Many of the words we use in science have a somewhat different or restricted meaning when compared to their use in everyday conversation. For example, in casual conversation we may say that “gold is heavier than aluminum”, which of course is nonsense. How ‘heavy’ something is reflects the amount of mass present. A gram of gold weighs the same as a gram of aluminum. A gram is a gram is a gram.
What we mean is that gold is denser than aluminum. That is, a block of gold would be heavier than a block of aluminum of the very same size. In everyday life we use ‘heavy’ and ‘dense’ as though they mean the same thing.
But they don’t.
People shave with colloids, put colloids in their hair and on their sandwiches, and then have a cold colloid for desert. You may have topped your hot chocolate with a colloid or put a colloid in your cereal this morning. It seems that the world is full of colloids. But what are they?