Physics preservice students’ understanding and use of of positive (+) and negative (–) algebraic signs applied to conservation of mechanical energy in 1-dimensional motion were explored using three everyday familiar contexts in physics. All 19 students in a class were interviewed about their understanding and use of algebraic signs as applied to high school physics notions of conservation of mechanical energy. The data were analysed using the phenomenographic approach. Eight different conceptions and hierarchical relations of the different ways that preservice students understand and use algebraic signs linked with conservation of mechanical energy were identified. The data highlights the need for physics educators to take cognizance of the mix of conceptualizations of algebraic signs compounded with concepts in vector-kinematics and dynamics concepts with regard to conservation of mechanical energy for 1-dimensional motion. The study has implications for the way mechanics is taught at high schools and in tertiary foundation physics.

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