I have some questions about atmospheric pressure.?

Question

1) Why is atmospheric pressure at high places, like the top of a mountain, than it is at lower places, like sea level?

2) What causes the pressure of gas? How would increasing the molecules speed affect pressure?

3) Im really confused about this one- what's the difference between pressure and weight. i need explanations. the days of listing 2 separate definitions for each term are over. :(

Answer 1

1) Gravity has an effect of gases, it pulls them toward the center of the earth. The gas at sea level has all the weight of the gas above it. the gas at the top of the mountain only has the weight of the gas above it, not the gases below it.

2)What causes the pressure in a gas is the gas molecules hitting each other. You can have the same number of gas molecules in a container, but when you heat them up, they move faster and the pressure goes up.

3) If you fill an oxygen cylinder to 30 psi, then the contentents of the cylinder is at 30 pounds per square inche pressure. You weigh the cylinder and it is 60 pounds. The cylinder is sent to the space station and is weightless. The cylnder has no weight, but the contents is at 30 psi. It has not changed at the same temperature... Then you send the cylnder to the moon.. On the moon, it weights 10 pounds, but the contents at the same temperature is still 30 psi. You send the contain back to earth and it weighs 60 psi but the contents is still 30 psi. The weight can change depending on the gravity, but the pressure remains the same regardless of the gravity effect on it.

Answer 2

Pressure IS the weight of the column of air above you PER SURFACE UNIT.
At high altitude there is less air above your head, hence the pressure is lower and water boils at less than 100ºC.
Molecule speed (i.e. temperature) may affect pressure. They are proportional because the volume tend to increase with temperature.