英语流利说 Level5 Unit3 Part4 listening: Electromagnetic Force&Magnetic Field Reversal
ElectromagneticForceThereareseveralfundamentalforcesthatholdouruniversetogether.Oneofthese,ofcourse,isgravity,theforcebetweenobjectsthathavemass.Anotherimportantforceistheelectromagneticforce.Theelect