Author:  Kathy Weil		
Subject:  Science
Topic:  Gravity
Grade Level: elementary 
Student Level:  all

Teacher Presentation:  yes
Student Activities:  yes
Materials Needed:  see below
Directions:
Objects have weight because gravity pulls on them.  The greater the pull of gravity on an object, the more it weighs.
People do not feel their weight if there is no gravity pulling on them or if they are floating freely.  When you bounce on a trampoline you feel weightless when you are in the air, but the feeling will last only until you come down to Earth again.
The pull of the Earth's gravity gets less farther out in space, so things weigh less in space.  Astronauts float about in their spacecraft because there is little gravity to pull them down.
Gravity on the moon is about 1/6th the gravity on Earth, so a space suit that weighs 183 pounds on Earth only weighs about 31 pounds on the moon.  This makes it much easier for astronauts to move around on the moon; they can even hop like kangaroos.
Experiment:  Make a Spring Balance
This spring balance will help you to compare the weight of small objects.
Needs:  a yogurt cup, thin string, paper clips, thumbtack, paper, ruler, pencils, rubber band
1.  Press the thumbtack into a vertical surface from which you can hang the balance.
2.  Loop the rubber band inside the paper clip and hang the paper clip from the thumbtack.
3.  Make three holes in the rim of the yogurt cup and thread the string through them to make a handle.  Tie the ends together and then tie them to the end of the rubber band.
4.  Make a scale for your balance, using a piece of paper fixed behind the rubber band.  Mark the point at the end of the rubber band before you weigh something, then mark how far down this point comes when you have something in the cup.
5.  Compare the weight of small objects such as a pencil, a marble, a stone, a handkerchief, or a grape.