It is generally thought for every mile you walk or run, you burn 100 calories. Supose one were to walk uptown at a 15 degree climb for 2.5 miles and then walk back down 2.5 miles to the original start. It would seem this is harder than just burning 500 calories on a straight 5 mile walk. Newton's first law of motion seems to say, that nothing is achieve walking on level ground, but for the person it is exertion. I don't know what could be said about climbing hills and then coming back down to the original spot. Is there a practical Physics of sorts that has anything to say about this? Or is the only answer an attempt to discover the calories burned on the trip?