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Moments couples levers

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Published on July 8, 2013

Author: kwarne

Source: slideshare.net

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PowerPoint to teach moments, couples & levers
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Moments, Levers & Couples K WARNE

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Moments and levers  Definition  Principle of moments  Couples  Calculations  Classes  Mechanical advantage

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Moment of Force  The moment of a force about a point is the PRODUCT of the magnitude of the force and the perpendicular distance from the point to the line of the force. MOMENT = FORCE X DISTANCE = 5 x 0.25 = 1.25 N.m 5 N25 cm

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Calculate the moment of the force, or ……….., due to each force when several forces act on the same object using the equation:  = F … r F Calculating Torque F1 F2  = F x r = (F1x …1) + (F2x …2) When calculating torque the ………….of all the PERPENDICULAR FORCES must be used. TORQUE

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Equilibrium  For an object to be in equilibrium BOTH the sum of the …………….. acting on the object and the sum of the …………….of the forces must be ZERO.  Solve problems involving objects in equilibrium. F2 F3F1 FORCES (Linear) in equilibrium .: F1 + F2 + F 3 = …… MOMENTS in equilibrium .: ……………. a fulcrum. (F1) (F1….) + (F2…..) + (F3……) = 0 x1 x2 If a 60 Kg person stands 2 meters from one end of a 3 meter scaffolding plank what force is needed to support each end of the plank?

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Equilibrium Question F2 (F1. x1) + (F2. x2) + (F3.0) = 0 (F1.1)+((60x10)x2) + (F3x0) = 0 F1 + (1200) + 0 = 0 F1 = -1200 N .: F1 = 1200 N anticlockwise! A 1200 N force is needed at F1 to balance the plank! x1 x2 If a 60 Kg person stands on one end of a 3 meter scaffolding plank what force is needed to support him on the other end of the plank if the plank is balancing on a fulcrum 2m away from the 60kg person? ?? 60kg 2m F3 1 m F1 ?? Sum of all moments = zero Choose clockwise as POSITIVE! F3 = fulcrum

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Levers • Describe the terms “load” and “effort” for a lever • Define “mechanical advantage” as the ratio of “load/effort” and calculate the mechanical advantage for simple levers ………….................. …… ...... .. If in equilibrium: …… x ….. = …… x …..

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Levers • Describe the terms “load” and “effort” for a lever • Define “mechanical advantage” as the ratio of “load/effort” and calculate the mechanical advantage for simple levers LoadEffort e l If in equilibrium: E x e = L x l Mechanical Advantage Load Force Effort Force F E OR = e l == Effort distance Load distance =

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Mechanical Advantage  Mechanical Advantage is the RATIO of the LOAD to the EFFORT. Apply the concept of mechanical advantage to everyday situations. Mechanical Advantage Load Force Effort Force N Load L Effort E l e F E OR = e l == Effort distance Load distance =

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Types of Levers Class 1Effort Load Class 2 Effort Load Class 3 Effort Load Load Load Effort Effort o.75 o.25 o.75 o.75 o.25 o.25 Type 1 F in middle MA = e/l= 0.75/0.25 = 3 Type 2 F at end L in middle M.A. = e/l = 1/0.25 = 4 Type 3 F in mid L at end M.A. = e/l = 0.25/0.75 = 0.3 The weight of the lever helps in type 1 but not T2!

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Examples of Levers

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Force Couple A special case of moments is a couple. A couple consists of two parallel forces that are equal in magnitude, opposite in direction and do not act in a straight line but are separated by a distance (d). It does not produce any translation, only rotation. The resultant force of a couple is zero. BUT, the resultant of a couple is not zero; it is a pure moment. Example: A steering wheel of diameter 0.75 m is turned by a force of 20 N applied to each end. Calculate the magnitude of the force couple: Couple = F x d = (20 x 0.75) = 15 N.m F F d d 2 d 2 Couple = Total Turning Moment = (F x d/2) + (F x d/2) = ½ (F x d) + ½ (F x d) = F x d

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe Hi - This is a SAMPLE presentation only. My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as other resources, are freely available on my resource sharing website: www.sciencecafe.org.za (paste into your browser if link above does not work) Have a look and enjoy! Keith Warne

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