MACHINES AND

MECHANISMS

Dept. Tecnologia IES Cap de Llevant

MACHINES

They are used to avoid or reduce the human efforts in order

to do a work.

SIMPLE MACHINES

WHEEL INCLINED

PLANE LEVER

SPIRAL PULLEY

ELEMENTS in a MACHINE

MECHANISM

It is a device which takes an

input motion and force, and

outputs a different motion

(output) and force. The

point of a mechanism is to

make the job easier to do.

STRUCTURE

It is an element or a group

of elements that bear forces

in a machine (like a bicycle)

or in a static system (a

bridge or a building).

INPUT

(your effort)

MECHANISM OUTPUT

(load)

REVERSIBLE / NON REVERSIBLE MECHANISMS

REVERSIBLE MECHANISMS are those mechanisms where you

can use the output as an input and the input as an output. For

instance: a seesaw.

INPUT

(your effort)

MECHANISM OUTPUT

(load)

NON REVERSIBLE MECHANISMS are the mechanisms with only

one input and one output. For instance: a car jack.

THE MECHANISMS

How can a bicycle move?

How can the wheels of this machine turn?

How can we get the water from this water well?

Pulley

String

Turn of the pulley and the shaft

Resistance

TYPES OF MOTION IN MECHANISMS

Some mechanisms have the same kind of motion for input and output:

Linear Motion Linear Motion

Rotary Motion Rotary Motion

Other mechanisms take one type of input motion, and output it as a different

type of motion.

Linear Motion Rotary Motion

Rotary Motion Linear Motion

TYPES OF MOTION IN MECHANISMS

There are two basic types of motion in mechanical systems:

LINEAR MOTION is motion in a straight line.

ROTARY MOTION is a circular motion.

LEVERS

LEVERS

A lever is the simplest kind of mechanism.

It is composed by:

The load is the object you are trying to move.

The effort is the force applied to move the load.

The fulcrum (or pivot) is the point where the load is pivoted.

When we apply a force (F1) in a point of the lever, we are creating a linear

motion, which transforms in another linear motion and a Resistance Force (F2)

appears.

F1: Applied force or Effort

F2: Load or Resistance

L1: Effort arm (distance)

L2: Resistance arm (distance)

F2 Load or

Resistance

Force or Effort F1

Resistance arm

L2

Effort arm

L1

Fulcrum

LAW OF THE LEVER

The formula is:

F1 x L1 = F2 x L2

Units:

F = Newtons (N) = m (kg) x g (10 m/s2)

L = metres (m)

The longer is L1, the less force you must do (and the other way around).

F1 F2

L2 L1

Example (calculation about levers):

Joan and Anna are seated in a swing. The distance between Anna and the fulcrum is 5m and her weight is 300 N. Joan is at a distance of 3m from the fulcrum.

How many Newtons must weight Joan to raise her?

NL 5003

53002

F1 x L1 = F2 x L2

300 x 5 = F2 x 3

Joan

F2 Anna

300 N

L2 = 3m L1 = 5m

TYPES OF LEVERS

Class 1 levers: has the fulcrum between the effort and the load.

Ex: scale, pliers, crossing gate barrier,...

Load Effort

Fulcrum

Class 2 levers: have the load between the effort and the fulcrum.

Ex: wheelbarrow, nutcracker,...

TYPES OF LEVERS

Load Effort

Fulcrum

Class 1 and class 2 levers both provide mechanical advantage.

This means that they allow you to move a large output load with a

small effort.

TYPES OF LEVERS

Load

Effort

The formula to calculate it is:

Mechanical Advantage = Load / Effort

Class 3 levers: have the effort between the fulcrum and the load.

Ex: hammer, tweezers,...

TYPES OF LEVERS

A class 3 lever does not have

the mechanical advantage.

More force is put in the effort

than is applied to the load.

Load Effort

Fulcrum

LINKAGES

LINKAGES are mechanisms which allow force or motion to be

directed where it is needed.

LINKAGES AND TYPES

Reverse-motion linkage Parallel-motion linkage Bell-crank linkage

It changes the direction

of the motion.

It creates an identical

parallel motion. It changes the direction of

movement through 90°

GEARS

GEARS

GEARS are rotating machines with teeth, which mesh with another

toothed part . When the first shaft moves (it is called driver shaft), the

other one (called driven shaft) turns or moves in the opposite direction.

They can have different functions:

· Increase or decrease forces

· Change the direction of the force

· Increase or decrease the speed of rotation.

TYPES OF GEARS

Depending on the teeth shape and the axis position there are

different kind of gears:

Bevel gears

Simple spur gear train Compound spur gear train

Worm gear

We can find them in watches, cassettes, bombs,....

Rack and pinion

GEARS - FORMULA

The formula used to calculate de velocity is:

V1·D1 = V2·D2

V1 = velocity of the driver shaft (rpm: revolutions per minute)

D1 = number of teeth of the driver shaft

V2 = velocity of the driven shaft (rpm: revolutions per minute)

D2 = number of teeth of the driven shaft

CHAIN AND SPROCKET

This mechanism uses a chain and a spur gear (with teeth) called

sprocket

CHAIN AND SPROCKET

The formula used to calculate de

velocity is the same as in gears:

V1·D1 = V2·D2

PULLEY SYSTEMS

PULLEY SYSTEMS

This mechanism is like the Chain and Sprocket, but in this case the

pulley wheels don’t have teeth and they are connected by a belt.

How can they modify the velocity?

MULTIPLY the velocity

Using the bigger pulley shaft like

the driver shaft in order to move

the smaller pulley, which will turn

quicker than the bigger one.

REDUCE the velocity

The smaller pulley drives the

bigger one and this one has a

slower velocity.

REVERSE the direction

It can be done by twisting the belt.

CALCULATE THE VELOCITY OF THE PULLEY

The formula is: V1 · 1 = V2· 2

1 = diameter of the driver pulley (in metres)

V1 = velocity of the driver shaft (rpm: revolutions per minute)

2 = diameter of the driven pulley (in metres)

V2 = velocity of the driven shaft (rpm: revolutions per minute)

ROPE and PULLEY

PULLEYS

A PULLEY is a wheel with a groove along its edge, for holding a

rope or cable.

Pulleys are usually used to reduce the amount of force needed to

lift a load.

Fix pulley

TYPES OF PULLEYS

1.- FIX PULLEY (SIMPLE PULLEY):

It doesn’t reduce the effort we have to do to.

It is like a class 1 lever, but it allows to apply the

effort in the desired direction.

2.- Tackle:

It is formed by a fix pulley and one or more moving

pulleys connected by a rope. One extreme of the

rope is fixed to the pulley shaft and on the other

extreme the force is applied.

TACKLES CALCULATIONS

• When there is one moving

pulley then F=W /2

(Effort = load/2)

• When there are two

moving pulleys then F=W/4

(Effort=load/4)

If there are one or more

moving pulleys, the effort

is reduced.

It can be calculated by the

formula:

F = load/ 2n

n = number of moving pulleys

RATCHET

RATCHET

It is a mechanical device that allows continuous linear or rotary

motion in only one direction while preventing motion in the opposite

direction.

Ratchet mechanisms are used in, for example, load-lifting machines,

since ratchet mechanisms prevent the movement backward under the

weight of the load.

CAMS

It is a shaped piece of metal or plastic fixed to a rotating shaft.

CAM

A cam mechanism has three parts: cam, slide and follower.

The cam shaft rotates continually,

turning the cam. The follower is a rod

that rests on the edge of the turning

cam. The follower is free to move up

and down, but it cannot move from side

to side because of the slide or guide.

TYPES OF CAM

CIRCULAR CAM or

CRANK, LINK AND SLIDER ECCENTRIC CAM

PEAR-SHAPED

CAM

DROP CAM

SCREW THREAD

SCREW THREAD

It is a helical structure used to convert between rotational and

linear movement or force.

A screw thread is the essential feature of the screw as a simple

machine and also as a fastener.