SPEED RATIOS.

The relationship between the speeds of the two wheels is inversely proportional to their sizes.
N2/N1: D1/D2.
N: is the speed of rotation.
D: is the diameter of the wheel.
But in the case of gears, we compare the number of cogs or teeth (Z) that each gear has.

CHANGES IN SPEED.

If we want to increase the speed of a rotary system, we must transmit motion from a larger (input)  element to a smaller (output) element. 
If we want to decrease the speed of a rotary system, we must transmit motion from smaller (input) element to a larger (output) element.

ROTARY TRANSMISSION.

These mechanisms have two purposes:
- Transferring rotary force from an input location to another location.
- Changing the rotary speed by using rotating elements of different sizes.
There are various mechanisms:
Friction wheels - Pulleys with belts.
 
Interlocking gears - Sprockets with chains.
 
All of these mechanisms keep the same speed ratios, but each one offers a different advantage.

COMPOUND PULLEY SYSTEMS.

It is a combination of fixed and movable pulleys.
It is also called "block and tackle system".
There are 3 types:
Vertical system and Horizontal system:
 
F: R/2 multiplied by n (n: the number of movable pulleys)
Exponential system: 
F: R/2 to the power of n.

PULLEYS AND COMPOUND PULLEY SYSTEM.

In a system of pulleys, the equilibrium between te forces depends on te path that the rope follows.
PULLEYS: There are two basic types:
FIXED PULLEY: The forces are equal because the rope moves the same distance on both sides. 

F:R (Force: Resisrtance)

MOVABLE PULLEY: The rope follows a double path around the pulleys. We need half the force to lift the same weight as with a fixed pulley.

F: R/2 (Force: Resistance/2)

CLASSES OF LEVERS.

We can divide levers into 3 classes according to the locations of the fulcrum, force and resistance.
CLASS 1: The fulcrum is between the force and the resistance and the effect of the force applied is increased or decreased. 

CLASS 2:  The resistance is between the fulcrum and the force and the effect of the force applied is always increased.

CLASS 3: The force is between the fulcrum and the resistance and the effect of the force applied is always decreased.

Other examples are: a brake levers, a hand crank and the bicycle handlebars.

2-LINEAR TRANSMISSION OF MOTION

1: Levers: A lever is a bar that turns around a point called fulcrum.
Each force produces a specific torque:
Torque: Force x  Distance.
Law of the Lever:
F multiplied by d: R multiplied by r.
F: Force or the effort that we use.
D: Distance from the fulcrum.
R: Resistance or load that we want to move.
r: distance from the fulcrum.

CONSERVATION OF ENERGY AND WORK IN MECHANISMS.

All mechanisms produce the same amount of work that is done to them.
If a mechanism increases force, it must decrease motion and if a mechanism increases motion, it must drecrease force.
In this way,energy and work are conserved.

CLASSIFICATION OF MECHANISMS.

TRANSMISSION OF MOTION: There are 2 types:
-Linear transmission: For example: Lever, pulley or block and tackle.
 (lever)
-Rotary transmission: For example: Belt drive or gears.
 (gears)
TRANSFORMATION OF MOTION: There are 2 types:
- Rotary-linear: For example: Wheel or rack and pinion
 (rack and pinion)
-Reciprocating rotary-linear: For example: Crank and rod or crankshaft.
(crankshaft)
MOTION CONTROL: There are 2 types:
-Direction control: Ratchet control or freewheel.
-Speed reduction: Brake.
ENERGY ACCUMULATION:
-Absorption/ Dissipation: Spring.
-CONNECTION: There are 2 types:
-Linkage: Clutch.
-Support: Plain bearing.