4. TRANSFORMATION OF MOTION

4. TRANSFORMATION OF MOTION
Some mechanisms transform linear motion into rotary motion. Most of these mehanisms are reversible. They also transform rotary motion into linear motion.
The linear motion can be unidirectional or reciprocating. Reciprocating motions alternate from one side to the other.

4.1. Rotary-linear transformation wheel

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.

Uses: We use rack and pinion mechanisms for sliding doors, conveyor belts and other devices that require precise movements.

Nut and bolt mechanism
A nut and bolt mechanism transforms rotary motion into linear motion. It has two parts: a bolt or shaft with a spiral grove and a nut that turns around it.

Uses: We use nut and bolt mechanisms to hold things together. We also find them in scissor jacks for lifting cars, water tap mechanisms and screw-top bottles.

Winch and crank mechanism
 A winch is a cylinder that rotates around a horizontal axis. We attach a rope to th winch and to a load.
The increase in force is proportional to the ratio between the radius of the crank and the radius of the winch. Thse ratios obey the Law of the Lever.
                                    F x d = R x r
We use winch and crank mechanisms to lift or pull heavy loads.

Uses: We use winches for lifting loads. We find them in construction cranes and in the mechanism that raises window blinds in our homes.

4.2. Reciprocating rotary-linear transformation
 The pedal mechanism of a bicycle transforms the reciprocating movements of our legs into continuous rotary motion.

Crank and rod mechanism
The piston moves a rod forwards and backwards. This rod turns the first wheel. The second wheel turns because it is connected to the first wheel by another rod.
Uses: This mechanism was important for the first steam engines. Today we find cranks and rods in internal combustion engines, as well as windscreen wiper mechanisms. 

 Crankshaft mechanism
We can connect multiple rods to one shaft. The rods are connected to cranks, and the cranks are connected to the crankshaft.
Uses: We use crankshaft for combustion motors that use pistons. We also use them for sewing machines.

 Cam mechanisms
A cam is an irregularly shaped devide 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.
Uses: We can find camshafts in toys, automatic tools and combustion motors.

Some cams are circular, but with an axis of rotation that is off-centre. These are called accentric cams because they rotate in an irregular or eccentric way.
Uses: There are often eccentric cams in sewing machines and other devices that transform rotary motion to linear motion.