Air is a fluid, too. It's also got a lower viscosity than say, water, so it will create less resistance. Saying it stores a lot more energy when it moves is li

Air is a fluid, too. It's also got a lower viscosity than say, water, so it will create less resistance. Saying it stores a lot more energy when it moves is like saying that we should make our train cars heavier so that we can recover more energy by regenerative braking.