Lever

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Is lifted upwards. upwardsSimple machines help us to do our work showing one ormore properties mentioned above.Types of simple machine effort is applied downwardsSimple machines have been divided into the following Fig 3.3 Pulley changes direction of forcesix types: Wheel and axle 1. Lever 2. Pulley 3. Wedge4. Inclined plane 5. Screw 6.1. Lever effortA lever is a rigid bar, straight or bent, which is able torotate about a fixed point called a fulcrum or pivot.The distance between the fulcrum and the loadis called load distance and the distance between load Edthe fulcrum and the effort is called effort distance.Only lever can show all the properties of a simplemachine among its types. Ld fulcrumOn the basis of the location of the effort, the load Fig 3.4 a lever lifting stoneand the fulcrum, levers are classified into threetypes: first class lever, second class lever and third class lever.a. First class lever E Ld EdThe lever in which the fulcrum is situated at anypoint between the load and the effort is called the Ffirst class lever. This type of lever shows all the Fig 3.5 first class leverproperties of simple machines. They change thedirection of force, multiply force and acceleratethe rate of doing work.When the fulcrum is close to the load, the effort distance increases and it multipliesforce. When the fulcrum is close to the effort, the load distance increases i.e. work isaccelerated. Crowbar, see-saw, dhiki, pliers, scissors and tinsnips are some examplesof this kind of lever. L EE FE L F

Above.b. A spanner is an example of: i. screw ii. wheel and axle iii. pulley iv. wedgec. Velocity ratio of a lever is calculated by using the formula: i. VR = Ld/Ed ii. VR = Ed × Ld iii. VR = Ed/Ld iv. VR = Ed × Ld/2d. A third class lever makes our work easy by: i. magnifying force. ii. gaining speed. iii. changing the direction of force. iv. (i) and (ii) both. SImple Machine 45e. A physical balance is based on the principle:i. E × Ld = Ed × L ii. E × Ed = L × Ldiii. Ed × Ld = E × L iv. MA × E = MA × Lf. The lever which makes our work easier only by accelerating the rate of work is:i. third class lever. ii. second class lever.iii. first class lever having effort distance equal to load distance.iv. first class lever having more effort distance.3. Differentiate between:a. mechanical advantage and velocity ratio b. velocity ratio and efficiency c. second class lever and third class lever d. fixed and movable pulley4. Give reason.a. Value of MA is always lesser than VR.b. Efficiency of a lever is never 100% or more.c. A tight knot can be easily opened by using a long spanner.d. The handles of tin-snips (metal cutter) are made long.e. Output work is always less than input work.f. The value of MA in the third class lever is always less than one.g. A second class lever needs less effort to lift

87. A lever is a rigid bar, either straight or bent, which is able to rotate about a fixed point, called a fulcrum.8. Fulcrum is in the middle of the first class lever; load is in the middle of the second class lever and effort is in the middle of the third class lever. THINGS TO DO wooden strip Make your own lever model. 1m1. Take a 1 m long wooden strip with equal thickness. F2. Mark at each 5 cm at the central line of the strip and first class levermake holes at each mark to pass wire in it freely. bending L E of wire E3. Bend three thick wires as shown in the diagram. F4. By using them, study the amount of effortrequired to lift a load changing its location in the Lfirst class lever. second class lever5. Study about the second class lever and the third FEclass lever also by using your own lever. third class lever L TEST YOURSELF1. Fill in the blanks.a. Nail-cutter is an example of the ........................... class lever.b. Mechanical advantage is calculated by the formula ....................... .c. Efficiency of a machine is never ............................ %.d. ................................. = Effort distance Load distanced e. ............................... is denoted by Eta (η).2. Tick ( ) the correct answer (MCQs).a. The value of MA is always less than VR because: i. effort decreases due to friction. ii. load increases due to friction. iii. some of the effort is wasted due to friction. iv. all of the

LF E (c) scissors (b) crowbarFig 3.6 (a) see-saw38 Modern Graded Science and Environment Book 8b. Second class lever LEThe lever in which the load is situated at anypoint between the effort and the fulcrum is Ldcalled the second class lever. This class of Ed Fig. 3.7 second class leverliver cannot change the direction of force. It is Fnot able to accelerate work because the loaddistance is never greater than the effort distance in it. However, this lever helps us bymultiplying the applied force i.e. MA is always greater than one in this type of lever.Some of the common examples of the second class lever are wheelbarrow, nutcracker,bottle-opener, oar of a row boat, opening and closing a door, etc. L FE LE L EF FFig 3.8 (a) wheelbarrow (b) bottle-opener (c) nutcrackerc. Third class leverThe liver in which effort is applied at any point E Lbetween the load and the fulcrum is called thethird class lever. This kind of lever is unable F Edto multiply force and change the direction of Ldforce. However, it helps us by acceleratingwork. Fig 3.9 third class leverIn this kind of lever, the effort distance is always less than the load distance. Therefore, thevalue of MA in the third class lever is always less than one. Broom, shovel, sugar tongs,fire tongs, forceps, fishing rod and hammer are some examples of this type of lever.F LF F EL E E LFig 3.10 (a) shovel (b) fire tongs (c) forcepsPoints to remember for the three types of

Spacers, including the hinged section.¼” x 24”W x 18”L plastic panel was laid on top.The wood strips bring the plastic panel exactly level with the ¾” top panel, thus allowing the balls to roll over the plastic panel as part of the bowling alley.Step 17: The Ball Release :Picture # 1 :The balls are returned and stopped by a board at the end of the ball channels. They can be viewed through the plastic panel and their assigned values counted.The balls now have to be released from the ball channels for the next game :Solution : A Lever controls the 4” hinged channel section, aided by 2 springs, one on each side of the Alley. When the lever is pushed down, it pushes down the hinged channel section, and the balls fall down into an open boxed section below it for retrieval.A paint pole was used, with a wide enough hole drilled thru the frame to allow pole maneuverability.Also, when cosmetic finishing is done later, removable side panels will be installed to access both sides of the Alley to service the pole and springs.Picture # 2 :A single spring (with no lever) is added on the other side to help the lever easily control the ball dumping process. Note : the stopper board seen just below the spring … this stops the balls from rolling out on the ball channels straight into the ball box.Note : the 45° bevel of the ball channels in the hinged section … this is needed in order for the balls to clear the ball stopper board when the lever is pushed down to release the balls … yet the beveled ball channels are high enough to still keep the balls in their respective channels until released.This section you see was extended from the Alley to accommodate this catch-n-release lever mechanism and the ball box below it. The bottom panel of the ball box is angled to assure the balls roll to the front.Step 18: We now flip to the other side of the Alley to view the operation of the Lever pole :Picture # 1 :Lever in closed position.Note the spring tension … It is somewhat relaxed, and gives longer life to the spring.Picture # 2 :Lever pushed down half way.Picture # 3 :Lever pushed down all the way. The balls roll out of the channels at this point.Note the spring tension … Open but not aggressively … yet strong enough to easily return the Ball Release back to the closed position. When pressure on the lever is released, the springs gently close the hinged Ball Release channels. This is set by trial and error.Step 19: S E C T I O N #