My name is Derek Cox, I am new to the forum and I am not an engineer or anything close. I have a degree in flight management and I am a commercial plumber that works on large scale construction projects. Here are my questions but first I will give you some background on the questions. I am not looking for exact calculations unless they are easy. I am really looking for an easy method of calculating this out. I own a few dogs that compete in weight pull competitions. The dogs are trained to pull. Generally the dogs pull on a track with rails of angle iron and the cart has v-groove casters, the dog works on carpet. The other option is a cart with pneumatic tires; the cart and the dog are on carpet. The dogs pull 16 feet and then the pull is complete. It is amazing at the amount of weight some of these dogs can pull. http://www.youtube.com/watch?v=7CDuL3JzpZA&feature=related" So my first question: Does friction increase exponentially as weight increases. For example, 2 dogs with the same strength per pound one weighs 50 pounds and one weighs 100 pounds. The small dog can pull 500 pounds (10 times its own weight) versus the big dog can only pull 800 pounds (8 times its own body weight). If this is true is there a formula to use for this application? Second question: If the track is set on an incline of 2 inches over a 16 foot span what does the load force or friction factor increase the force to pull it? Example: A dog pulls 2000 pounds on a track as mentioned above (2” over 16’) does that take the same force to pull as 3000 pounds on a level surface? Also is there a formula for this question? I know there are some different factors that may need to be known. Just let me know I will do the best I can. Thanks for all the help.