Friday, November 30, 2012

Thanksgiving Balloons

By Mike Jones

After watching the Macy’s Thanksgiving Day parade I started thinking about the relative physics involved with keeping balloons from flying away.  I noticed that each balloon has many strings held down by many bodies, and was curious as to the approximate force needed by each individual to keep the balloon from flying away.
 
I found this video and used the volume of this new balloon (14,000 ft^3= 396.44m^3) (http://www.sciencefriday.com/video/11/17/2011/meet-the-balloonatics.html).  I approximated 30 strings coming off the balloon, ρair=1.2041kg/m^3, and ρHe=0.1786kg/m^3.  Solving for the buoyant force:
FB=ρVg=(ρair - ρHe)Vg= (1.2041kg/m^3 - 0.1786kg/m^3)( 396.44m^3)(9.8m/s^2)
FB= 3,984.18N or approximately 4,000 N.
Assuming the buoyant force is equally distributed over the 30 attached strings then the approximate force each person exerts on each string is 4,000 N/30= approximately 133 N per string. 

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