In this unit I’ve learned lots of things about mechanisms and machines that before I didn’t know. First of all, now I can recognize the six basic simple machines, which are the lever, the screw, the pulley, the wheel and axle and the wedge.

· The lever: it helps us lift things with less effort. A lever can be described as a long rigid body with a fulcrum along its length. They can be classified in three groups depending where the fulcrum, load and force is applied.

o 1^st class: the fulcrum is between the load and the effort.

o 2^nd class: the load is between the fulcrum and the effort.

o 3^rd class: the effort is between the fulcrum and the load.

§ One example could be the bottle opener.

· The screw: it consists of a long and thin metal shaft with threads spiraling along its length. It also has a turning head with a groove where a screwdriver can be used to rotate the screw. It converts rotational motion into linear motion.

o A really common example could be the bottle lid that we use to close the bottle.

· Inclined plane: when we reduce the effort to take something up by increasing the distance. For example if we have to lift somebody who is on a wheelchair we will use and inclined plane to reduce the effort but we will increase the distance.

o A slope would be an example of our daily life, due that every day when we go to the school there are a lot.

· Pulley: a basic pulley comprises of a wheel on a fixed axle, with a groove along the edges to guide a rope.(Foto). It is used to lift thins easily such as heavy boxes. When you put two or more wheels together, and run a rope around them you make less effort and you have created a great lifting machine.

o A daily life example could be a water well.

· Wheel and axel: when we have to move really heavy objects, we have to use a big amount of force to push it. This is due to friction (force resisting the motion of the object on the ground) and the gravitational force (force that pulls the object to the ground). In this simple machine, a wheel is locked to a central axle and they rotate each other when a force is applied on either of them.

o A daily life example would be part of the wheelbarrow, that workers use it to lift debris.

· Wedge: the wedge is the active twin of the inclined plan. But unlike the inclined plane which is stationary, a wedge does useful work by moving. For a wedge, the effort is applied to the vertical edge of the wedge. We can use it to lift heavy loads or to hold an object in place and avoid it from moving.

o Examples of wedges that we use every day could be a knife, saw…

Types of motion

· Linear motion: moving one way in a straight line. Example: direction of a train.

· Reciprocating motion: moving forwards and backwards in a straight line. Example: the follower of a cam.

· Oscillating motion: moving forwards and backwards in an arc. Example: swing

· Rotary motion: moving in a circle. Example: wheel

A mechanism is a device which takes an input motion and force, and outputs a different motion and force. The mechanisms are used to simplify a job. The mechanisms most commonly used in mechanical systems are levers, linkages, cams, gears, and and pulleys.

· Levers: is a long rigid body with a fulcrum along its length. They can be classified in three groups depending where the fulcrum, load and force is applied.

· Linkages: Linkages are mechanisms which allow force or motion to be directed where it is needed.

o Linkages can be used to change:

§ The direction of motion

§ The type of motion

§ The size of a force

o There are four different types:

§ Reverse-motion linkage

§ Parallel-motion linkage

§ Bell-crank linkage

§ Treadle linkage

· Cams: it is a shaped piece of metal or plastic fixed to a rotating shaft. 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.

o Types:

§ Pear-shaped cam

§ Eccentric cam

§ Drop cam

· Gears: it consists of toothed wheels fixed to shafts. The teeth interlock with each other, and as the first shaft (the driver shaft) rotates, the motion is transmitted to the second or driven shaft. The motion output at the driven shaft will be different from the motion input at the driver shaft.

o Types:

§ Rack and pinion