Forces on hockey players: Vectors, work, energy and angular momentum

Non-traditional examples can be very inspiring for students. This paper applies classical mechanics to different ways of skating in ice hockey. Skating blades glide easily along the ice in the direction of the blade. Horizontal forces on the skates are thus essentially perpendicular to the blade. Speed skaters glide long distances on each skate before pushing off for the next stride. A hockey player running for the puck may take a number quite short steps in a short explosive rush before shifting to longer strides, where the recurring need to change direction requires additional work by the skater. This paper investigates an alternative stride, with a longer gliding phase in a circular arc, where the centripetal force provided by the ice acting on the skates changes the direction of motion, without the need for additional energy. In addition, the conservation of angular momentum leads to increased speed as the centre of mass is shifted closer to the centre of the circular arc. Finally, we discuss an angular-momentum-based technique to reverse the direction of motion as fast as possible.