Write the condition to multiply the effort with the help of simple machine
Answers
Answer:
Machines are device that are used to make our work simpler, easier and faster. They work by changing direction of motion or by multiplying force.
Terms – related to simple machines
Input: - energy supplied to a machine (work done on machine)
Load; - the resistance force to be over come by the machine
Effort: - force applied to a machine to over the resistance force
Mechanical Advantages
· the ratio of the load to the effort M A = L/E
Velocity ratio of a machine = Velocity of the effort (VE)
Velocity of the load (VL)
Efficiency () = work done by the machine (Wo)
Work done by the machine (Wi)
Their relationship
= MA
-------
V. R
% = M A
-------- x 100
V.R
Functions of machines
1) Force multiplier- in jack used to lift a Car
2) To change the point of application of the effort at a convenient point- lifting car , bus etc at a service station ( work shop) for washing & repairing
3) Change the direction- single fixed pulley use for hosting flags lifting water from wall
4) To obtain gain in speed- gear system used in automobiles
Levers:
It may be better remembered as -FLE
Fulcrum in the middle - first class lever
Examples- crowbar, see-saw, pliers, beam balance
First class lever can have varied mechanical advantage according to the position of load with respect to the effort from fulcrum.
Load in the middle – second class lever.
Examples- bottle opener, wheel barrow, nut cracker
Second class lever has mechanical advantage always more than one as load is in between fulcrum and effort making the effort arm longer than the load arm. It multiplies force.
Effort in the middle – third class lever
Example- table knife, sugar tongs, forceps, knives, spades
A third class lever has mechanical advantage always less than one as effort being in between load and fulcrum; effort arm is shorter than the load arm. It does not multiply force but changes the direction of force.
Distance between effort to fulcrum is effort arm and load to fulcrum is load arm.
A lever works under the principle of moments which states that the total anticlockwise moments is equal to the total clockwise moments.
Moments due to the efforts = Moments due to the load
Effort ´ Effort arm = Load ´ Load arm.
L is MA for all machines
E
EA is MA specifically for levers.
LA
L ´ LA = E ´ EA
Mechanical advantage:
It is the ratio between load to effort. It has no unit.
Inclined Plane:
Steps, planks used for loading heavy things on a truck, step-like path made for taking things to a high up construction site, etc. are examples of inclined plane. It multiplies force at the expense of distance.
p= length of the plane
h = vertical height of the plane.
L= Load
E = Effort
From work energy principle
L´h = p´E
L = p = MA
E h
Pulleys:
It is simple machines which helps us to lift heavy loads when we apply effort in suitable and convenient direction.
Single fixed pulley:
It does not multiply force but the effort can be applied in a convenient direction which is towards the pull of the earth.
L = 1T
E = 1T
Mechanical advantage is one: It means that same amount of effort is required to lift a load or in other words, force is not multiplied.
Single movable pulley:
It multiplies force but the effort has to be applied against the pull due to the force of gravity.
L = 2T
E = 1T
MA is 2: It means that the effort required to lift the load is half of the load.
Combination of single fixed and movable pulley:
L = 2T
E = 1T
MA = L = 2T = 2
E 1T
It not only multiplies force but also the effort can be applied downwards.
Velocity Ratio:
It is the ratio of the distance moved by effort to the distance moved by load.
VR = de
dl
It has no unit as it is a ratio.
de = distance moved by effort.
dl = distance moved by load.
Block and tackle:
It is the combination of pulleys in different blocks.
[For four pulley system]
L = 4T, E = 1T
MA = L = 4T = 4
E 1T
It gives ideal mechanical advantage but actual mechanical advantage will always be less than that.
In general, M.A is equal to the number of pulleys used and velocity ratio is equal to the number of strands of the rope supporting the load.
Efficiency:
It is the ratio of the mechanical advantage to the velocity ratio.
…..&
Efficiency = MA
VR
Thus
Gears:
It is simple machines that have teeth or cogs at its rim
The teeth or cogs of different sized gears are so constructed to fit within the other and influence one another. The one which influences the other is called as driving gear while the one getting influenced is called as driven gear.
Gears are used to multiply force or to multiply speed.
Speed multiplication = No of Cogs in Driving Gear
No of Cogs in Driven Gear
More number of teeth in driving than driven gear
Force Multiplication = No of Cogs in Driven Gear
No of Cogs in Driving Gear
More number of teeth in driven than driving gear
Explanation:
Mechanical advantage is one: It means that same amount of effort is required to lift a load or in other words, force is not multiplied. Single movable pulley: It multiplies force but the effort has to be applied against the pull due to the force of gravity.07-Jun-2021