2 The Simple Machines Screw Wedge Inclined Plane Pulley Wheel and Axle Lever
3 MACHINES: A machine is a device that overcomes a large resistive force at a given point by applying a small force in convenient direction at a convenient point.It works as a force multiplier.It allows applying the force at convenient point.It allows applying the force in convenient direction.It is used to get the task achieved in less time.
4 Some technical terms:Mechanical Advantage: it is a ratio of load to the effort.M.A.= LOAD (L)EFFORT (E)Where,Load is the resistive force exerted by the object on which work is to be done.Effort is the force applied on the machine to overcome the load in order to get the work done.M.A > 1 for a good machineIt is a unit less quantity.
5 Some technical terms:VELOCITY RATIO: It is a ratio of velocity of effort to the velocity of the load.Where, VELOCITY OF EFFORT = d(e) / t andVELOCITY OF LOAD = d(l) / tTherefore, we haveVELOCITY RATIO = d(e) / d(l) ;Where d(e) and d(l) are the distances moved by the effort and load in time t.Hence, velocity ratio can also be defined as the ratio of distance moved by the effort to distance moved by the load.
6 SOME TECHNICAL TERMS:EFFICIENCY OF A MACHINE: It is defined as the ration of work output to the work input.Efficiency η = work output = WOUT / WINwork inputwork input is the work done on the machine by the effort.Work output is the work done by the machine on the load.It is a unit less quantity.
7 PRINCIPLE OF A MACHINEAccording to law of conservation of energy, work output cannot be more than work input.WIN = E × d(e)WOUT = L × d(l)Therefore,η = L × d (l) = L/E = M.A.E × d(e) d(e)/ d(l) V.R.M.A. = V.R × ηNote: In practice, due to friction M.A. < V.R.So efficiency is always less than 1Efficiency η = work output = WOUT / WINwork input
8 LEVERS:It is a rigid, straight or bent bar which is capable of turning about a fixed axis.It has four componentsRigid straight or bent barLoadEffortFulcrum
9 LEVERS: It works on the principle of moments Effort × effort arm = Load × load armLoad = Effort armEffort load armBut , M.A. = load / effortTherefore,M.A. = Effort arm Law of LeversLoad arm
11 First Class LeverFulcrum is between effort and load Effort moves farther than Resistance. Multiplies effort and changes its direction. The mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum.
12 First Class Lever.Common examples of first-class levers include crowbars, scissors, pliers, tin snips and seesaws.
13 Second Class Leverload is between fulcrum and Effort. Effort moves farther than Resistance. Multiplies EFfort, but does not change its direction The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance from the resistance force to the fulcrum.
14 Second Class LeverExamples of second-class levers include nut crackers, wheel barrows, doors, and bottle openers.
15 Third Class LeverEF is between fulcrum and RF (load) Does not multiply force Resistance moves farther than Effort. Multiplies the distance, the effort . The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance of the resistance force to the fulcrum
18 INCLINED PLACE:It is a sloping surface that works as a simple machine.An inclined plane is a flat surface that is higher on one end.Inclined planes make the work of moving things easier.
19 Inclined Planes M.A. = Load / Effort M.A. = l/h = W / W sin A= 1/ sin ATherefore from the geometry of the figureWe have as follows,M.A. = l/hl = slant height of inclined planeh = height of the inclined planeV.R. = d(e) /d(l)V.R. = l/hHence efficiency η = M.A. / V.R.= 1A sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed. You can use this machine to move an object to a lower or higher place. Inclined planes make the work of moving things easier. You would need less energy and force to move objects with an inclined plane.
20 Pulleys Pulley are wheels and axles with a groove around the outside A pulley needs a rope, chain or belt around the groove to make it do work
21 A SINGLE FIXED PULLEY :It’s mechanical advantage is unity, it means equal amount of effort is needed to lift any load.It’s used as it changes the direction of the effort
22 A single movable pulley: A movable pulley rotates freely about the axis that itself changes its position.Here the M.A. Is 2.V.R. Is 2 hence the effeciency becomes 1.
23 A single movable pulley A disadvantage here is that the effort which is to be applied is in upward direction which may not be convienent.To solve this we can attach one fixed pully without changing the M.A.This arrangement is called Block and Tackle system.
24 COMBINATION OF PULLEY: The upper part of the system consists a fixed pulley and the lower part consists of movable pulleys.The no. of movable pulleys are equal or one less than the number of fixed pulleys.
25 GEARSGears are toothed wheels which interlock to form simple machines.The tighter the joint, the less chance of slippingGears range in size but the important number is how many teeth a gear has.
26 PURPOSE OF GEARSIt is used to increase or decrease the turning effect of a machine.It means that if driving gear is rotated certain number of rotations per second the driven gear as desired can be rotated at more or less number of rotations per second.
27 V.R. OF GEARV.R. = No. of rotations per second of the driving gear ( n A )No. of rotations per second of the driven gear ( nB )nA is inversly proportional to RA , similarly for nB and RB .therefore we have, nA = RB = V.R.nB RAAlso RB = NB ; Where N are no. of tooth in respective gears A and BRA NA
28 More about gearsAutomobiles have four gears, and their size keeps of decreasing from first to fourth.During the first gear application , it produces low speed but largest torque.And as we increase the no. of gears the speed keeps on increasing.