Notes

STRUCTURES
functions:
>spanning between points
>supporting a load
>protecting things
>containing things

classifications:
>natural vs manmade
>frame vs shell (structures can be made up of a combination of both)

loads and forces:
>structures are designed to withstand different types of forces
-external forces or loads that act on the structure
-internal forces or loads that act within the structure
-eg. on a hot air balloon, passengers are the external forces while the hot air is the internal forces acting on the balloon

loads:
>static force is a force applied without any build up in energy and does not cause any change in size, position, direction on or within a structure
>dynamic force is a force applied with a change in the level of energy and causes a change in size, position, direction on or within the structure

forces:
>tension
-structure subjected to pulling is under tensile force
-eg. tug of war when people at both ends are pulling the rope and the rope would be under tension force
>compression
-when forces are aligned to each other, they are called compression forces
-eg. pushing down on a syringe, the spring would be under compression force
>bending
-structure that is subjected to external force causing it to bend is called bending
-eg. bending wires to fit in a circuit, the wires would be under the force of bending
>torsion
-structure that is subjected to twisting is under stretching force
-eg. wringing a wet towel, the towel would be under torsion force
>shear
-structure that is subjected to sliding is under shear force
-eg. sliding down a slide, the person would be under shear force

reinforcing structures:
>structures made stronger by adding small amounts of material at the right places, adding strength this way is called reinforcing a structure
>gusset plate
-thick sheets of material used to add strength to a joint
-increase area of joint and help to distribute stress more evenly
>braces/webs
-add strength to a joint
-commonly used in shelf, wall brackets, cantilever beams and supporting other structures like street lamps

MECHANISMS
simple machines:
>inclined plane
-ramp or slope
-easier to raise a heavy object by pushing or pulling it up an inclined plane than lifting it straight up
>wedge
-piece of triangular shaped material used to push things apart
-split rocks, logs, blocks of ice and even metals
>lever
-bar or rod that turns around a fixed point (the pivot)
-help lift or move heavy objects
>wheel and axle
-wheel is a circular object, normally connected to a rod or axle of smaller diameter
>screw
-consists of inclined plane wrapped around it
-produces large force when turned with small force
>pulley
-consists of wheel and groove along its edge, for holding a rope of cable
-help lift heavy loads
-pulling rope on one side of pulley raises load on other side

linkages:
>two or more rods linked together to take movement from one place to another
>linkage is a combination of levers

gears:
>wheels with teeth
>two gears normally placed edge to edge with contact teeth locked together so when one gear rotates, the other gear also rotates
>different speeds of rotation can be generated by connecting gears of different diameters

transition of motion:
>all gears have it
>take motion (movement) from one place to another
>when a gear turns on shaft, it causes the gear to turn on another shaft
>when one end of the lever moves down, the other end moves up

motions:
>linear
-move in straight lines
>rotary
-rotate
>reciprocating
-move back and forth
>oscillating
-swing

conversion of motion:
>one kind of motion changed to another kind
>crank and slider mechanism
-converts rotary to reciprocating motion
>rack and pinion mechanism
-converts rotary to linear motion
>cam and follower mechanism
-converts rotary to reciprocating motion
>bevel gears
-changes axis of rotation
>4-bar linkage
-converts rotary to oscillating motion

ORTHOGRAPHIC PROJECTION
>Front Elevation, End Elevation, Plan
>each square=5mm*5mm
>all dimensions are in mm
>leave spacing of two squares from top and left of paper and from horizonal and vertical lines
>FE and EE are at same level and same height
>FE|EE
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