Section A: Mechanical Devices Flashcards
What do mechanical devices do
change one form of force into another
input and output motion
Name the 4 movements
linear- one dircetion staright line
reciprocating- drone up down/back forth
rotary- movement on/around axis
osciliating- back and forth on curved line
What components do levers cosist of
fulcrum- pivot point
effort- input force
load- out force
How do you calculate the mechanical advantage
MA= Load/Effort
MA of n
ratio
What is a first oder lever (first class)
fulcrum between force and load
Eg pliers
What is second order lever (class 2)
fulcrum at one end with effort at opposite end and load anywhere in middle
Eg wheelbarrow
What is third order lever (class 3)
fulcrum at one end and effort applied in the middle
Eg tweezers
What is a linkage
a mecahanism made by connecting rigid parts. they change the magnitude, direction, transform of a force
Explain a push pull linkage
maintains direction of input motion so that output travels in the same direction
Explain bell crank linkage
changes direction of input motion through 90*
used to change horizontal motion into vertical motion vice versa
What are rotary systems used for
drive mechanisms in equip and machinery
transfer direction of force along different paths and through changes of angle and direction
What is a cam
used to change rotary motion into reciprocating motion through use of a follower(movess up/down)
Describe a circular/eccentric cam
steady rise and fall
Describe a pear cam
rapid rise and long dwell (rest)
Describe snail cam
long dwell (rest) and steady rise with sudden drop
only turns in one direction otherwise jam
Describe heart shaped cam
slight rise and fall with no rest period
What are gears
toothed wheels that mesh to transfer one motion from one part of a machine to another
found in cars, clocks, bicycles, can openers
Explain the dirve gear
input turns the driven gear (output)
gears turn opposite directions
Explain an idler gear
a smaller gear placed inbetween bigger ones to make sure they go the same way
transfers movement from drive gear to driven so size doesn’t affect speed
driven gear is one after drive gear
How do you calculate gear ratio
number of teeth on driven gear/ no teeth on drive gear
for every rotation of drive gear, driven does twice as many- gearing up
How to calc velocity ratio
divide drive gear/driven gear
What do pulleys do
help lift load
transmit rotary motion and force
not suitable for high torque due to tendancy to slip
belts are made from reinforced rubber or high strength material like kevlar
Describe a fixed pulley
wheel with a groove and rope that sits in it
allows to change direction of force needed
lifting easier
Describe block and talckle pulley
use of 2/+ pulleys one fixed one moveable to help reduce amount of effort needed
provides mechanical advantage load easier to lift
Explain the drive belt loop
loop of flexible rubber
connects 2/+ pulleys together
belt transfers power from pulley to recieving system
Eg in car belt transfers engine power to lternator to recharge battery
