Presentation on theme: "Lever Pulley Wheel and Axle WedgeScrew Inclined Plane."— Presentation transcript:
Lever Pulley Wheel and Axle WedgeScrew Inclined Plane
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.
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 machine It is a unit less quantity.
VELOCITY RATIO: It is a ratio of velocity of effort to the velocity of the load. Where, VELOCITY OF EFFORT = d(e) / t and VELOCITY OF LOAD = d(l) / t Therefore, we have VELOCITY 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.
EFFICIENCY OF A MACHINE: It is defined as the ration of work output to the work input. Efficiency η = work output = W OUT / W IN work input work 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.
According to law of conservation of energy, work output cannot be more than work input. W IN = E × d(e) W OUT = 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 × η Note: In practice, due to friction M.A. < V.R. So efficiency is always less than 1 Efficiency η = work output = W OUT / W IN work input
It is a rigid, straight or bent bar which is capable of turning about a fixed axis. It has four components 1. Rigid straight or bent bar 2. Load 3. Effort 4. Fulcrum
It works on the principle of moments Effort × effort arm = Load × load arm Load = Effort arm Effort load arm But, M.A. = load / effort Therefore, M.A. = Effort arm Law of Levers Load arm
First Class Lever
. Common examples of first-class levers include crowbars, scissors, pliers, tin snips and seesaws.
Second Class Lever
Examples of second- class levers include nut crackers, wheel barrows, doors, and bottle openers.
Third Class Lever
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.
M.A. = Load / Effort = W / W sin A = 1/ sin A Therefore from the geometry of the figure We have as follows, M.A. = l/h l = slant height of inclined plane h = height of the inclined plane V.R. = d(e) /d(l) V.R. = l/h Hence efficiency η = M.A. / V.R. = 1
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
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
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.
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.
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.
Gears are toothed wheels which interlock to form simple machines. The tighter the joint, the less chance of slipping Gears range in size but the important number is how many teeth a gear has.
It 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.
V.R. = No. of rotations per second of the driving gear ( n A ) No. of rotations per second of the driven gear ( n B ) n A is inversly proportional to R A, similarly for n B and R B. therefore we have, n A = R B = V.R. n B R A Also R B = N B ; Where N are no. of tooth in respective gears A and B R A N A
Automobiles 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.