  # Equilibrium Q:     Can a body with only one force acting on it be in equilibrium? A:     No, the condition of equilibrium is Fnet = 0. Q:     Can a body in motion be in equilibrium? A:     Yes, the condition of equilibrium is Fnet = 0.  For an object in motion, Fnet = 0 means acceleration anet = 0 and velocity vnet = constant.  So, the only possible motion an object in equilibrium is the uniform motion (motion in straight line with constant speed.) Q:     How far must the Tower of Pisa lean before it topples? A:     The leaning Tower of Pisa is 55 meters high and 7.0 meters in diameter.  The top of the tower is 5.2 meters from the vertical (as of 1997).  The tower will topple when the center of mass is no longer above the structure's base.  If we treat the tower as a cylinder of uniform mass, its center of mass will be in the middle of the tower (where the line between the middle of the bases crosses the line that joins the middle of two opposite walls.   The center of mass will no longer be above the base when the top of the tower has moved 7.0 meters from the vertical (another 1.8 meters).  To find what angle this is calculate = sin-1 (7.0 m/ 55m) = 7.3°. You can learn more about the Tower of Pisa and the attempts to save it at this site: GF's Leaning Tower of Pisa Web Page

## References

### Equations

Static Equilibrium
 Balance of Forces Fext = 0 Balance of Forces in the xy Plane Fx = 0   and Fy = 0 Balance of Torques  ext = 0 Sum of Torques if the forces are balanced in the xy plane  z = 0

# Mechanics List of Topics

 Measurements Newton's Laws Potential Energy and Conservation of Energy Rotation of Rigid Bodies Elasticity Vectors Forces and Fields Linear Momentum Angular Momentum Mechanical Oscillations Motion of Point-Mass Objects in One Dimension The Gravitational Field Collisions Torque Mechanical Waves Motion of Point-Mass Objects in Two and Three Dimensions Kinetic Energy and Work Circular Motion of Point-Mass Objects Equilibrium Sound  ครั้งที่

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