Chapter 5 Work and Machines

Chapter 5 – Work and Machines ICP Main Concepts & Vocabulary Vocabulary 1.Work; 2 joule; 3 Newton; 4 power; 5 Watt; 6 machine; 7 effort force; 8 resistance force; 9 ideal machine; 10 mechanical advantage; 11 efficiency; 12 ideal mechanical advantage (IMA); 13 simple machine; 14 lever; 15 pulley; 16 block and tackle 17 wheel and axle; 18 inclined plane; 19. Screw; 20 wedge; 21 compound machine

1. The transfer of energy occurring when a force makes an object move; W = F x d work = (force)(distance) 2. Unit of energy equal to kilogram (meter)2 / (second)2 ; J = kg m2 / s2 = Newton (meter) J = N. m 3. Unit of force equal to kilogram (meter) / (second)2 = kg m / s2 = N 4. The amount of work done or energy transferred in a certain unit of time; P=work /time = energy /time 5. Unit of power = W = work/ time = 1 joule/ second = 1 J/ s 6. A device that makes doing work easier, 1) increases amount of force being applied, 2) increases the amount of distance over which that force can be applied, or 3) changes the direction of the applied force

7. The force applied to the machine; is equal to Fe and contributes to the input work, Win 8. The force applied by the machine to overcome resistance; = Fr ; contributes to the output work, Wout 9. Perfect machine which loses no energy to heat, such that Win = Wout 10.The number of times a machine multiplies the effort force; symbol = MA = Fr /Fe 11.A measure of how much work put into the system that is changed into useful output

work by the machine; Efficiency = (Wout / Win ) x 100% ; in real life, this is always less than 100% due to heat loss 12.IMA, or the MA when there’s no loss of energy due to heat. IMA = length of effort arm/ length of resistance arm; IMA = radius of wheel/ radius of axle IMA = length of slope/ height of slope; IMA = effort distance/ resistance distance 13.A machine that does work with only one movement: lever, pulley, wheel & axle, inclined plane, screw, and wedge 14.A bar that is free to pivot or turn about a fixed point 15.A grooved wheel with a rope, chain, or cable running along the groove 16.A system of pulleys consisting of fixed and movable pulleys 17.A machine consisting of 2 wheels of different sizes that rotate together 18.A sloping surface, such as a ramp that reduces the amount of force required to do work 19.An inclined plane wrapped around in a spiral around a cylindrical post 20.An inclined plane with one or two sloping sides; it changes the direction of the effort force. 21.A machine in which 2 or more simple machines are used together, such as a can opener Main Concepts Work I. Transfer of energy that occurs when a force makes an object move.  W = Force x Distance = N. m = (kg m/s2)(m) = kg m2/ s2 = joules = J  Motion must be in the same direction as the applied force.  Distance is how far object moves while the force is being applied!  When you do work on an object, you increase its energy & decrease your own. Power I. The rate at which work is done, i.e., the amount of work done in a certain amount of time  Power = work / time; P = W/ t  Watts is unit for power; a watt is 1 J/ sec II. The energy transferred divided by the amount of time needed for the transfer to occur.  Power = energy / time; P = E/ t

Machines I. A device that makes doing work easier  Increases the force you can apply (bottle opener or a car jack)  Increases the distance over which the force is applied (ramp or a leaf rake)  Changes the direction of an applied force (window blinds, an axe, or a splitting maul) II. Effort & Resistance Forces

 Effort force = force applied to the machine = Fe = your pull on the hammer’s handle

 Resistance force = force applied by machine to overcome resistance = Fr = claw’s pull on nail III. Conserving energy  Energy is never created nor destroyed!

 Input work =Win = (Fe)(distance over which effort force is applied) = (Fe)(de)

 Output work = Wout = (Fr)(distance that the force moves the object) = (Fr)(dr)

 Wout = Win ONLY when there is NO energy changed to heat, which is IDEAL, but never occurs. IV. Mechanical Advantage  The number of times a machine multiplies the effort force is the mechanical advantage (MA)

 MA = Fr / Fe; MA = 1 when only the direction of the force has been changed V. Efficiency

 A measure of how much Win is changed into useful Wout by the machine

 Efficiency = (Wout / Win) x 100%  Can never be 100% efficient because friction causes a decrease in useful work Simple Machines  Do work with only one movement  Six types: lever – wheel & axle and pulley; inclined plane – screw and wedge o Lever = a bar that is free to pivot, or turn, about a fixed point (the fulcrum)

. effort arm = distance between fulcrum & place of applied Fe

. resistance arm = distance between & place of applied Fr  First-class lever

fulcrum is between the Fe and the Fr - (prying off a paint can lid) multiplies force & changes direction of force . Second-class lever

Fr is between the Fe and the fulcrum – (wheel barrow) multiplies force . Third-class lever

Fe is between the Fr and the fulcrum – (swinging bat hitting ball) increase the distance over which the resistance force is applied . Mechanical advantage of a lever o If ideal, IMA = (length of effort arm) / (length of resistance arm) o Pulleys = A grooved wheel with a rope, chain, or cable running along the groove A fixed pulley is a modified first-class lever with the axle acting like the fulcrum Movable pulleys have one end of the rope fixed & wheel is free to move. A block & tackle is a system of pulleys consisting of fixed & movable pulleys. Force is divided equally among various supporting rope segments. Number of pulleys, however, also increases friction to decrease the MA. o Wheel and Axle = machine consisting of 2 wheels of different sizes that rotate together

Usually the Fe is exerted on the larger wheel & the smaller wheel (axle) exerts

Fr Examples include doorknobs, faucet handles, and pencil sharpeners. Point where handle connects = fulcrum; length of handle = effort arm; radius of wheel = resistance arm, so it’s a modified lever

IMA = (radius of wheel) / (radius of axle) = r w / r a ; IMA increases as wheel radius does Gears are a modified form of the wheel & axle with the larger gear being the effort gear. Gears change the direction of the force. o Inclined Planes = a sloping surface that reduces the amount of force required to do work IMA = (effort distance) / (resistance distance) = (length of slope) / (height of slope) = l / h . Screw = inclined plane wrapped around a cylindrical post . Wedge = inclined plane with one or more sloping sides  Knife blade is an example; changes direction of the force Compound Machines  When > 2 simple machines are used together o Can opener: handles = lever; metal wheel = wedge; turning handle = wheel & axle o Car: internal combustion engine and multiple systems of gears