Which of the following substances is the most abundant in Earth’s atmosphere?
Fill in the blank: The force exerted on an object by the atmosphere in a region of high atmospheric pressure is the force exerted on the object in a region of low atmospheric pressure.
An airplane flies at an altitude of 10 km above sea level. The atmospheric pressure exerted on the plane at this altitude is 0.25 bar.
How many times smaller is this pressure than atmospheric pressure at sea level? Give your answer to the nearest whole number.