The above design project demonstrates Issac Newton's 
First Law of Physics:

"An object at rest tends to stay at rest and an object 
in motion tends to stay in motion with the same speed 
and in the same direction unless acted upon by an 
unbalanced force."

This example demonstrates "Static Equilibrium".  It  
also explains the principle of the operation of a truss
in architecture.  A trussed roof or basement floor joist 
carries the load from the middle of the building to its
outside walls.

The Greek "sigma" letter (E) is the mathematical way of 
expressing "the sum of".  The illustration above shows
that the sum of the forces on the block are "zero".
Does this mean that there are no forces on the block?


No, it means that the forces are equal and opposite 
such that they zero each other out.  The belt can not
flip up out of the groove and fall to the floor and the
block can not fall down off the end of the pencil.


Where "F" equals force, "X" equals the horizontal
radius direction while "Y" equals the vertical radius
direction.

There are two requirements for the above project to
work as described.


1. The belt must weigh more than the Belt-Balancer
block to hold it.  Our block was made of Styrofoam.


2. The belt used is a leather belt with some natural 
spring memory, turned inside-up, such that the 
belt's material memory applies a force to the top 
groove edge of the block.