087 – Invisible center of gravity

Introduction to:

Center of mass, equilibrium of forces, stable equilibrium, mass distribution  

Material: 

• cardboard box / packing box / box (e.g. shoe box)   
• table / chair / elevated surface  
• piece of weight (approx. 3-4 times the weight of the cardboard box)  

Instructions:  

• First, show that the cardboard box will fall off the table if it is not supported at its center of mass. In order to do this, place one corner on the edge or corner of the table with a much larger part of the box hanging in the air. 
• Place a weight in one corner of the cardboard box.  
• Now place the weighted corner of the box on the table   

Observation:   

• The cardboard box falls down without the extra weight. 
• It stays in place even though it is protruding far with the weight.    

Tips:  

• For a magic trick, you can put in a false bottom.  
• If necessary, glue the weight in place to prevent it from slipping.