Mechanical systems Flashcards
What do mechanisms do
they change the magnitude and direction of force
What are mechanical systems
systems that have mechanisms which transform an input motion and force into an output one
types of motion
linear
oscillating
rotary
reciprocating
what is linear motion
moving one way in a straight line
what is rotary motion
moving in a circle ( wheel)
what is reciprocating motion
moving backwards and forwards in a straight line such as a piston
what is oscillating motion
moving backwards and forwards in an arc motion, such as a swing
what do levers do
they move and lift loads by rotating around stationary points called fixed pivots/ fulcrum
what are levers
a rigid bar resting on a pivot/ fulcrum
summarise a first order lever
- fulcrum or pivot in between effort and load
- longer lever, less force required
- e.g - scissors, grass cutters
summarise a second class lever
- load in between fulcrum (Pivot) and effort
- e.g. wheelbarrow, car door, nutcracker
- the closer together the fulcrum and load, the easier to lift
summarise a third class lever
- effort in between the fulcrum and load
- moving the fulcrum and effort further apart makes the load easier to carry
- e.g. fishing rods, chopsticks, tweezers
What do linkages do
change the magnitude of the force and direction of motion
Describe a push/pull linkage
- use two fixed pivots
- input and output motions of the linkage are in the same direction but the motion of the link arm is in the opposite direction
- changing the position of the pivots will change the magnitude of output force
what do moving pivot points do
keeps link arm together
what do fixed pivot points do
keeps link arms parallel so anything put on won’t tip over
Describe a bell crank
- changes direction of force through 90 degrees
- magnitude of output force can be changed by moving the fixed pivot so it’s not an equal distance between the two moving pivots
Describe reverse motion linkage
changes direction of motion
the input and output don’t move in the same direction
used for foldable clothes horses
Describe a crank and slider linkage
- can change motion, e.g. oscillating to linear
- the fixed pivot point anchors linkages to one place
- the lever moves forwards and backwards in a slider
-used in car engine
What are gears
toothed wheels that interlock
what do gears do
transfer motion from one part of a machine to another
what is a gear train
where two or more gears are linked together
what are gear trains used for
to change direction of motion/ change the magnitude of the input force
What does the driver gear do
The driver and driven will turn in opposite directions when turned
What happens when you use a third gear (idler) with a driver and driven gear
the driver and driven gear will turn in the same direction, the size of the idler won’t alter the speed of the other two gears
how does the size of a gear relate to the speed
a smaller gear or the one with fewer teeth will turn faster
how to find the gear ratio
gear ratio = number of teeth on the driven gear / number of teeth on the driver gear
how to find output speed
speed or driver gear (input speed) / gear ratio
