Why is it that when a steadily flowing gas flows from a larger diameter pipe to a smaller diameter pipe, what causes the pressure in the smaller pipe to drop?

If a star is moving toward earth, it is

The amount of heat required to change liquid water to vapor at its boiling temperature is 2256 kj/kg. the amount of heat required to change liquid mercury to its vapor state at its boiling temperature is 295 kj/kg. one kg of each substance is currently at its boiling point. how will the amount of thermal energy required to change each substance from a liquid to a gas differ?

Which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?