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Tension

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Tension Forces A taut rope has a force exerted on it. If the rope is lightweight and flexible the force is uniform over the entire length. This force is called tension and points along the rope. m forces on the block FNFN F fr F rope FgFg m forces on the rope FTFT -F T F rope = -F T by the law of reaction

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Tension or Normal Force Tension and normal forces are different. A pull on an object tensionA pull on an object tension A push from a surface normal forceA push from a surface normal force Either one or both may be present. m Normal force FNFN F fr FgFg Tension force FTFT

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Coupled Motion Objects linked by tension move together Same velocity and acceleration Tension may not be the same on two ropes F T2 = F fr2 F T1 = F fr1 + F T2 = F fr1 + F fr2 m2m2 F fr1 FT1FT1 FT2FT2 m1m1 F T2 F fr2 v 1 = v 2 v2v2

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Pulley A pulley uses tension to transfer a force to another direction. m1m1 m2m2 m1m1 m1m1 m2m2 m2m2 F rope F fr F rope FgFg FTFT FTFT forces on block 1forces on block 2 forces on the rope

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Pulley Acceleration The normal force on m 1 equals the force of gravity. The force of gravity is the only force on m 2. Both masses must accelerate together. m1m1 m2m2 F rope F fr Consider two masses linked by a pulley m 2 is pulled by gravitym 2 is pulled by gravity m 1 is pulled by tensionm 1 is pulled by tension frictionless surfacefrictionless surface

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Atwood’s Machine In an Atwood machine both masses are pulled by gravity, but the force is unequal. The heavy weight will move downward at (3.2 - 2.2 kg)(9.8 m/s 2 )/(3.2 + 2.2 kg) = 1.8 m/s 2.(3.2 - 2.2 kg)(9.8 m/s 2 )/(3.2 + 2.2 kg) = 1.8 m/s 2. Using y = (1/2)at 2, it will take t 2 = 2(1.80 m)/(1.8 m/s 2 ) t = 1.4 s.t = 1.4 s.

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Mechanical Advantage With more than one pulley the force needed to lift an object can be reduced. The pulley is a simple machine. The mechanical advantage to the left is 2. next

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Announcements CAPA Set #5 due today (Friday) at 10 pm CAPA Set #6 now available, due next Friday Next week in Section Lab 2: Acceleration due to gravity.

Announcements CAPA Set #5 due today (Friday) at 10 pm CAPA Set #6 now available, due next Friday Next week in Section Lab 2: Acceleration due to gravity.

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