The conditional 0 is used to express general truths and facts (often things based on scientific fact).
Uses the simple present tense:-
|If you heat water to 100°C,||it boils.|
|Water boils||if you heat it to 100°C,|
- If you drop an apple, it falls. = An apple falls, if you drop it. (This is an absolute truth based on scientific fact - gravity).
- If you don't do your homework, I will be disappointed. = I will be disappointed, if you don't do your homework. (This is a general truth based on previous knowledge - you know that I am disappointed if people don't do their homework).
Note! Most zero conditional sentences mean the same thing if "when" is used instead of "if".