Name:
______________________________________________
Date of lab:
______________________
Section number:
M E 345._______
Lab 11
Precalculations –
Individual Portion
Mechanical Measurements Lab:
Measurement of Mechanical Quantities
Precalculations Score (for instructor or TA use only):
_____ /
20
1.
In the eddy current dynamometer setup, a clever device is used to directly
measure torque. As seen in the sketch to the right, mass
m
is attached to a
wheel of radius
R
, and is lifted up as torque
T
applied
is applied
(counterclockwise) to the wheel. Gravity provides a constant downward
force
W
mg
=
, but the moment arm (torque arm)
r
increases as the weight
moves up in elevation, causing an increase in the counteracting (clockwise)
torque
T
counteracting
. The wheel is stationary when
applied
counteracting
T
T
T
=
Weight,
W
R
r
θ
T
counteracting
T
applied
Mass,
m
=
,
which is read directly on the torque scale built into the instrument. Derive
an expression for torque
T
as a function of weight
W
, radius
R
, and angular
displacement
θ
, showing all your algebra for full credit.
2.
From the analysis above, does torque increase
linearly
or
nonlinearly
with angular displacement
θ
? Explain.
3.
The scale on the eddy current dynamometer torque gage reads torque in units of oz-in (force in ounces multiplied
by moment arm in inches). If the reading is 130. oz-in, what is the torque in Newton-meters? If the shaft rotation
rate is 1750 rpm, calculate the shaft power in watts. For full credit, show all your work, including unit
conversions for both calculations.
Note
: Save your equations, because you will need them to do this lab
.

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