Presentation on theme: "Tension. 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."— Presentation transcript:
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
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
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
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
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
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.
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