filter

Everyday

1. A filter is a material or device with tiny holes that lets liquid or air pass but catches solid bits. tree →
2. To filter is to pass something through a filter to clean or separate it. tree →
3. A filter is a setting that changes or blocks something, like a photo filter or an internet filter. tree →
4. To filter in or out is to move slowly in small amounts, like light or people. tree →

In the lessons

In science, filtering separates an insoluble solid (like sand) from a liquid (like water) using filter paper and a funnel; dissolved salt passes through. Water treatment plants filter water to make it safe. Coffee machines, fish tanks and vacuum cleaners have filters. In online safety, filters block harmful websites. Phrases: filter paper, water filter, air filter, filter out, sunlight filtered through.

Examples

• We filtered the muddy water through filter paper. tree →
• The sand stayed in the filter. tree →
• Salt passes through a filter because it is dissolved. tree →
• Our fish tank has a filter to keep it clean. tree →
• Sunlight filtered through the leaves. tree →
• The school internet has a filter. tree →
• She added a funny filter to the photo. tree →

Note

A filter cannot remove dissolved things like salt or sugar; for that you evaporate the water. Filtered water from a stream may still have germs; it is not always safe to drink. Do not confuse filter with sieve: a sieve has bigger holes.