Comments by "EebstertheGreat" (@EebstertheGreat) on "The Difference Between Mass and Weight" video.

  1. Yes, well at least they don't deform very much. Trains experience very little rolling friction. Because of their tremendous length (and therefore mas) relative to their cross-sectional area, they also experience very little air resistance relative to their mass. That's why rail transport is so much more efficient.
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  2. Well it is true that if the wheels are rolling without slipping , then no energy is lost to heat. It does take some additional work to make the wheels spin, but the kinetic energy of the spinning wheels is far less than the kinetic energy of the moving car anyway at any speed, so this is generally negligible. But wheels don't roll without slipping. There are still nonconservative forces at work. Most notably, rubber tires deform due to the weight of the car, and this deformation is lossy and heats the tires. At most speeds, this is significantly greater than air resistance and mostly accounts for the reason a car in neutral gear will decelerate on level ground. And importantly, this force does depend on the car's weight, not its mass. So the people in this video were not completely wrong. The reason you sweat more to get the car going is mostly due to its mass, but the reason you have to keep pushing to maintain its speed has more to do with its weight.
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