Force/Work dogs pulling Force is necessary to start all motion, and in the presence of friction force is needed to maintain a constant velocity. In mushing a vast majority of the force comes from the dogs, and depending on the musher as a small amount to no force comes from the musher (assuming flat terrain). Mathematically F = ma where "F" is force, "m" is mass, and "a" is acceleration. this tells us that if the velocity is constant then the sum of the forces equals 0(F = 0). this doesn't mean the dogs aren't applying any force it just means that they are only applying enough force to over come any friction that might be resting the forward motion. The dogs apply this force by pulling on the tug lines which leads to a gangline which is attached to the sled. some mushers place a shock absorber between the sled and the gangline to both ease jolts from the dogs accelerating from a stop and to reduce the jolt on the dogs from large bumps in the trails. . Line set up Work The dogs are only doing work when they are accelerating because W = Fd where W is work, F is force, and d is distance. When the velocity is constant all the forces added up equal 0, so since any number times 0 equals 0, Fd = 0. therefore, no work is done. so even though the dogs have to be applying force constantly the work is equal to 0.