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Mechanical_lab - Name Date of lab Section number M E 345...

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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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