Static Equilibrium: Forces and Torques

Topics: Torque, Force, Classical mechanics Pages: 9 (2066 words) Published: March 13, 2013






1) What is meant by static equilibrium?

The meaning of static equilibrium can be explored by first examining the definition of equilibrium. Equilibrium means that an object is at rest or that the objects center of mass moves at constant velocity relative to the observer.

Static equilibrium is the case where an object is at rest. An object is at rest or at static equilibrium when the net force applied on it is zero. When an object is at rest about an axis it may have a tendency to rotate depending on the distribution of mass or if a force is applied. This tendency to rotate is called torque must also be equal to zero for the conditions of static equilibrium to be satisfied.

2) How do you define torque (or moment of a force)? Give the most general definition, illustrate with a diagram.

Torque is the tendency of a force to rotate an object about an axis. Torque is defined as the product of the force applied perpendicularly to the surface of the affected object and the distance of that force from a point of pivot –

Torque = Force * Distance

Axis of rotation/Pivot

3) Can a body be in static equilibrium if subject to only one force? Explain briefly.

A body cannot be in static equilibrium if it is subject to only one force. When one force is applied the object will accelerate governed by the following equation:


If the object is in static equilibrium then it is also at rest and net forces acting on the object equal zero. This necessitates that there must be a counteracting force cancelling out the single original force that was applied to the object. Otherwise the object will not achieve static equilibrium.

4) Define center of gravity.

Associated with every object is a specially defined point called the center of gravity. It is a point where the mass is evenly distributed throughout the dimensions of the object. If the object is of uniform composition then the center of gravity will be in the geometric center of the object. However if the object is of an irregular shape the centre of mass may not have any specific position on the object and may lie outside the object body. For example a horseshoe. (Serway and Jewett, 2006)


The objective of this lab was to study the role of forces and torque that act on a certain object in the state of static equilibrium. This was achieved through a three part experiment. A rigid body – ruler, supported about stand at one end acted as the rotational axis. A force was applied at varying distances from the rotational axis using varying hanging weights.

Through this setup the center of gravity is to be determined of the rigid body. The objectives are to determine if the center of gravity is where it was expected, and to calculate the values of rotational torque applied at various lengths upon the rigid body. BACKGROUND:

Static equilibrium refers to an object that is not moving in any direction. It can be defined with the following equations:

1. The sum of all external forces acting on the object must be zero, in all directions.

2. The sum of all torques, which was calculated with respect to a common point, must be zero as well.

The measured tendency of an applied force to cause rotation is called torque. Torque is also referred to as the moment of force. This is a vector quantity, meaning direction matters, relative to the axis of rotation. Conceptually, if the torque of a force causes a clockwise rotation (CW) on the plane, it is negative. Vice versa holds true for when the torque is counter-clockwise (CCW).

Torque is represented by the...
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