The force exerted by the propeller is quite small, but it can be measured
directly. You should use a variety of measurement tools, like the Thruster,
a hanging mass, or a force probe. You could build a force multiplier to
amplify the small force produced by the propeller.
Make multiple measurements and calculate the average. Compare your various
force measurements and decide which are most accurate. What is your best
estimate of the propeller force? What is the range of uncertainty in this
estimate?
Force Multiplier Sometime you want to measure forces which are either too large or too
small for your instruments. Forces can be multiplied (or divided) using a
lever. A Force Multiplier, to use with the Thruster, can be constructed
from cardboard. These are plans for a 4 to 1 multiplier, but these plans
could be changed to produce a different ratio.
Force Multiplier Parts
Figure E1
Parts
Figure E2
Multiplier with balanced forces
The force multiplier is a double-thick lever inside a sandwich. The top
and bottom of the sandwich are held apart by triple-layered spacer blocks
on each side of the lever. The lever pivots on a pop-rivet bearing. Forces
are applied at the holes in the ends of the lever, perpendicular to the lever.
