Now consider sand stirred into a jar of water. Ivan can see the sand grains in the water.

A sieve's holes are too big here: the sand would fall through with the water.

Ivan folds a piece of paper into a cone. The paper has holes too small to see.

Paper like this is called a filter.

He pours the mixture into the filter, and the water goes through the tiny holes, drop by drop.

Every piece of sand is too big for the holes, so the sand stays on the filter.

The filter from the side: the water drips through the paper into the cup, and the sand stays on the paper.

A paper filter in a funnel, with wet sand in it and clear water dripping into the jar.

A filter is a sieve with holes too small to see, so any piece you can see stays on it.

So a sieve is the tool for pieces big enough to sit on its holes.

Tiny bits in water would fall through a sieve, so a filter is the tool for them.

Three mixtures, the difference you can see in each, and the tool that uses it.