un bloque de pierda de 1960 n descanza sobre el pioso de madera,¿que fuerza horizontal (fr) se requiere para moverlo, si se concidera un coeficiente de ?razonamiento de estatico us=0.4

Which of the following is part of the explanation or description of electromagnetic waves? (select all that apply) a. electrically charged molecules in a medium transfer their energy to nearby electrically charged molecules. b. a changing electric field causes a changing magnetic field. c. magnetic molecules in a medium transfer their energy to nearby magnetic molecules. d. a changing magnetic field causes a changing electric field.