Tension
Pulling force exerted by each end of an object such as a string or rope.
Torsion
A twisting force
Compression
A pushing force/ being squashed
Bending
A bending force is applied at an angle causing a material to be in compression and tension at the same time.
Shear
A force across a material, eg scissors cut by applying a shear force.
Mechanical advantage
Load ÷ effort
It allows change of direction force, making lifting easier but weight will feel the same.
Fixed pulley
Uses two or more pulleys, one fixed, one moveable. Reduces efforted needed to lift. Provides mechanical advantage.
Block and tackle pulley
Linear
One direction
Reciprocating
A back and forth movement.
Oscillating
swinging back and forth
Rotary
Mechanical advantage
Making something easier to move/ lift.
First order lever
Have fulcrum between force and load e.g. Pliers
second order lever
Have fulcrum one end, effort at the opposite end, load in the middle e.g. Wheelbarrow.
third order lever
Fulcrum one end, load opposite, effort in the middle e.g. Tweezers
Push and pull linkage
It maintains the direction of the input motion- meaning that the output motion goes in the same direction.
Bell crank
It changed the input motion by 90 degrees. Making vertical motion horizontal or horizontal vertical.
Circulatory cam
Steady rise and fall
Pear cam
Rapid rise and fall with long dwell
Snail cam
long dwell followed by steady rise and sudden drop can only turn in one direction
Heart cam
Slight rise and fall with no dwell period
Torque
The force that causes rotation
Cam (rotary system)
Mainly used to change rotary motion into reciprocating motion through use of a follower.
Follower (rotary system)
The thing moving up and down.
Crank (rotary system)
Used to rotate the shaft, which rotates the cam.
Gears
Toothed wheels that mesh to transfer motion from one part of a machine to another.
Gear train
Transmit rotary motion and torque (causes rotation). Different sized gears increase/ decrease speed of rotation.
Driver gear
The driver gear (input) turns the driven gear (output). the gears turn in opposite direction.
Idler gear
Used to change direction of rotation so driver gear turns in the same direction as driver gear. Size does not affect speed.
Velocity ratio
Speed of driver gear / gear ratio
Best velocity ratio
Large driver gear with small driven gear.
Gear ratio
Number of teeth on driven gear/ number of teeth on driver gear e.g. 20: 40 = 1:2
Belts
A drive belt (loop of flexible rubber) connects two or more pulleys together and the belt transfers power from the pulley to receiving system.