tank was pushed out, and many of the tea leaves were carried by this flow and escaped. For this experiment, the cup must have a flat bottom; if the bottom is dented, water will stay inside, and therefore more tea leaves will remain.
• Small, light objects have a tendency to get carried by a flow; this is referred to as having good entrainability. This tendency is due to the effect of the viscosity of the fluid.

[Keywords]	Entrainability, Viscous resistance
[Related items]	Catching Particles Floating in Water, Catching Particles Floating on the Surface of Water
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, P30・・1.