Quote Originally Posted by Rjk View Post
as for using fuel, you'll remember from your GCSE physics that energy is proportional to the square of velocity, so even if the journey is taking longer it will use more energy to do it more quickly.
If a car had one gear you might have a point, but it doesn't, so it's nonsense.

For example - suppose I drive for 5 miles at a constant 30mph. One day I drive the whole 5 miles in 4th gear, the next I drive it in 1st. According to your comment, I'd use the same amount of fuel both times.

Cars use gears. The energy used by the engine results in revs per second. 2000 revs per second uses the same amount of fuel regardless of gear.