A sonic ranger is used to measure the acceleration of a low-friction cart using data collected from its motion coasting up and down an incline. The uninitiated but experienced physics student may predict the accelerations up and down the incline to be equal. However, when a cart is rolled up an incline, the speed vs time graph produced by sonic ranger clearly shows a point of inflection when the cart reverses direction at its highest point on the ramp. The author then shows how the ratios of the accelerations can be used to determine the coefficient of friction for this event.