Mechanisms and Movement

What is a Mechanism? A mechanism takes an input motion or force and creates a desired output motion or force Simple machines or a combination

What are Simple Machines? Simple machines are very basic devices that are used to make things work Often, these simple machines are put together to make more complicated machines

The Six Machines Lever Inclined Plane Wheel and Axle Wedge Pulley Screw

Lever A lever is an arm that is on a pivot This pivot is called a “fulcrum” The force that is being used to move the lever is called the “effort” What the lever is moving is called a “load” The distances between the effort and load to the fulcrum determine how easy or hard it will be to move the load.

Classes of Levers A First Class lever has the fulcrum in the middle, and the effort and load on either end A Second Class lever has the load in the middle, and the effort and fulcrum on either side A Third Class lever has the effort in the middle and the load and fulcrum on either side

Mechanical Advantage Ratio between load and effort moments MA>1 = gain in output force Gain in output force = loss in output motion

Velocity Ratio VR = ratio of distance moved by effort and load MA is gained through loss of VR VR is gained through loss of MA VR>1 means that the effort is moving a greater distance than the load

Inclined Plane The inclined plane is a ramp It is used to make it easier to push something up and down a distance. How hard is it to move a heavy brick up a 10 foot high wall? How hard is it to move a heavy brick up a gradual slope, or inclined plane?

Wheel and Axle Wheels are circular, and axles go through their middle to allow them to spin These simple machines allow for uniform rotation Off-center wheels are called cams and affect motion depending on their shape

Wedge A wedge is a special type of inclined plane A wedge acts to push apart material A fork and knife are both wedges Wedges are used to join things together Nails

Pulley A pulley is used to lift heavy things. A rope or cable is set around a wheel and axle. By pulling on the rope around the wheel, whatever the other end of the rope is attached to will move. This is a simple pulley. Many pulleys in sequence are called compound pulleys.

Screw A screw is a special inclined plane that is wrapped around a central shaft Screws are useful to make really strong connections between materials Screws are also used to slow down a descent without taking up the space of a straight ramp (spiral staircase)

Kinematics Kinematics is the study of movement in a mechanical system Does not regard forces or masses, just movements

Kinematics The individual elements that are used in a mechanism are called members or links. One end is fixed to a point. All links are held together by elements called joints. A combination is called a “kinematic chain.” If the system is incapable of movement, it is no longer a mechanism, but rather, a structure

Motion There are a number of different types of motion. These types of motion can be converted into one another Mechanisms transfer this motion

Linear Motion Straight-line motion that occurs in one direction CD drive on a computer A drawer

Reciprocal Motion Back and forth linear motion Piston in a combustion engine Needle in a sewing machine

Rotary Motion Movement around a center point or axle Very common and very efficient

Oscillating Motion Back and forth movement in an arc A clock pendulum Windshield wipers

Linkages Linkages transmit motion or force to a desired location Change direction Change length Split motion or force over multiple paths

Bell Crank Changes direction of force 90 degrees Brakes on a bike Used to ring church bells Pulling down on a rope would swing bell

Reversing Linkage Changes direction by 180 degrees

Parallel Linkages Allows parts to move in a parallel relationship

Crank and Slider

Treadle Linkage Changes oscillating motion to rotary motion Came from foot-operated pedals for sewing machines and other tools

Toggle Linkage “Snaps” in place Locking pliers Vice grips Locking legs of a foldable table Additional force is needed to unlock the toggle linkage