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BALANCING METER STICK

 

INTRODUCTION

The center of balance or center of gravity of an object is the point in that object at which you can consider all of its mass to be concentrated.  This point is also called the balancing point because the object will balance when supported at that point.  Tik Liem describes a process for determining the center of balance of complex objects,1 but this activity involves an even simpler process for finding the center of balance.  It is useful for grades 2-6.    
 

PURPOSE

The purpose of this activity is to find the center of balance or center of gravity of a uniform object, but the method can also be applied to more complex objects.
 

MATERIALS

1  or more Meter sticks

 

PROCEDURE

  1. Hold flattened hands out in front of you horizontally with palms facing toward each other.  This will result in the top inside edge of your index fingers being horizontal and facing upward, with your thumbs covering less than half the space along the top edge of your index fingers.

  2. Spread your hands nearly 1 meter apart, and have another person place the flat edge of a meter stick on your index fingers, with numbers on the centimeter side facing upward and toward you so that you can read them.

  3. Keep your hands flat in the vertical direction.  Bring your hands together slowly, making no moves affecting the meter stick except to let it slide along your index fingers.  Keep your hands level, and don't let the meter stick fall off your index fingers.

  4. Continue this process until the palms of your hands are finally touching.  Read the centimeter number between your palms.  That number should indicate the center of balance.

 

EXPLANATION

 

In the case of the meter stick above, the 50-cm mark appears between your palms.  That is the center of balance for the meter stick, half way between 0 cm and 100 cm for a uniform meter stick.   This occurs because the meter stick will fall off your index fingers if it becomes very far out of balance.  Similar behavior occurs for any uniform and regular object such as a 3" x 5" card or a book, and the center of balance is found to be half way from the exterior edges in all directions.


 

ADDITIONAL SUGGESTIONS

  

Repeat the above procedure with non-uniform and irregular objects such as a shovel or a rake.  The center of balance is found in the same fashion, but the process may be much more difficult for sufficiently non-uniform objects.  One end of the object is heavier than the other end, and the center of balance does not coincide with the center of the object.  Check your result with your teacher, your parent(s), or some other adult partner.
 

REFERENCES

  1. Tik L. Liem, Invitations to Science Inquiry - Supplement to First and Second Edition, Science Inquiry Enterprises, 14358 Village View Lane, Chino Hills, CA 91709, 1991, ISBN: 1-878106-01-5, p. 99.

 

Kids Involved Doing Science is at http://www.kids.union.edu     Modified 02/04/03 by C. & P. Scaife