Static Equilibrium Lab - University of Michigan
Instructor Outline: UM Physics Demo Lab 07/2013Static EquilibriumLab length: 80 minutesLab objective: To teach the concepts of vector addition, the net force/torque as the vector sum of multiple forces/torques, torque as vectors, right hand rule for torque vector directions, unit conversion, mechanical advantage and center of gravity.Materials8 sets of 3 spring scales (Ohaus 20N/2000g)8 2’ x 2’ perforated boards8 sets of 3 tool hooks for boards8 one inch diameter split rings8 sets of ten ? inch cut steel washers (of equal mass)24 Clear plastic rulers90 Xeroxed coordinate grid sheets8 yardsticks8 steel gussets (angle brackets)3 boxes sharp pencils**Demonstrations: 1A40.30 Magnetic Vectors 1D40.10 Dumbbell with Light 1J20.60 Wine Bottle Balance Introduction: 10 minutes-LectureThe concepts of tip-to tail vector addition and subtraction are introduced.Exploration stage: 30 minutes – Group lab-workThe students pull on the ring with three scales and hold the scales down with the tool hooks to hold the forces steady. A pre-printed coordinate grid is then slid under the ring and the force directions marked with a pencil and the force magnitudes recorded. The three force vectors are then represented as arrows with 1 cm corresponding to 1 N of force. The students then trace the vectors onto a second coordinate sheet and pictorially add the vectors tip to tail to get a result close to zeroAnalysis stage: 10 minutes – LectureThe results of the Exploration are discussed and the force condition for static equilibrium is stated.Exploration stage: 20 minutes – Group lab-workThe students now balance yardsticks with various weights at different distances and deduce that the product of the weight and distance must be equal to achieve balance.Analysis and summary stage: 10 minutes – LectureThe concept of torque as a vector and the right-hand rule (RHR) for assigning the vector direction are introduced. The condition for rotational equilibrium is then stated and discussed along with the mechanical advantage afforded by a long lever arm. The concepts of mechanical advantage and center of gravity are introduced and a final summary presented.Concepts developed:Vector addition and subtraction.Torque as a vector and the RHR for assigning force/net torque as the vector sum of individual forces/torques.Condition for linear and rotational static equilibrium.Mechanical advantage.Center of mass and center of gravity. ................
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