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Well, now we are going to explain pulleys, belts and gears.

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The transmission of movement is really important to have a good work to all of the machines.

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So mechanical system always consists in different pulleys, belts and gears

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which transmits the movement from one part to another.

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This is a type of mechanism.

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Well, if you have two objects with rotation,

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you can discompose the speed in a point that both objects have in common, the touch point.

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And the conclusion of this is that if you want to have a good rotation without any slide,

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you need that the two objects must be cylinders, otherwise the rotation is not good

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good and the transmission of the movement is not constant which sometimes can be or could be

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a problem in some machines. So we can conclude that the two objects that are in touch must be

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the cylinders and the transmission ratio can be expressed in this way with taking into

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consideration the diameter of the ratio of the cylinders which are in touch.

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Well the touch can be in different ways as you can see here and it's also important to

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take into consideration when you have to choose a particular mechanism to particular application.

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So this is the most important thing, the transmission ratio, which is the ratio between the rotation

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Well, so depending the dimension of the wheels which are in touch, the ratio of rotation

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speed can be different also. If the driven wheel is smaller than driven, the rotation

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speed in the driven is higher, is bigger than in the driven, so this type of mechanism is

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usually called multiplication mechanism.

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The opposite case is inverse, so the mechanism in this time is usually called reduction mechanism.

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It's important that you take into consideration that the sense of rotation in the driven wheel

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is opposite to the driver's.

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Well the energy, the energy is always the same value, well you can have some irreversibilities

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but in each way the power is always the same. So what happened? Well, the conclusion is that if you

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have different forces that you want to move, it's opposite, as you can see in this slide.

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well if you want to guarantee in the transmission of the movement because you

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have so many power to move or the speed is too high instead of wheels you can

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you must use gears a gear is a wheel in which you have you have is a wheel with

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teeth in the super files so in this case the teeth must be the teeth guarantee

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the movement from the driver to the driven on is the way they can you have

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difference important thing in a teeth, but not only the number of the teeth in

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the surface and also the relationship between the number and its size,

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the diameter. This is usually called modulum. If you want that two teeth work

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properly both driver and driven must have the same module and in this way

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if you repeat the relationship taking this into consideration

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the transmission ratio can be expressed using the number of teeth

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you have in each gear as you can see in this slide. Sometimes if the

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distance are very very long you can transmit the movement using belts or

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chains. In this case the sense of the rotation is the same but you can change

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the sense of rotation changing also the belts of change and what you have in this slide you

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can have a reverse direction cross the belt for example but if you don't cross the belt

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Well, the rotation is in the same sense in the driver and in the driver wheel.

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And the relation, the transmission ratio is the same, has the same stress.

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Well this is something relating to the stress that the belts must have because obviously

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the transmission is important and they have a little bit of stress in the in the belts

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that is not so important it's just only something to to know it