Experiment Five

A Brick on a string

Materials needed

Brick
string
A strong hook that the brick can be hung from.  
A handle  a 6 inch length of 3/4 dowel will do.

The important point here is that the string needs to be broken.   Even a double strand of the string needs to be broken.  You will need some string or strong thread that is not too strong.   For the pictures here yarn was used and works well.

The dowel is used so a double length of string can be used and the force is distributed evenly between the two strands.  

The first thing to do is to hang the dowel from the hook and be sure you can apply enough force to break the string.    Also repeat this with a double length of string and convince yourself that twice as much force is needed to break the string.    

To do the experiment hang the brick from the hook by one strand of string.    Now use a double strand to connect the brick to the dowel.    It should be obvious that if a force is applied to the dowel the single string will be the one to break.    In fact if an inceasing force is applied the single string will be the one to break.  The interesting part is when the dowel is given a strong quick pull.   This will cause the double string to break.   Surprisingly the brick will resist the force and the double string will be the one to break.    Of course be sure nothing will be damaged by the falling brick.   Including feet.

 As an demenstration it is possible to ask an audience which string they wish to see broken,  then apply either a slow force or a quick jerk to break either the top or bottom string.  

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