Mathematics/Physics
Center
of Gravity
Wanda Pitts 
Douglas
Community Academy 
3200 S.
Calumet 

CHICAGO IL
60616 


(773) 5349263 
Objective(s):
Third
grade students will be able to find the center of gravity and to define
force
and gravity.
Materials:
Assorted
shapes made of cardboard, yarn, washers; push pins, and a cork bulletin
board.
A
knife, new pencil sharpened, potato, empty 2liter soda bottle with
cap, and
two metal forks of equal size.
Strategy:
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
Time.
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.
Performance
Assessment:
The
students should be able to use specific vocabulary to define force and
gravity.
Conclusions:
Every weight has a center of gravity.
References:
Taylor,
Barbara; Weight and Balance, New York 1990