Prescribed practical 3 - The Principle of Moments - Section 1

A guide to carrying out an experiment to determine the Principle of Moments

Purpose

To plan and carry out experiments to verify the Principle of Moments using a suspended metre rule and attached weights.

The Principle of Moments states that when a body is balanced, the total clockwise moment about a point equals the total anticlockwise moment about the same point.

Equation

Moment =force F x perpendicular distance from the pivot d.

Moment = Fd

Apparatus

A uniform metre rule, retort stand, boss and clamp, two 100 g mass hangers and 12, 100g slotted masses, a g-clamp, three lengths of string.

A uniform metre rule, retort stand, boss and clamp, two 100 g mass hangers and 12, 100g slotted masses, a g-clamp, three lengths of string.

Method

  1. Suspend the metre rule at the 50 cm mark so that it is balanced horizontally. The ruler is said to be in equilibrium. The 50 cm mark is the pivot.
  2. Suspend a mass, m1, from one side of the ruler a distance, d1, from the pivot. Read the distance d1 in cm, from m1 to the pivot. Record in a suitable table. Record the value of mass m1 in kg in the table too.
  3. Suspend a second mass, m2, from the other side of the pivot. Carefully move this mass backwards and forwards until the ruler is once more balanced horizontally. Read the distance d2 in cm from the mass m2 to the pivot. Record d2 in cm, in the table, along with the mass m2 in kg.
  4. Repeat several times using different masses and distances.
  5. Calculate the turning forces, F1 and F2, using W = mg.
  6. Calculate the clockwise and anticlockwise moments.

Safety

Clamp the retort stand to the bench with the g-clamp to it doesn’t fall and hurt someone or fall on their feet.

Place an obstacle, such as a stool, to keep feet from beneath the metre rule, to make sure the mass hangers don’t fall on someone’s foot.

Safety glasses should be worn in case the meter rule swings and hits someone in the eye.

Results

For ANTICLOCKWISE moment:

Mass m1 in kgTurning force F1 in NPerpendicular distance from the pivot d1 in cmAnti- clockwise Moment in Ncm

For CLOCKWISE moment:

Mass m2 in kgTurning force F2 in NPerpendicular distance from the pivot d2 in cmClockwise Moment in Ncm