Thinking about rotating mass (for example a bike tire) and the disadvantages / advantages that come with differing weights/masses. Most everybody you speak to are programmed to think that a lighter tire will require less energy, thus, everyone tries to find the lightest tire possible. BUT....I'm not so sure about that conclusion, based on different situations. Of course, due to Newton's first two laws, the higher the mass of a rotating object, the more energy will be required to CHANGE its speed. So, from a stop or from a lower rotating speed to a higher rotating speed (or higher to lower too I guess), the more massive the item that must be accelerated, more energy will be necessary to accomplish this. That's fine..... Q 1- However, what about holding a steady speed? Assuming no other outside factors such as friction of all types, if I wanted to HOLD a steady 10mph on level ground, would a heavier tire require LESS, MORE or THE SAME amount of energy ?? (let's assume for this question that the only variable in terms of mass/weight is the TIRE...thus the extra weight is at a distance of 13" from the axis). Q 2- Next.... can anyone speak to the relationship between the distance from the axis/axle and the weight of the mass, in terms energy required to make it rotate (change in speed), and also KEEP it rotating (constant speed)? This obviously has something to do with angular velocity since a weight positioned 1" from the hub would be moving slower (all things equal) than one at 13" from the hub. Thus....this more energy would be required to accelerate the one FURTHER from the hub. But again....what about maintaining a constant speed? Same? More energy....less as the weight moves from closer to the axis to further away from the axis?