Science is dynamic. Not everything you learned growing up is 'true' today.
Clear liquids aren't always water.
Hydrochloric acid is clear. You wouldn't want to drink it.
You need oxygen to live.
Just as not all clear liquids are water, not all gases contain oxygen. Plus, you can diminish the amount of oxygen when you introduce other gases (e.g., carbon monoxide and carbon dioxide from combustion, helium from a balloon). Keeping this little scientific tidbit in mind may someday save your life.
Hot air rises.
So... if you can only heat the first or second floor of your house, heat the first floor.
What goes up must come down.
Gravity. Don't set heavy objects where they can fall on your foot, etc.
Water flows to the lowest point.
It's gravity in action. All liquids flow 'down'. This is handy to know if you ever need to actually find water, but its more practical applications involve plumbing and drainage.
Most materials expand when heated and contract when cooled.
Notable exceptions are water (ice floats, also important) and some types of wax. You can use this information to help open glass jars with metal lids, among other things.
That which doesn't kill you does not necessarily make you stronger.
I'm sure leaded paint chips taste nice and sweet. They won't kill you outright, but they aren't good for you. If you don't die immediately from something, that doesn't mean it's non-toxic.
While pure water doesn't conduct electricity, normal water does.
Hence it's a bad plan to have electric appliances where they can fall into the tub. It's not a great idea to go to the beach during a thunderstorm.