Machines Flashcards
functions of simple machines
- force multiplier
- speed gainer
- changing point of application of effort to a convenient point
- changing direction of effort to a convenient direction
define machine
a machine is a device by which we can either obtain a gain in speed or overcome a large resistive force at some point by applying a small force at a convenient point and in a desired direction
define load
a resistive or opposing force to be overcome by a machine
define effort
a force applied on the machine to overcome the load
define mechanical advantage
ratio of load to effort is called MA
force multiplier
when MA is greater than 1
VR greater than 1
speed gainer
when MA is lesser than 1
VR less than 1
machine having MA equal to 1
change the direction of effort as there is no gain in force or speed
define VR
ratio of velocity of effort to velocity of load is called VR
ratio of displacement of effort to displacement of load
when VR equal 1
displacement of load is equal to displacement of effort. change in direction
define work input
word done on the machine by effort
define work output
work done by machine on the load
define efficiency
ratio of the work done on the load by the machine to the work done on the machine by the effort
define ideal machine
machine in which there is no loss in energy in any manner, work output = work input
efficiency= 100%
loss of energy caused by
- moving parts are not frictionless
- string in it is not perfectly elastic
- different parts are not perfectly rigid
relationship between efficiency, MA, VR
MA of a machine is equal to the product of its efficiency and VR
define lever
a rigid, straight/bent bar which is capable of turning about a fixed axis
law of levers
the MA of a lever is equal to the ratio of the length of its effort arm to the length of its load arm
three classes of levers
ELF: 3, 2, 1
class 1 levers
MA and VR can have any value, either greater than, equal to, or less than 1
class 2 levers
effort arm is always longer than load arm
MA and VR are always greater than 1
force multiplier
class 3 levers
effort arm is always shorter than load arm
MA and VR always lesser than 1
speed gainer
two pulleys
- single fixed pulleys
- movable pulley
define single fixed pulley
a pulley which has its axis of rotation stationary in position
both load and effort act downwards , tension acts upwards
MA is less than 1
VR is equal to 1
use of fixed pulley
to change the direction of the effort to be applied
single movable pulley
a pulley whose axis of rotation is movable
load can be lifted by applying an effort equal to half the load, in ideal situation
force multiplier
MA is less than 2
VR is 2
two ways of combination pulleys
- using one fixed pulley and several movable pulleys attached to the same rigid support
- using several pulleys in two blocks, when lower block is movable and upper block is fixed (block and tackle)
MA and VR for combination pulleys
2 to the power of n movable pulleys with one fixed pulley
effort required to balance a load in block and tackle system
load/ number of pulleys
block and tackle acts as
force multiplier
VR and MA of block and tackle
equal to the number of strands of the tackle
