5.1 DIRECTION CONTROL:RATCHETS:
A rached is a mechanism that controls the direction of motion.Some ratchets are reversible,so they can turn and lock in one direction or another.

5.2 SPEED REDUCTION:BRAKES:
Brakes use friction to reduce speed.They are activated by certain levers.The lever transmits forcé to an output receptor,which puts pressure on the Wheel.There are various types of brake systems according to where the friction is produced:

• Disc brakes:A disc is connected to an axle.Brake pads apply pressure to the disc.
• Band brakes:A drum is connected to an Axle.A flexible band applies pressure to the outside of the drum.These brakes were used in carriages and they depended on the strength of the driver.
• Drum brakes:A drum is connected to the axle.A pair of brake shoes apply pressure to the inside of the drum.
   
  
  

Cam mechanisms:A cam is an irregularly shaped device that rotates on a shaft.When the cam rotates,it pushes a special bar called a follower.The follower can move other parts or it can turn a switch on and off.Some cams are circular,but with an axis of rotation that is off-centre.These are called eccentric cams because they rotate in an irregular or eccentric way.

Crankshaft mechanism:We can multiple rods to one shaft.The rods are connected to cranks,and the cranks are connected to the crankshaft.A crankshaft mechanism can synchronise the movements of various parts,such as the multiple pistons of a car engine.

4.2 RECIPROCATING ROTARY-LINEAR TRANSFORMATION:
The pistons of a car engine produce into continuous rotary motion.Some mechanism work in the opposite way,transforming rotary motion into reciprocating linear motion.

Crank and rod mechanism:The piston moves a rod forwards and backwards.This rod turns the first Wheel.The second Wheel turns becouse it is connected to the first Wheel by another rod.

4.1 ROTARY-LINEAR TRANSFORMATION WHEEL:
they let us move more easily because they reduce our contact with the ground and decrease friction. However,if there isn't enoungh friction, the wheels can slide out of control.
With each rotation, a Wheel moves forward a distance that is equal to its circumference.As a result,we need less force to move vehicles with larger wheels and they move more quickly.

Rack and pinion mechanism:The rack is a bar with many teeth and the pinion is a gear with teeth that interlock with the rack. When the pinion rotates,the rack moves in a linear direction.

Nut and bolt mechanism:A bolt or shaft with a spiral Groove and a nut that turns around it.We can turn and lighten the nut in order to hold things together.We can a use a nut and bolt mechanism to lift loads because it fuctions as a reducing system.

Winch and crank mechanism:A winch is a cylinder that rotates around a horizontal axis.Then we turn the crank to rotate the winch.The rope rolls up around the winch and lifts the load.The crank increases the force and the winch transform rotary motion into linear motion.The increase in force is proporcional to the ratio between the radius of the crank and the radius of the winch.

F*d=R*r

3.5 WORM DRIVE:
A worm drive has two parts: a worm shaft and a worm gear. The shaft has two, three or even more grooves.Each Groove interlocks with one tooth of the worm gear.

Worm drive:

3.3 BELT DRIVES AND GEAR TRAINS:
A belt drive is a system of pulleys connected by belts.Each belt connects pair of pulleys,so they turn together.
To understand how a belt drive Works,we can analyse the example above:

• Wheel 1 turns Wheel 2,which moves faster because it is smaller.The size ratio between the wheels is D1/D2=1.5. If Wheel 1 makes 1 rotation,wheel 2 makes 1.5 ratations.
• Wheel 2 and Wheel 3 are connected to the same axis,so they turn together. If Wheel 2 makes 1.5 rotations,wheel 3 also makes 1.5 rotations.
• Wheel 3 turns Wheel 4,which moves faster becouse it is smaller.The size ratio between the wheels is D3/D4=2. If Wheel 3 makes 1.5 rotations,wheel 4 makes 1.5*2=3 rotations.

to calculate the ratio of transmission between the first Wheel and the last Wheel of a belt drive,we must multiply the ratios of transmission of the first pair of wheels and the second pair of wheels:

• N4/N1=D1*D3/D2*D4

3.4 CHANGES IN DIRECTION AND ROTATION:
We can use various system to change the direction of rotation or the axis of rotation in a belt drive.We can also vary the distance between the wheels.With belts,we can change the direction of rotation and the axis of rotation quites are more precise and they transmit more rotary force,or toque.

Parallel Axes:

Pendicular axes:

Crossed axes: