1.5 - Mechanical devices Flashcards
What is a mechanism ?
A device that changes an input motion into a different out motion
What is linear movement?
movement in a straight line
What is reciprocating motion?
Movement backwards and forwards in a straight line
What is a rotary motion?
movement round in a circle
What is an oscillating motion?
movement swinging side to side
What is a lever?
changes an input movement and force into an output movement and force.
What does a lever move around?
a pivot
What does the order of lever depend upon?
load, effort, fulcrum
What is a load?
object being moved
What is the fulcrum?
is the point where the load is pivoted
What is the effort?
the force applied to move a load
What is a first order lever?
has the fulcrum between the effort and load
What is a second order leaver?
has the load and effort on the same side as the fulcrum
What are linkages?
mechanisms that transfer force and can change the direction of movement
What does the number and shapes of the linkage change?
the direction of force
What can the position of the pivots in a linkage change?
size or magnitude of a force
When the pivot is very close to the output end of the lever what happens?
larger force at output
What happens in a bell crank mechanism?
direction of motion is turned through 90 degrees
What is a Cam?
a mechanism with a cam slide and follower.When cam rotates the follower moves up and down
What 3 things can a cam do?
go up, go down, stay still
What are the 6 types of cam?
round, egg shaped, ellipse, eccentric, hexagon, snail
What is a gear train?
a mechanism for transmitting motion and torque
What is a torque?
The turning force that causes rotation
What do gears have?
teeth
If different sized gears are interlocked together what can happen?
They either increase or decrease the speed of rotation and the torque
How do you work out velocity ratio of a gear train?
Velocity ratio = number of teeth on driven gear/ number of teeth on the driver gear
What is friction?
resistance of motion when one object rubs against another
What does the amount of friction depend on?
the material of which the two objects are made
What is a co-efficient of friction?
the amount of friction a material has
How can friction be reduced?
using low co-efficient of friction material or lubrication
What is a rack and pinion mechanism?
can turn rotary motion to linear motion or vice versa
What does a crank and slider mechanism do?
turns linear motion to rotary motion or vice versa
How do you work out load?
mechanical advantage X effort
What is a chain and sprocket mechanism?
transfers rotary motion into rotary motion elsewhere in a machine
What is a sprocket?
a toothed wheel and a chain is made up of links that can pivot and go over the teeth on a sprocket
How do you work out the velocity ratio of a sprocket and chain system?
number of teeth on the driven sprocket / number of teeth on driver sprocket
What is a pulley system?
transmits rotary motion to rotary motion in machines
What will two pulleys connected together on a flexible belt transmit?
rotary motion and torque
How do you work out the velocity ratio of a pulley system?
diameter of driven pulley / diameter of driver pulley
