The A frame
Practical Action
X
AB
C
0.8m
String
Weight
4 metres
Poles
Figure 2: The A frame layout
A = 1st graduation mark
B = 2nd graduation mark
C =Approved frame centre = Centre of distance between A to B.
Construction procedure
• Nail together the top of the 3 metre poles so that there is an inverted V form. These
poles should be thin, at most 3 cm in diameter.
• Open the base of the V until its 4 metres.
• From the pivot of the V measure 2.2 metres going down and mark on 3 m sides or
0.8m from the bottom.
• Nail the 1.5m rail across the 2 legs on these marks.
• From the apex suspend a string at whose end there should be a stone or half brick
knotted on. This is called a bob.
• You may add an extra strength by putting 2 or 3 rounds of tying wire over the nail
positions.
• The A Frame is now complete.
Calibrating the a frame
• Stand the A Frame and mark the positions of both legs on uneven ground.
• Wait for the string and weight to pendulum and finally rest.
• Mark the position onto which the string is on the rail = A.
• Exchange the leg positions.
• Allow the string and weight to rest after swinging.
2