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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. forces on the block forces on the rope FT FN Frope -FT Ffr m m Fg Frope = -FT by the law of reaction**Tension or Normal Force**• Tension and normal forces are different. • A pull on an object - tension • A push from a surface - normal force • Either one or both may be present. Normal force Tension force FN FT Ffr m Fg**Coupled Motion**v2 v1= v2 FT2 FT2 FT1 m2 m1 Ffr2 Ffr1 • Objects linked by tension move together • Same velocity and acceleration • Tension may not be the same on two ropes • FT2 = Ffr2 • FT1 = Ffr1 + FT2 = Ffr1 + Ffr2**m1**m1 m1 m2 m2 m2 Pulley • A pulley uses tension to transfer a force to another direction. FT forces on the rope FT forces on block 1 forces on block 2 Ffr Frope Frope Fg**The normal force on m1 equals the force of gravity.**The force of gravity is the only force on m2. Both masses must accelerate together. m1 m2 Pulley Acceleration • Consider two masses linked by a pulley • m2 is pulled by gravity • m1 is pulled by tension • frictionless surface Ffr Frope**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/s2)/(3.2 + 2.2 kg) = 1.8 m/s2. • Using y = (1/2)at2, it will take t2 = 2(1.80 m)/(1.8 m/s2) • t = 1.4 s.**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