APUNTES DE FRICCION
https://www.youtube.com/watch?v=LIq1YBJdT3I
https://www.youtube.com/watch?v=xzBAbMd9Ze8
SIMULADOR
https://phet.colorado.edu/sims/html/friction/latest/friction_es.html
EJEMPLOS
https://www.youtube.com/watch?v=Z42EGymMYNM