科學(英文答)

Question

1)The atmospheric pressure on the Earth is due to the weight of the air molecules in the Earths atmosphere. Suppose a planet P has the same features as the Earth except that it has a (thinner) atmosphere than Earth, i.e. there is less air molecules in this planets atmosphere. Compare the value of the atmospheric pressure on the surface of the planet P to that on the surface of Earth. Explain your answer briefly.

Answer 1

Let us consider water first. a container of 1cm square base area and 10 cm height can contain 10 cm cube water. its mass can be calculated from density X volume = 1X10=10g. It gives 0.001kgX9.8ms-2=9.8N force on the 1cm square base area and gives 9.8 N/cm2 pressure on the base of the container.

atmospheric pressure can be discussed in the same way. On planet P, the atmosphere is thinner, it gives a smaller atmospheric pressure than on earth.

In the same way. If we go up to the top of a mountain, the pressure is smaller there, it is because the air above is thinner. Is it similar to the situation of Planet P?

Since the density of air is not constant, On sea level, the density is larger, high up in the sky, the desity decrease. Detail calculation needs calculus.

2006-10-20 22:20:01 補充：
I am sorry to point out that, the other message(copied below) has error, m should be the mass of air particle. No matter on earth or Planet P, it should be the same. It will not (has a lower m).Since the planet P has fewer air molecules, it has a lower m. Hence, its pressure is lower.

Answer 2

This is actually physics.

We can treat the air molecules as an object circulating the Earth.
P = F/A = ma / A
Since the planet P has fewer air molecules, it has a lower m. Hence, its pressure is lower.