If you have eaten a sweet called an 'acid drop' just think back to how it tasted. The sharp or sour taste was due to the acid in the sweet.

Vinegar also contains an acid, and this, too, gives the liquid its sour taste. Lemons also contain acid.

There are many kinds of acid. Some are weak and can be used in cooking and making food. Vinegar and lemon are like this. Others are much stronger and must be treated with great care. They are used in factories to make many different products. They are also used in batteries such as car batteries because acids conduct electricity.