The Effect of Temperature on the Braking Force Experienced by Magnet Falling Through a Copper Pipe

Abstract

The braking experienced by a magnet falling through a conductive pipe is often shown in laboratories, as it is highly intriguing and captures the imagination of students. The Eddy current is the physical phenomenon behind Eddy current braking, which has a lot of utility as Eddy current brakes do not utilise friction and hence do not wear. Linear eddy current brakes, often used on rail vehicles, use the rail as a conductor. Consequently, it is important to address the impact of the rail's properties. Previous papers have explored the significance of thickness and material however temperature has yet to be considered.

Here, coils were wrung around a copper pipe and an oscilloscope was used to determine the position of a neodymium magnet falling through pipe at various temperatures in order to determine the magnet’s terminal velocity. This data was then used to determine the braking force exerted by the pipe on the magnet. The experimental findings were compared to a theoretical model for the braking force. Graphing the inverse of the dragging constant and temperature showed a positive linear relationship suggesting that increasing the temperature reduces the braking force experienced by the magnet, which is in line with pre-existing theory that increasing the temperature will reduce conductivity, in turn reducing the eddy currents that cause the braking force.

Finally, this study establishes that temperature, and hence the weather plays a significant role and needs to be considered when designing eddy current based machines, such as magnetic brakes in high-speed trains.