Center of Gravity
Douglas Community Academy
3200 S. Calumet
CHICAGO IL 60616
Third grade students will be able to find the center of gravity and to define force and gravity.
Assorted shapes made of cardboard, yarn, washers; push pins, and a cork bulletin board.
A knife, new pencil sharpened, potato, empty 2-liter soda bottle with cap, and two metal forks of equal size.
Ask the question what is force? A force is a push or pull. The teacher will put the definition on the board. See if you can find the center of gravity of an irregular shape.
1. Cut out the shape from a piece of cardboard.
2. Pin the shape to a bulletin board with yarn and attach a weight at the end of the yarn.
3. Draw a line behind the yarn, pin the shape at several different points and draw a line each
4. The point at which the lines cross is the center of gravity of your shape.
Can you balance the shape from this point on the eraser of a pencil?
Ask the question what is gravity? The teacher will put the definition on the board. Gravity is the force that pulls objects back toward the earth. Gravity is the pulling force between two objects due to their masses.
What happened? All things have a balance point, or a center of gravity, at which they are in perfect balance. The pencil with the potato is top heavy and will not balance. By adding forks to the potato, you change the center of gravity.
The students should be able to use specific vocabulary to define force and gravity.
Every weight has a center of gravity.
Taylor, Barbara; Weight and Balance, New York 1990