What is centre of gravity?

What is centre of gravity?

Materials needed

• Meter stick (or yardstick)
• String
• Chair
• Various books

Procedure

1. Balance the meter stick on the back of the chair. It will balance at its "centre of gravity," which should e at or very near the 50-cm (18-in) mark. The part of the chair where the meter stick rests is the fulcrum.
2. Get two identical books and tie a string around each one.
3. Make a loop in the other end of each string and slide the loops over opposite ends of the meter stick. Leaving the books supported at the ends of the meter stick, where is the centre of gravity (where the fulcrum has to be to balance the books)?
4. Replace one of the books with a smaller book. With the books still suspended at the ends of the meter stick, where is the centre of gravity?
5. Replace the other book with a larger one. Where is the centre of gravity now?
6. What can you say about the centre of gravity when a large object is balanced with a small object? Consider the teeter-totter as you explain your answer.

For problem solvers: 

do you know what a mobile is? Build one? then explain why it is important to know about centre of gravity when constructing mobiles? If you do not know what a mobile is, ask your teacher, a parent, or a friend to help you get started.