2A machine is a device that makes doing work easier. Machines increase the force applied to an object.Ways to make work easier:Increase forceIncrease distanceChanging direction
3Work Done By Machines Effort Force- force applied to a machine (FE ) Resistance Force-force applied by the machine to overcome resistance. (FR ) in Newtons NInput Work-work done by you on a machine (Win )Output Work-Work done by machine (Wout )Work output is always smaller than work input due to friction.
4Ideal machinesIf no friction was involved then Wout = Win
5Mechanical AdvantageNumber of times a machine multiplies the effort force.Calculated by:MA= Effort force / Resistance force
6EfficiencyMeasure of how much of the work put into a machine is changed into useful output work by the machine.
7Calculating Efficiency Efficiency = Work Output / Work Input x 100%
9Levers Three types of levers. A bar that is free to pivot, or turn about a fixed point.Effort Arm-distance from the fulcrum to where the effort force is applied.Three types of levers.
10First Class leverFulcrum located between the effort and resistance force.Used to multiply force.Changes direction of the force.
11Second Class LeverResistance force is located between the effort force and the fulcrum.Always multiply the force.
12Third Class leverEffort force is located between the resistance force and the fulcrum.Always increase distance over which the resistance force is applied.
13Mechanical Advantage of a Lever IMA-Ideal Mechanical AdvantageIMA= Length of the effort arm =LeLength of resistance arm Lr
141. What is the length of the resistance arm? 2. What is the length of the effort arm?3. What is MA of the see saw above?4. What is the resistance force in the diagram?5. How much effort force would be needed to overcome the resistance force?
15Answersmm3. 1 MA = 3.5 m / 3.5 mNN MA = resistance force/effort forceso 1 = 350 N / x1x = 350 N1 1x = 350 N
16PulleysA grooved wheel with a rope, chain, or cable running along the groove.A first class lever.Can multiply the resistance force and change direction of the force.
17Fixed Pulleys Attached to something that does not move. Only changes direction of the force. Effort force not multiplied, IMA is 1.
18Moveable PulleysOne end of the rope is fixed and wheel is free to move.Multiplies force.
19Mechanical Advantage of a Pulley System 1. MA = ______________2. MA = ______________3. MA = ______________
23Wheel and AxleA machine consisting of two wheels of different sizes that rotate together.IMA = Radius of the Wheel = ReRadius of the axle RaMechanical advantage of a wheel and axlemay be increased by making the radius of thewheel larger.
26Inclined PlaneA sloping surface that reduces the amount of force required to do work.IMA= effort distance___ = length of slope = IResistance distance Height of slope h
27Inclined Plane 1. What is the height of the inclined plane? What is the length of the inclined plane?3. What is the mechanical advantage of the inclined plane?4. How much effort force would be needed to push the dump truck up the mountain?
28Answers to MA of Inclined Planes 3. 30 MA = 3000 m / 100 m4. 30 N=MA = resistance force/effort forceso 30 = N / x30x = Nx = 500 N
29ScrewInclined plane wrapped in a spiral around a cylindrical post.
30Wedge An inclined plane with one or two sloping sides. Changes direction of the effort force.
31Compound MachinesTwo or more simple machines used together.
32Compound MachinesTwo or more machines linked so that the resistance force of one machine becomes the effort force of the second.The mechanical advantage of a compound machine is the product of the simple machines it is made up of.
33Answers to Work Problems 2 1) A. 250,000 J 3) A. 50 mB W B. 245 NC. 250,000 J C. 245 N2) A. 0 J D. 3.2 s (d=1/2 gt2)B. 22,968.8 J E s (V=gt)C. 64,312 J F. 12,250 JD JE m ) 5500 WF. 525 N (∑F=1/2 mv2 /d) 5) A N (set up as ratio)* B. 17,500N* C. 60%*