Did you ever wonder what things are made of? Some objects are hard. Some are soft. Some things you can pour. The reason materials are different is because they are made of different bits called molecules. Molecules are so tiny that you cannot see them. Molecules are made of even tinier things called atoms. Two or more atoms link together to make a molecule. You and all things around you are made of molecules and atoms.
WHAT KINDS OF MOLECULES ARE THERE?
There are millions of different kinds of molecules. Some molecules are made of only one kind of atom. A molecule of oxygen gas is made of two oxygen atoms. Oxygen is a gas in air that all animals must breathe in order to live.
Your alarm clock goes off with a loud ring or buzz. You sing to yourself in the shower. You listen to your favorite music as you get dressed. You hear the wail of a siren on the way to school. You talk to some friends before class begins. You live in a world filled with sounds.
All of these sounds seem to be so different. Yet all sounds share one thing—vibrations. All sounds come from something that vibrates. If you bang on a drum, the top of the drum vibrates. When you talk, the vocal chords in your throat vibrate.
People say that time flies. They ask where the time went. They say that time marches on. You look at a clock or your watch to tell time. Do you ever wonder what time is?
Time isn’t something you can see or touch. You can only tell that time passes because other things change. Change, such as how tall you are, tells you that there is a past, present, and future.
WHAT IS PAST, PRESENT, AND FUTURE?
Time that is past happened already. You know when your summer vacation is over. The time of last summer’s vacation is past.