Machines Flashcards
Force multiplier means
by lifting a heavy body by applying less amount of effort
rear wheel of cycle is an example of ______.
changing the point of application of effort to a convenient point .
lifting bucket from the well is an example of
changing direction of effort to a convenient direction
machines also work as obtaining ______ in speed
gain , greater movement of load by less movement effort
gain in speed formula -
gain in speed = 1/ velocity ratio
define machine -
machine is a device by which we can overcome a large resistive force by applying less effort at convenient point and desired direction or by which we can obtain gain in speed
Load means
a resistive or opposing force to be overcome by a machine
effort means
force applied on a machine to overcome a load
mechanical advantage -
ratio of load and effort
mechanical advantage - formula
load / effort
when the mechanical advantage be less than 1
when the effort is greater than load
when mechanical advantage is greater than 1
when effort is less than load
when the M.A is 1
when effort = load
if mechanical advantage is more than 1 the machine acts as
force multiplier
if a machine as M.A less than 1
it acts as gain in speed
if m.a = 1
it generally acts to change the direction of effort
machine can’t be used as force multiplier as well as speed multiplier [simultaneously ] why?
in force multiplier - effort < load , in speed multiplier - effort > load
velocity ratio means
ratio of velocity of effort/ load
velocity ratio [as displacement ]
ratio of displacement of E/ displacement of L
when is velocity ratio be less than 1
displacement of load is more than displacement of effort
when velocity ratio is less than 1 it called as
gain in speed
when is velocity ratio is more than 1
when displacement of load is less than displacement of effort
when velocity ratio is more than 1 machine acts as
force multiplier
velocity ratio = 1 if ?
displacement of load = displacement of effort ,
if a machine as velocity ratio = 1 such machines generally does
change in direction of effort
work input means
work done on the machine by effort
work output
work done by the machine on the load
efficiency means
ratio of work output / work input
efficiency denoted by
η [eta]
when mechanical advantage decreases
due to friction and weight of the parts
if mechanical advantage decreases _________ decreases
efficiency
load point means
the point were the energy is obtained by overcome the load
effort point
point at which energy is supplied to machine by applying effort
input energy
work done at the effort point
output energy
work obtained at the load point
no machine has efficiency _________
greater than 1 [ more than 100%]
output energy can never be greater than input energy why ?!
it will violate law of conservation of energy
what is ideal machine ?
a machine in which there is no loss of energy [ no dissipation of energy in undesired form ]
in ideal machine work output is = _____
work input
in ideal machine efficiency is _____
100%
what is mean by actual machine ?
machine which has loss of energy , work output is not equal to work input
how loss of energy happens in machine [ actual ]
due to weight of parts and friction , string is not perfectly elastic , different parts are non rigid
in actual machine most prominent loss of energy is due to
friction , energy loss by heat
how will a machine heated
some energy’s will lost as heat which heats the moving parts of machine
if efficiency of machine is 80% what does it means ?
80% energy is obtained as useful energy , 20% lost in overcoming friction
formula for work output -
load * displacement of load
work input - [formula]
effort * displacement of effort
Efficiency = [in terms of M.A and V.R ]
m.a / v.r
in ideal Machine - M.a is _____ to v.r
equal
in actual machine - M.A is _________ to V.R
LESS
two types of single pully -
by fixing the axis [ fixed position ] , by changing it axis of rotation [ movable pully ]
single fixed pully means
pully which as its axis of rotation stationary
what happens if tension throughout the string is not same ?
string will move even when the pully is not moving
in case of neglecting the friction and mass of string - the m.a , v.r and efficiency of the single fixed pully is
M.A = 1 , V.R = 1 , EFFICIENCY = 100%
IN ACTUAL PRATICE M.A advantage is _____ in pully
less than 1
why is fixed pully used ?
to only change the direction of effort applied
for gain in speed velocity ratio must be less than 1 but for single fixed pully velocity ratio is ________.
always 1
Single movable pully means
pully whose axis of rotation is movable
in neglecting the weight of pully and friction , M.A and V.R is equal to
2
in actual single movable pully - M.A and V.R IS -
m.a less than 2 and v.r remains 2
in actual single movable pully efficiency is
less than 100%
why in actual single movable pully the M.A is less than 2
as we need to give more amount of effort than load
what mean by block ?
a frame which as two or more pully is block
the string passing over the pulleys in block
tackle
in block and tackle system the upper frame as _______ type of pulley
fixed
block and tackle system the lower frame as ______type of pulley
movable
pulley’s in lower block is [ number of pulley’s ]
equal to or less than 1 [number of pully’s ]
effort = __________ [ load and number of pulley’s]
load / number of pulley’s
effort = __________ [ load and number of pulley’s]
load / number of pulley’s
m.a in terms of inclusive of weight
m.a = n-w/e , number of pulley -n , w - total weight of lower block
for greater efficiency in block and tackle system , lower block should be _______
light
