Why is a pencil not a system

en contreto podemos establecer emana del latin  y mas exacatamente de la palabra lapiz que puede traducirse como piedra , un lapiz es un instrumento de escritura o dibujo que precenta una barra de grafico  encerrada de un cilindro o otro material                        

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

water and alcohols have similar properties because water molecules contain hydroxyl groups that can form hydrogen bonds with other water molecules and with alcohol molecules, and likewise alcohol molecules can form hydrogen bonds with other alcohol molecules as well as with water.