If you pour water into a sieve held above a bowl, the water will pass through the holes in the sieve and end up in the bowl. The sieve is designed to allow smaller particles, like water, to pass through while blocking larger particles. So, the water will flow through the sieve and collect in the bowl below, while any solids or larger particles that were in the water will remain in the sieve.

If you hold a fine-grained sieve above a bowl and pour sand into the sieve while holding it still, the sand will be caught in the sieve and will not pass through the holes. This is because the holes in the sieve are too small for the sand particles to pass through.

So, after pouring the sand into the sieve, the sand will remain in the sieve, while any finer particles, like dust or small stones, will pass through the sieve and end up in the bowl below. If you want to get the sand into the bowl, you would need to shake or tap the sieve gently, allowing the sand to pass through the holes and collect in the bowl.

The small stones may pass through the sieve if they are smaller than the size of the holes in the sieve. However, if the stones are larger than the size of the holes, they will also be caught in the sieve like the sand.

The reason why smaller particles like dust or sand pass through the sieve more easily than larger particles is due to the size of the holes in the sieve. A fine-grained sieve has smaller holes than a coarse sieve, so only smaller particles can pass through. Sand particles are typically larger than dust particles, so they are more likely to be caught in the sieve. However, small stones may be smaller than the holes in the sieve, so they may pass through while the sand is caught.

The ability of particles to pass through a sieve is also dependent on the shape and size of the particles themselves. For example, if the sand particles are irregularly shaped or have sharp edges, they may be more likely to get caught in the sieve, even if they are smaller than the holes.

If you pour flour into a sieve held above a bowl, the flour will pass through the holes in the sieve and end up in the bowl. A sieve is designed to allow smaller particles, like flour, to pass through while blocking larger particles. So, the flour will flow through the sieve and collect in the bowl below, while any larger particles or lumps in the flour will remain in the sieve.

Using a sieve is a common technique in cooking and baking to remove any lumps or foreign particles from flour, which can help to ensure a smoother and more even consistency in the final product.

If the sieve is held completely still and not shaken, the flour may not pass through the sieve immediately. However, over time, gravity will cause some of the flour to fall through the holes in the sieve and collect in the bowl below.

The speed at which the flour passes through the sieve will depend on several factors, including the size of the holes in the sieve, the size and shape of the flour particles, and the amount of flour being sieved. If the flour is particularly fine and the holes in the sieve are large, the flour may pass through the sieve more quickly. However, if the flour is clumpy or contains larger particles, it may take longer for the flour to pass through the sieve, and some of the larger particles may not pass through at all.

To speed up the process and ensure that all the flour is sieved properly, it's recommended to gently shake or tap the sieve while holding it over the bowl. This helps to loosen any clumps and encourages the flour to pass through the sieve more quickly and evenly.