Topics: Force, Torque, Energy Pages: 5 (1223 words) Published: October 5, 2010
Experiment 6: Conditions for Equilibrium
Laboratory Report

Kristine Bautista, Kevin Benin, Raisha Buan, Gabrielle Bugna

Depertment of Math and Physics
College of Science, University of Santo Tomas
Espana, Manila Philippines


The aim of this experiment is to determine the conditions of equilibrium, to locate the centre of gravity, and to demonstrate rotational equilibrium. The experiment was performed by doing a series of activities such as the use of a force table, strings, and a force board. Results were obtained theoretically and experimentally.


Equilibrium is the state of an object when no part of the object is accelerating. there are two common types of equilibrium: static equilibrium and neutral equilibrium. Equilibrium usually is related to potential energy, for a system to be at equilibrium it must maintain the balance between the two types of mechanical energy: potential and kinetic. The first equilibrium: static means that the system is in a relatively low (relatively means that there could be lower energy but the current states is a local minimum), thus small disturbances to the system will be returned to its original equilibrium. The other type of equilibrium is neutral equilibrium, the relative energies of the system is constant, thus disturbances to the system will move the system but it will remain at the same equilibrium value, and the system makes no effort to return to its original state.2 Equilibrium is composed of

two conditions (1) Net force is equal to zero and (2) Net torque is equal to zero.

Torque is a measure of how much force acting on an object causes that object to rotate. The object rotates about an axis, which we will call the pivot point. The distance from the pivot point to the point where the force acts is called the moment arm. Torque is simply the product of force and the moment arm.

The objectives of this experiment is to be able to determine the conditions of equilibrium, to locate the centre of gravity, and to demonstrate rotational equilibrium.


The materials used were a force table and its accessories, force board, cylinder of unknown weight, spring scale, electronic gram balance, card board, aluminium bar, unknown weight, and a protractor.

A. Equilibrant Force

The three pans of the force table were weighed and was labelled A, B, and C, respectively. Pan A was hanged at a 30o angle and pan B at 200o on the force table. 100g was placed on pan A and 150g on pan B and tension was recorded. The two tensions were balanced by placing weight on the pan C and by adjusting its angle in the force table. The tensions are balanced if the pin is exactly at the centre of the ring. The magnitude and position of the equilibrant was recorded. The theoretical equilibrant of the two tensions was solved by the component method and the percent error was computed.

Fig.1.Force table set-up

B. First Condition for Equilibrium

Using a force board, a cylinder of unknown weight was suspended by means of two strings. A spring scale was attached to one of the strings and was pulled horizontally until the pin on the force board is exactly at the middle of the ring. The reading on the spring scale was recorded as T1. The angles of the other strings were measured and a free body diagram was drawn. T2 was solved as well as the weight of the cylinder. The percent error was then computed.

C. Locating the Centre of Gravity

A circle with a diameter of 10 cm and a square with a side of 10 cm were cut from a card board and were weighed. The centre of gravity was determined by balancing the two figures.

D. Second Condition for Equilibrium

The centre of gravity of the aluminium bar was located by balancing it on a pencil. The cylinder from the previous activity was used and was then hanged 5.0 cm from one end of the bar. Using the force board, the aluminium bar was...

References: [1] Freedman, Roger A. et. al., University Physics, 12th ed., Pearson Education, Inc. Singapore, 2008.
[2] Tippens, Paul E., Physics, 7th ed., McGraw-Hill, Inc. New York, 2008.
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