 Heat energy stored in these motions does not contribute to the temperature of a substance.   This is misleading and misguided.  An improvement would be: 'as the temperature of a substance increases,  the magnitude of motions like these increases'.  Or ' When a body gets hotter, the heat energy supplied is going into motions like these. ' Or ' When a body's temperature is increased,  the heat energy supplied is going into motions like these. '    David MacKay  