Mechanics
> Statics of Rigid Bodies > Resolution of Forces
DCS#
1J30.xx
MODEL STONEHENGE
STONE RAISER
APPARATUS
A-frame apparatus
202-13-C
pulley clamp
202-01-D5
C clamp
202-01-E6
50 g weight hanger
101-05-D1
set of masses
101-05-D
DESCRIPTION
The counterweighted A-frame can be
used to rotate a 2x4 into an upright position, in the manner believed
to have been used to raise the stones at
Stonehenge.
Turn the crank to drag the blocks toward the end of the 2x4 until they
tip it into the pit. Connect the string on the 2x4 to the vertex
of the A-frame support, and another string from the cross-piece over
the pulley to the weight hanger. Add mass to the weight hanger to
pull the 2x4 into an upright position.
Compare this to the mass required if the 2x4 is pulled directly,
without the A-frame, and determine the mechanical advantage obtained by
using the A-frame.
NOTES
The height of the vertex
of the A-frame is 4x that of the cross-piece (51 cm vs 13 cm) which
is the height of the string for the unaided pull.